RU2594364C2 - System of measuring concentration of boric acid in first circuit of heat carrier of nuclear power reactor - Google Patents

Abstract

FIELD: energy.

SUBSTANCE: invention relates to nuclear power engineering and relates to a system for measuring concentration of boric acid in a first circuit of heat carrier of a nuclear reactor. System comprises two laser radiation sources, measuring and reference cell, photodetector unit, signal processing unit, control unit, laser radiation parameter measuring unit, two laser radiation modulators, three optical switches, three controlled optical attenuators, controlled spectral filter, four fibre-optic lines, five reflecting and five semitransparent mirrors.

EFFECT: technical result consists in improvement of efficiency, safety and accuracy of measurements.

17 cl, 11 dwg, 1 tbl

Description

The invention relates to the field of measuring equipment and nuclear energy and is intended for use in a nuclear power reactor of a nuclear power plant for continuous monitoring and operational measurement of the concentration of boric acid in the coolant of a VVER-type nuclear reactor. Boric acid, contained in the form of an aqueous solution in the coolant, contains a chemical element Bor-10, the atomic nucleus of which is an effective absorber of neutrons generated during the operation of a nuclear reactor. The number of Boron-10 atoms in the composition of the coolant is a factor determining the operating mode of a nuclear reactor. By changing the number of boron atoms in the coolant, you can change the operating mode of a nuclear reactor. The composition of one molecule of boric acid (H ₃ BO ₃ ) includes one atom of Boron-10. The concentration of Boron-10 atoms is proportional to the concentration of boric acid in its aqueous solution in the composition of the coolant of a nuclear reactor. Therefore, the measurement of the concentration of boric acid in the coolant circuit is identical to the determination of the concentration of Boron-10 atoms in the specified coolant, which is an important factor in controlling the operation and ensuring the safety of the nuclear power reactor.

There are various methods for determining the concentration of boron atoms and boric acid in the composition of the coolant circuit of a nuclear reactor. One of the most well-known and practically used methods is the method of direct sampling from the coolant circuit of a nuclear reactor and subsequent chemical measurement of the concentration of boric acid in the composition of the obtained sample — the so-called chemoluminescent method for determining the concentration of boric acid [1, 13]. According to this method, the material of the sample taken from the coolant circuit is treated with lucigenin, alkali and hydrogen peroxide. The concentration of boric acid is determined by the level of luminescence of the processed sample, which is proportional to the concentration of boric acid. The disadvantages of this measurement method include the low accuracy of measurements, due to the large number of factors that arise when processing a sample with a set of special substances and affect the level of luminescence, in addition to the actual concentration of boric acid. The implementation of this method is associated with a number of great technical difficulties caused by the radioactivity present in the coolant circuit and the surrounding premises of the nuclear reactor, which leads to the need for special and expensive means to prevent irradiation of the reactor technical personnel, which ensures sampling from the coolant circuit. The equipment for sampling directly from the coolant circuit is very complex and cumbersome due to the high temperature and pressure of the working substance - distilled water - in the coolant circuit and introduces additional errors in the measurement process. In addition, the process of sampling and subsequent chemical determination of the concentration of boric acid takes a lot of time, and does not allow you to quickly and efficiently obtain information on the concentration of boron atoms in the coolant, which is necessary for effective control of the operation of a nuclear reactor. Known radiation methods for determining the concentration of Boron-10 in the coolant of a nuclear reactor [2], based on the registration of the neutron flux at the outlet of the nuclear reactor. Such methods include a method for controlling the content of Boron-10 in the primary circuit of the coolant of a nuclear reactor according to RF patent No. 2025800 [3]. The method is based on measuring the neutron flux through a coolant at the outlet of a nuclear reactor. In this case, neutrons with energies up to 0.6 eV and neutrons with energies above 0.6 eV are recorded separately, and with respect to these neutron fluxes, an increase in the concentration of Boron-10 in the composition of the coolant of a nuclear reactor is judged. The disadvantages of this method include the low accuracy of measurements, which allows the measurement of boron concentration of the order of units of grams per liter of coolant. In addition, for the implementation of this method, it is necessary to locate the measuring equipment directly in the working zone of the nuclear reactor, which is very difficult to control the functioning and maintenance of the equipment.

The most effective and accurate method for measuring the concentration of boron and boric acid in its aqueous solution, i.e. in the coolant of a nuclear reactor, is an optical photometric measurement method. The application of this method is based on direct photometry and measurement of the luminous flux of the corresponding wavelength transmitted through the coolant substance in the circuit of a nuclear reactor directly in its operating mode, without any sampling and without the use of any additional effects on the coolant substance with chemicals, as in chemoluminescent measurement method, as well as without measurements of radiation radiation fluxes. To implement this measurement method, a measuring flow cell with optically transparent porthole windows using a bypass, a special branch pipe, must be inserted into the primary circuit of the nuclear reactor coolant. Photometric methods for measuring the concentration of substances in a gas or water medium are known and are successfully used in various technical fields. However, the application of this method in nuclear energy presents certain technical requirements for the equipment and requires the solution of a number of complex problems and tasks. It should be noted the impossibility of placing the equipment near the working zone of the reactor and the need to remove the measuring equipment from the radiation exposure zone and its location at a considerable distance from the measuring cell, the requirement for high accuracy in measuring very low concentrations of boric acid (about 0.5 mg / l of coolant) in the end of the working session of the nuclear reactor, ensuring high reliability and confidence of the measurement results, as well as the requirement of high operational sti in carrying out measurements. The presented invention is aimed at solving these problems.

Known devices that implement the photometric method for measuring the concentration of substances contain a radiation source, a photodetector, a measuring cell, with which the measuring and reference measurement channels are formed, a measurement processing circuit. The disadvantage of these devices is the relatively low measurement accuracy, especially manifested at a low concentration of the measured substances due to the low absorption capacity of the measured substance. To overcome this drawback, an increase in the length of the measuring cell is usually carried out, or a multi-pass cell is used. However, these methods of increasing accuracy are not applicable for measurements in a nuclear reactor. Known two-beam photometer with a multi-way cell [4] according to the patent of England No. 1157086. The device contains a radiation source, measuring and comparative channels (cuvettes), a mirror modulator, a photodetector, a signal conversion unit. The disadvantages of the device include the low accuracy of measurements.

A device [5] according to the patent of the Russian Federation No. 2022239, designed for optical absorption analysis of a gas mixture. The device contains an infrared radiation source, a broadband filter, a measuring cell, an interference filter, a photodetector filled with nitrous oxide. The disadvantages of this device include the low accuracy of the measurement, which is due to the instability of the parameters of the source of infrared radiation and the radiation receiver and the inability to compensate for this instability. As a prototype, the device closest in technical essence to the patent of the Russian Federation No. 750287 [6] was selected. The device is a two-beam photometer and is intended for optical absorption analysis and determination of concentrations of substances in the liquid phase. This device contains a radiation source with a condenser, a multi-way (two-way) cell with the test substance, a measuring and comparative channels, an interference filter, two photodetectors, a mirror mechanical modulator, a differential cascade, a signal processing and control unit. The disadvantages of this device include the low measurement accuracy, especially manifested when measuring low concentrations of substances. This is due to the impossibility of increasing the length of the measuring cell when measuring low concentrations of the substance, as well as the influence of the spread in sensitivity of the two photodetectors used and the lack of compensation for this spread. It should also be noted that it is fundamentally impossible to use a measuring optical device created according to this scheme for carrying out measurements in an operating nuclear reactor. This is due to a number of specific requirements for equipment for measuring the parameters of the coolant in the primary circuit of a nuclear reactor. Such requirements and current factors include the impossibility of measuring equipment being located near a nuclear reactor and the need to remove the equipment to a separate room protected from radiation at a considerable distance from the reactor - about 25 meters, as well as the impossibility of increasing the length of the measuring cell over one meter and the inability to use a multi-way cell having increased dimensions (in diameter) and requiring periodic maintenance by technical personnel.

The aim of the invention is to overcome these drawbacks and create a measuring system for optical absorption analysis and continuous remote measurement of boric acid concentration in the primary circuit of the coolant of a WWER-type nuclear reactor with high accuracy, which ensures the measurement of low concentrations of boric acid. Measurement of the parameters of the primary coolant of a nuclear reactor is carried out remotely in an automatic mode and with high efficiency, without the participation of maintenance personnel who are not exposed to any radiation hazard. The proposed measuring system provides the ability to measure with high accuracy large concentrations of boric acid in the composition of the coolant of the order of tens of grams per liter of coolant at the beginning of the working session of a nuclear reactor, as well as the measurement of small concentrations of boric acid in the composition of the coolant of the order of 0.5-0.1 mg / l at the end of a working session of a nuclear reactor. This is realized through the use of special tools that ensure multiple passage of the measuring laser radiation through the measuring cell with limited dimensions, allowing for use in a nuclear reactor.

Achievable technical result is an increase in the accuracy of measuring the concentration of boric acid in the primary circuit of the coolant of a nuclear reactor, the implementation of measurements of small concentrations of boric acid in the composition of the coolant, ensuring high efficiency of measurements remotely at a considerable distance from the existing nuclear reactor without the participation of maintenance personnel.

The specified technical result is achieved as follows and is demonstrated in the form of two options for constructing a system for measuring the concentration of boric acid in the coolant circuit of a nuclear reactor.

The first option to build a measurement system

1. In the system for measuring the concentration of boric acid in the first coolant circuit of a nuclear power reactor, comprising a first laser generator, a measuring and reference cell, electrically coupled photodetector unit, a signal processing unit and a control unit, the photodetector unit equipped with a lens, and the control input of the first laser the generator is connected to the control unit, the second laser generator, the first and second laser radiation modulators, the first, second and third optical switches, four are introduced fiber optic lines, three controlled optical attenuators, a controlled spectral filter, a unit for measuring laser radiation parameters, five reflective mirrors and five translucent mirrors, while the optical outputs of the first and second laser generators are connected to the optical inputs of the first and second laser radiation modulators, respectively , the optical output of the first laser modulator is connected to the optical input of the first optical switch by sequentially mounted on the optical axis of the first, second and third translucent mirrors, the optical output of the first laser modulator is additionally connected to the optical input of the third controlled attenuator through the first and second translucent mirrors, the optical output of the second laser modulator is connected to the optical input of the first optical switch by the fourth reflective mirror, the first , the second and third translucent mirrors, the optical output of the second laser modulator is additionally op connected with the optical input of the third controlled attenuator by means of the fourth reflective mirror, the first and second translucent mirrors, the first optical output of the first optical switch is optically connected to the input of the first fiber optic line through the first optical attenuator, the optical output of the first fiber optic line is connected to the optical input measuring cell, the second optical output of the first optical switch is optically connected to the input of the third fiber optic line through h second controlled attenuator, the optical output of the third fiber optic line is connected to the optical input of the reference cell, the optical output of the measuring cell is connected to the input of the second fiber-optic line, the optical output of which is connected to the first optical input of the third optical switch, the optical output of the reference cell optical input of the fourth fiber optic line, the output of which is connected to the second optical input of the third optical switch, the optical output of the third optical the switch is optically connected to the optical input of the first optical switch by means of sequentially mounted and optically coupled third reflective mirrors, a fifth translucent mirror, a second reflective mirror and a third translucent mirror, the optical output of the third optical switch is additionally connected to the first optical input of the second optical switch by a third reflective mirror and fifth translucent mirror, the optical output of the third control of the second attenuator is connected to the second optical input of the second optical switch by means of the fourth translucent mirror, the first and fifth reflective mirrors, the optical output of the third controlled attenuator is additionally connected to the optical input of the laser radiation measurement unit by the fourth translucent mirror, the optical output of the second optical switch is connected to the optical input controlled spectral filter, the optical output of which is connected to the optical input of the object willow of the photodetector unit, the control input of the second laser generator and the control inputs of the first and second laser radiation modulators are connected to the control unit, the control inputs of three optical switches and three controlled attenuators are connected to the control unit, the control input of the controlled spectral filter is connected to the control unit.

2. In the measurement system according to paragraph 1, the ultraviolet wavelength laser generator is used as the first laser generator.

3. In the measurement system according to paragraph 1, the first and second laser generators are configured to tune the wavelength of the generated laser radiation.

4. In the measurement system according to paragraph 1, the optical switches contain a reflective mirror and a stepper motor.

5. In the measurement system of claim 1, the controllable spectral filter is based on an acousto-optical cell operating in the ultraviolet wavelength range and in the short-wavelength part of the visible wavelength range.

6. In the measurement system according to claim 1, the controllable spectral filter contains two acousto-optic cells and two optical switches, including acousto-optic cells alternately in the optical circuit of the measurement system.

7. In the measurement system according to paragraph 1, the reference cuvette is equipped with a working substance filling unit, equipped with inlet and outlet taps.

The second option to build a measurement system

A technical new result is achieved as follows:

8. In the system for measuring the concentration of boric acid in the primary circuit of the coolant of a nuclear power reactor, comprising a first laser generator, a measuring and reference cell, electrically coupled photodetector unit, a signal processing unit and a control unit, the photodetector unit provided with a lens, and the control input of the first laser the generator is connected to the control unit, the second laser generator, the first and second laser frequency shift blocks, the first, second and third optical switches are introduced and, four fiber-optic lines, three controlled optical attenuators, a controlled spectral filter, a unit for measuring laser radiation parameters, five reflective mirrors and seven translucent mirrors, the optical output of the first laser generator being connected to the optical input of the first optical switch by sequentially mounted on the optical the axis of the first, second and third translucent mirrors, the optical output of the first laser generator is additionally connected to the optical input of the third o controlled attenuator by means of the first and second translucent mirrors, the optical output of the second laser generator is connected to the optical input of the first optical switch by the fourth reflective mirror, the first, second and third translucent mirrors, the optical output of the second laser generator is additionally optically connected to the optical input of the third controlled attenuator by the fourth reflective mirror, the first and second translucent mirrors, the first optical output of the first of the optical switch is optically connected to the input of the first fiber optic line through the first optical attenuator, the optical output of the first fiber optic line is connected to the optical input of the measuring cell, the second optical output of the first optical switch is optically connected to the input of the third fiber optic line through the second controlled attenuator , the optical output of the third fiber optic line is connected to the optical input of the reference cell, the optical output of the measuring cell is connected to the input the second optical fiber line, the optical output of which is connected to the first optical input of the third optical switch, the optical output of the reference cell is connected to the optical input of the fourth optical fiber line, the output of which is connected to the second optical input of the third optical switch, the optical output of the third optical switch is optically connected with the optical input of the second laser frequency shift unit through a third reflective mirror, a fifth translucent mirror and W of the third reflective mirror, the optical output of the second laser frequency shift unit is optically connected to the optical input of the first optical switch via a third translucent mirror, the optical output of the third optical switch is additionally connected to the first optical input of the second optical switch by the third reflective mirror and the fifth translucent mirror, optical output the third controlled attenuator is connected to the second optical input of the second optical the switch through the fourth translucent mirror, the first reflective mirror and the sixth translucent mirror, the optical output of the third controlled attenuator is additionally connected to the optical input of the laser radiation measuring unit by the fourth translucent mirror, the optical output of the third controlled attenuator is optically connected to the optical input of the first laser frequency shift unit through the fourth translucent mirror, the first reflective mirror and a sixth translucent mirror, the optical output of the first laser frequency shift unit is optically coupled to the optical input of the objective of the photodetector unit via the sixth reflective mirror and the seventh translucent mirror, the optical output of the second optical switch is connected to the optical input of a controlled spectral filter, the optical output of which is connected to the optical input the lens of the photodetector block through the seventh translucent mirror, the control inputs of the second laser generator, ne The first and second blocks of the frequency shift of the laser radiation are connected to the control unit, the control inputs of three optical switches and three controlled attenuators are connected to the control unit, the control input of the controlled spectral filter is connected to the control unit.

9. In the measurement system of claim 8, a laser generator of the ultraviolet wavelength range is used as the first laser generator.

10. In the measurement system of paragraph 8, the first and second laser generators are configured to tune the wavelength of the generated laser radiation.

11. In the measurement system of claim 8, the optical switches comprise a reflective mirror and a stepper motor.

12. In the measurement system of claim 8, the controllable spectral filter is based on an acousto-optic cell operating in the ultraviolet wavelength range and in the short-wavelength part of the visible wavelength range.

13. In the measurement system of claim 8, the controllable spectral filter contains two acousto-optic cells and two optical switches, including acousto-optic cells alternately in the optical circuit of the measurement system.

14. In the measurement system of claim 8, the first laser frequency shift unit comprises optically coupled input diaphragm, acousto-optic cell with control unit, first lens, pinhole, second lens and output diaphragm sequentially mounted on the optical axis, while the control electrode of the acousto-optic cell is connected to the control unit acousto-optic cell.

15. In the measurement system of claim 8, the second laser frequency shift unit comprises two acousto-optic cells and two optical switches, including acousto-optic cells alternately in the optical circuit of the measurement system.

16. In the measurement system according to paragraph 8, the reference cell is equipped with a working substance filling unit, equipped with inlet and outlet taps.

17. The measurement system according to paragraph 8 contains three measuring cuvettes, optically coupled through fiber optic lines with optical inputs of six additional optical switches, alternately including the measuring cuvettes in the optical circuit of the measuring system, the measuring cuvettes connected to the first coolant circuit of a nuclear power reactor in it various points.

In FIG. 1 shows a block diagram of the first embodiment of the proposed system for measuring the concentration of boric acid in the coolant circuit of a nuclear reactor. The numbers in FIG. 1, the following elements are indicated:

1 - the first laser generator;

2 - a measuring cell equipped with windows transparent to laser radiation;

3 - reference cell;

4 - photodetector block;

5 - signal processing unit;

6 - control unit;

7 - lens photodetector unit;

The following are the newly introduced elements:

8 - second laser generator;

9 - the first translucent mirror;

10 - second translucent mirror;

11 - the third translucent mirror;

12 - the first optical switch;

13 - reflective mirror of the first optical switch;

14 - the first controlled attenuator with a control unit pos. fifteen;

15 - control unit of the first attenuator;

16 - second controlled attenuator with a control unit pos. 17;

17 - control unit of the second attenuator;

18 - the third controlled attenuator with the control unit pos. 19;

19 - control unit of the third attenuator;

20 is a block measuring the parameters of laser radiation;

21 is a second modulator of laser radiation;

22 - the first modulator of laser radiation;

23 - the second optical switch;

24 - reflective mirror of the second optical switch;

25 - the third optical switch;

26 - reflective mirror of the third optical switch;

27 - controlled spectral filter;

28 - the first fiber optic line;

29, 30 - fiber adapters of the first fiber optic line, performing the function of matching optical beams and which are the optical inputs and outputs of the fiber optic line;

31 - second fiber optic line;

32, 33 - fiber adapters;

34 - third fiber optic line;

35, 36 - fiber adapters;

37 - the fourth fiber optic line;

38, 39 — fiber adapters;

40 - fourth translucent mirror;

41, 42, 43 and 44 - the first, second, third and fourth reflective mirrors, respectively;

45 - the fifth translucent mirror;

46 and 47 — inlet and outlet nozzles of the measuring cell for connecting it to the first coolant circuit of a nuclear reactor;

49 - block filling the reference cell with a working substance;

50 - fifth reflective mirror.

The first and second laser generators (items 1 and 8) include laser radiation shapers.

In FIG. 2 is a block diagram of a second embodiment of a system for measuring the concentration of boric acid in the first coolant circuit of a nuclear reactor. In FIG. 2 elements similar to the first embodiment of the measurement system in FIG. 1 are indicated by the same numbers. In a second embodiment of the system of FIG. 2, there are the following differences from the first embodiment of the system of FIG. one.

There are no (excluded) modulators of laser radiation position 21 and 22.

Fifth Reflective Mirror Pos. 50 is excluded and replaced by the sixth translucent mirror pos. 51, mounted in the same place as the reflective mirror 50 in the optical circuit.

The following elements have been added (re-entered):

52 - the first block of the frequency shift of the laser radiation;

53 - the second block of the frequency shift of the laser radiation;

54 - sixth reflective mirror;

55 - the seventh translucent mirror.

In FIG. 1 and FIG. 2, the intersection of fiber optic lines 34 and 38 with open optical lines occurs in different planes and does not affect the operation of the measuring system.

In FIG. 3 is a block diagram of a controllable spectral filter (27 in FIG. 1) containing the following elements, indicated by numbers:

56 and 57 — acousto-optical cells;

58 and 59 — control units containing electric signal generators;

60 and 61 are optical switches;

62-65 - reflective mirrors;

66 and 67 - piezoelectric elements;

68 and 69 - input and output diaphragms.

In FIG. 4 is a block diagram of a first laser frequency shift unit (key 52 in FIG. 2), where the following elements are indicated:

70 and 71 — acousto-optical cells;

72 and 73 - control units containing electrical generators;

74 and 75 are optical switches;

76-79 - reflective mirrors.

80 and 81 - input and output diaphragms.

In FIG. 5 is a block diagram of a second laser frequency shift unit (key 53 in FIG. 2), where the following elements are indicated:

82 — acousto-optic cell; 82.1 — piezoelectric element;

83 is a control unit containing an electric signal generator;

84 is a lens;

85 - point aperture.

86 is a lens;

87, 88 - input and output diaphragms.

In FIG. Figure 6 shows an embodiment of a measurement system based on the use of open lines of optical communication between the measuring cell 2 and the measuring circuit instead of fiber optic lines. Elements matching the elements in FIG. 1 and FIG. 2 are indicated by the previous numbers. The new numbers indicate the following newly entered elements:

89-94 - reflective mirrors;

95 and 96 - protective covers.

In FIG. 7 is a diagram of a first optical switch (key 12 in FIG. 1 and FIG. 2), which is in a state of connecting a reference cell to a measurement circuit. The designations correspond to similar elements in FIG. 1 and FIG. 2.

In FIG. 8 is a block diagram of an embodiment of a measurement system comprising several measurement cells. In this embodiment, the measurement system contains three measuring cuvettes. Previous elements are indicated by the corresponding previous numbers. New items are indicated by the following numbers:

97 and 98 - additional measuring ditches;

99-104 - additional optical switches;

105-108 - additional fiber lines.

In FIG. 9, FIG. 10 and FIG. 11 presents the results of modeling the measurement process during measurements in this measurement system of the parameters of the coolant with a concentration of boric acid of 0.5 mg / l (Fig. 9), 0.25 mg / l (Fig. 10) and 0.1 mg / l (Fig. 11).

The measuring system (Fig. 1 and Fig. 2) works as follows. The system continuously measures the optical parameters of the coolant substance directly in the primary coolant circuit of a nuclear reactor. The measurement of optical parameters is carried out by the absorption spectral method, by transmitting laser radiation generated by the first laser generator pos. 1 (see Fig. 1) through a measuring cuvette 2 and subsequent measurement of the optical parameters of the laser radiation transmitted through the cuvette 2 using a photodetector 4. Measuring cuvette 2 is connected to the first coolant circuit of a nuclear reactor by means of a special bypass ( bypass pipeline). This ensures that the volume of the measuring cell 2 is filled with the substance of the coolant circulating in the primary coolant of the nuclear reactor. Measuring cell 2 is equipped with special optical windows transparent for laser radiation of laser generators pos. 1 and 8. The measuring cell 2 is located near the nuclear reactor in the radiation zone, and is connected to the rest of the measuring equipment located in the non-radiation zone by fiber optic lines 28 and 31. Thus, using the measuring cell 2, located separately from the measuring equipment, the optical parameters of the coolant are measured directly in the primary circuit of the coolant of a nuclear reactor. In the measurement system, the first laser generator pos. 1 is the main source of probing laser radiation, at a wavelength of which the optical transmission characteristics of the probing laser radiation are measured by the studied substance of the coolant - boric acid solution. The second laser generator 8 is an auxiliary generator and generates laser radiation in the longer wavelength region of the spectrum. Using this laser radiation, the measurement system is monitored and tested, and the optical transmission parameters of the measuring and reference cuvettes are parallel tuned. The reference cell 3 is equipped with fiber optic lines (keys 34 and 37), similar to the fiber optic lines 28 and 31, connecting the measuring cell 2 to the optical circuit of the measurement system. This allows you to fine-tune and calibrate the measurement system using the well-known parameters of the reference solution of boric acid contained in the reference cell 3.

The absorption spectral method is based on the determination of the optical characteristics of the transmission and absorption of substances in certain spectral ranges and wavelengths. The use of the absorption spectral method for measuring the optical characteristics of substances is based on the physical laws of Beer and Bouguer-Lambert. The Bouguer-Lambert law determines that when light passes through a layer of matter, the fraction of absorbed energy is determined by the thickness L (length) of the path traveled by the light in the test substance. In accordance with this, the magnitude of the energy of the light flux I passing through the layer of the test substance with a thickness L can be determined by the formula:

where I ₀ is the initial (input) incident light flux (at the entrance to the measuring cell 2); α is the absorption coefficient of light radiation when passing through the layer of the investigated substance located in the measuring cell 2. The optical density of the substance (absorbability) D is equal to:

According to Beer's law, the optical density D is proportional to the concentration C of the test substance

where K is the coefficient of proportionality, called the extinction coefficient and characterizing extinction (extinction). Thus, the basic equation relating the incident and transmitted light fluxes and the concentration of the test substance C can be represented in the following form:

where the following quantities and dimensions were used: L [cm] - layer thickness of the test substance (length of the measuring cell), C [g / l] - concentration of the test substance, K [l · g ^-1 cm ^-1 ] - extinction coefficient.

The extinction coefficient is a value that determines the luminous flux attenuating ability of a certain unit concentration of the test substance on a unit path of light radiation (L = 1 cm). The extinction coefficient depends on the wavelength λ of the light radiation passing through the layer of the test substance K = K (λ).

Thus, when using the absorption spectral method to determine the concentration of a substance, for example, the concentration of boric acid in its aqueous solution, it is first necessary to determine (or have previously obtained from previous studies) the extinction coefficient of the boric acid solution K at the wavelength of optical radiation, used to illuminate the studied layer of matter. Next, the values (energy) of the incident and transmitted optical radiation are measured. After measurements of the luminous flux values, the desired concentration of the test substance is determined - the concentration of boric acid in the measuring cell 2, through which the light flux from the first laser generator 1 passed, according to the following formula obtained from the main relation (4):

where V is the value by which the light flux decreases when passing through the layer of the investigated substance with a thickness (length) L.

Equation (5) is the main one for determining the concentration of a substance in the absorption spectral method and is well known in the technical literature. In the proposed measuring system, this equation is used to measure relatively large and medium concentrations of boric acid in the composition of the coolant of a nuclear reactor - ranging from tens of grams per liter at the beginning of a session of a nuclear reactor, to tenths of a gram per liter of volume of coolant in the middle of the session . To measure lower concentrations, a special measurement mode is used, which is discussed below. It should be noted that boric acid, which is present in the composition of the coolant in the form of an aqueous solution, is characterized by a very small absorption of optical radiation and, accordingly, a small value of the extinction coefficient. A noticeable absorption of optical radiation by boric acid takes place in the ultraviolet wavelength range of 200-400 nanometers, however, even in this range the absorption of radiation by boric acid is very small and requires special measures to increase the sensitivity of the absorption spectral method when measuring small values of boric acid concentration, necessary when monitoring and controlling the operation of a nuclear power reactor.

It should be noted that the quantity (product) KL in relation (5) determines the sensitivity of the absorption spectral measurement method. Indeed, the main technically measurable quantity is the value V in (5), which is determined and caused by a decrease in the level of luminous flux after passing through the measuring cell, compared with the level of light flux at the entrance to the measuring cell. The measurement of the parameters of the light flux (radiation) after passing through the layer of the investigated substance is the main operation of the absorption spectral method. The main measurable parameter here is the ratio P _meas = V / I ₀ , which is further used in relation (5) to directly determine the concentration of boric acid or other substances measured by this method. To ensure a sufficiently high accuracy of measurements of the levels of light fluxes using modern equipment, the ratio P _ism must exceed a certain threshold level for measuring small values in the specified equipment. For modern measuring equipment, this level is of the order of 1%, hence the value of the recorded relative decrease in luminous flux P _ISM = V / I ₀ should be not less than 0.01: P _ISM > 0.01. Thus, when performing measurements by the absorption-spectral method in order to obtain the high required measurement accuracy, the relative value Р _{ism of the} decrease in the luminous flux should be not less than one percent of the luminous flux arriving at the input of the measuring cell and satisfy the relation

It can be argued that the value of the ratio P _ISM = 0.01 determines the threshold value of the minimum concentration of boric acid, which can be measured at a given known extinction value K at the optical radiation wavelength selected for measurements. According to relations (4) and (5), the minimum measured concentration C _min is equal to the following value, determined from the relation

Expanding in series the exponential for small values of K and C, we obtain for C _min :

The value C _min in (5.3) determines the lowest-possible to measure the concentration of boric acid and a sensitivity of (potential) absorption and spectral sensitivity of the method and also apparatus used for the measurement. From (5.3) it follows that the sensitivity of the method is determined by the product of the KL values and increases (in the sense of decreasing the minimum recorded value C _min ) with increasing product KL. Boric acid is characterized by a very small value of the extinction K, which significantly increases, according to (5.3), the minimum recorded concentration of boric acid and, accordingly, leads to a deterioration in the sensitivity of the measuring equipment used. Therefore, when making measurements of low concentrations of boric acid, the problem of increasing the sensitivity of measuring equipment arises, the solution of which is proposed in the present invention. The standard absorption spectral method allows measurements of relatively high concentrations of boric acid.

The measurement of large and medium values of the concentration of boric acid in the composition of the coolant of a nuclear reactor circulating through a measuring cell 2 is carried out as follows (in the first version of the construction of the measurement system).

The laser generator 1 is the main one and generates laser radiation (LI) in the ultraviolet region of the spectrum, in which boric acid has the highest absorption capacity, i.e. extinction coefficient K is of greatest importance. Second laser generator pos. 8 performs additional monitoring functions and adjusts the operating mode of the measurement system. The laser generator 8 generates laser radiation in the blue or green region of the visible spectrum, in which there is practically no absorption of optical radiation by boric acid, which allows using this LI from the laser generator 8 to jointly configure and test a measuring 2 and reference 3 cell. Laser generators 1 and 8 operate separately. The laser radiation modulator 22 generates laser radiation pulses with a short duration, for example, of the order of 100 ns. The pulse repetition rate is of the order of one pulse per second. A higher repetition rate is not required, since the concentration of boric acid in the coolant flowing through the measuring cell 2 is determined from one generated laser pulse. Concentration C is the main measured parameter of the measuring system. The generated laser pulse from the output of the laser radiation modulator 22 is fed to the input of the fiber adapter 30 of the first fiber-optic line 28 through the following elements located along the propagation of this laser pulse: through translucent mirrors pos. 9, 10 and 11, as well as after reflection from the reflective mirror 13 of the first optical switch 12 and through the first controlled attenuator 14. The first, second and third optical switches are turned on, as shown in FIG. 1, for transmitting LI into the measuring cell 2, receiving radiation transmitted through the measuring cell 2 and for transmitting the transmitted laser radiation to the input of the photodetector unit 4. After passing through the first fiber-optic line 28, the laser radiation through the fiber adapter 29 enters the measuring input the cuvette 2, passes through it, and then through the fiber adapter 32, the second fiber optic line 31 and the fiber adapter 33 then goes to a number of optical elements directing the pulses passed through the measuring cuvette 2 from laser radiation to the input of the photodetector unit 4. To direct this LI pulse to the input of the photodetector unit 4, the following optical elements are used through which the laser pulse passes: a reflection mirror 26 of the third optical switch 25, a reflection mirror 43, then through a translucent mirror 45 in direct course, the reflective mirror 24 of the second optical switch 23, through a controlled optical filter 27. From the output of the last laser pulse is supplied to the input of the lens 7 and then to the photodetector ny unit 4. In the latter being registered laser pulse, converting it into an electrical pulse which is supplied later in the signal processing unit 5. The pulse amplification is performed In the latter, digitizing the pulse, the measurement of the pulse amplitude in a digital form. After that, information about the parameters of the pulse in digital form enters the control unit 6, where information is stored in a special memory register. In parallel with the registration of the parameters of the laser pulse transmitted through the measuring cell 2, the measurement and registration of the parameters of the laser pulse received at the optical input of the measuring cell 2 from the output of the fiber adapter 29. For this, the pulse parameters are measured using the unit for measuring the parameters of the laser radiation 20 LI received at the input of block 20 from the output of the laser radiation modulator 22 through translucent mirrors 9 and 10, the third controlled attenuator 18 and semi-transparent a transparent mirror 40. Block 20 comprises a photodetector for detecting an incoming LI pulse, as well as a circuit for amplifying and digitizing an electric signal pulse. Further, the received information from the output of the measuring unit 20 enters the control unit 6, where the pulse parameters are stored and processed together with the pulse received at the input of the photodetector 4. When processing the pulse from the output of the measuring unit LI 20, the previously known and located in the memory of the processing unit 6 of information on the parameters of transmission of laser radiation by the elements through which the laser passes before entering the unit 20, namely: transmission of translucent mirrors 9, 10 and 40, transmission of control trolled attenuator 18, which is a point in time set by commands from the control unit 6. Simultaneously, in the processing unit 6 is carried out keeping the attenuation of the laser radiation as it propagates from the output of the modulator 22 to the optical LEE enter the measuring cuvette 2 (yield fiber adapter 29). In this case, the transmission of the elements of the translucent mirrors 9, 10, 11 is taken into account, as well as the slight attenuation in the fiber line 28 and in the first controlled attenuator 14, which is set by commands from the control unit 6. Taking into account these factors, information is generated in the control unit 6 the amplitude (energy) of the laser pulse I ₀ received at the optical input of the measuring cell 2. Similarly, in the control unit 6, the magnitude of the amplitude (energy) of the laser pulse transmitted through measuring cuvette 2 and registered by the photodetector unit 4. In this case, the transmission of the fiber line 31, the translucent mirror 45 and the transmission of the controlled filter 27 are taken into account, the transmission value of which at the wavelength of the laser generator 1 is set by commands from the control unit 6. Then, in the control unit 6, obtained (measured) data values of the levels of the laser pulses to I I ₀ and after passing through the measuring cell 2 according to the formula (5) computes the concentration value bo acid C in the composition of the coolant passing through the cuvette 2 with the length of the working zone L. In this case, the extinction coefficient K is used at the radiation wavelength of the laser generator, obtained from the passport data for boric acid, or K value obtained by special measurements, for example using the proposed measuring system. The information received is transmitted further to the nuclear reactor control panel.

To increase the accuracy of measurements in the measuring system, a special mode of testing and joint calibration of the sensitivity of the photodetectors included in the unit for measuring the parameters of laser radiation 20 and the photodetector unit 4 is provided. To implement the specified calibration mode, the second optical switch 23 rotates the reflective mirror upon a command from the control unit 6 24 by 180 degrees (relative to the axis of block 23), as a result of which the reflective mirror occupies a position at which the laser pulse polar radiation propagating from the modulator 22 via DID key elements. 9, 10, 18, 40 and 41, after reflection from the reflective mirror 50 and the reflective mirror 24 in its new position, it is fed to the optical input of the controlled spectral filter 27 and then to the input of the photodetector unit 4. When the received laser pulse is recorded by the photodetector unit 4, it is used information about the transmission of these optical elements. As a result, joint mutual calibration is carried out, the readings are refined, and the photodetector unit 4 and the laser radiation parameters measurement unit 20 are brought to a single measurement scale, which eliminates the influence of the variation in the sensitivity parameters of these elements. When performing calibration operations of photodetectors, the measurement of laser radiation transmitted through the measuring cuvette 2 is not performed.

Measurement of boric acid concentration on the basis of a single passage of laser radiation through a measuring cell is possible only for sufficiently high concentrations of boric acid of the order of tenths of a gram per one liter of coolant and higher concentrations (0.1-100 g / l). To measure lower values of the concentration of boric acid according to formula (5) and the classical measurement method, it is necessary to increase the length of the measuring cell L, or to increase the transverse dimensions of the cell and use several radiation passes through a multi-way measuring cell. These methods of increasing the sensitivity of the absorption spectral method used are unacceptable for a measurement system designed to operate in a nuclear reactor, as noted above. Therefore, to solve the problem of increasing the sensitivity of the measuring system under the operating conditions of a nuclear reactor in the proposed embodiment of the measuring system, we used the multiple passage of the measuring (probing) laser radiation through the measuring cell 2 by arranging feedback of the output of the measuring cell 2 with its optical input through a number of optical elements, such as this is shown in FIG. 1. The specified optical feedback is organized as follows. Laser radiation that passed once through the measuring cell 2 from the output of the fiber adapter 33 is reflected from the reflective mirror 26 of the third optical switch 25, then it is reflected from the reflective mirror 43, reflected from the translucent mirror 45 in its lateral direction, reflected from the reflective mirror 42 and translucent mirror 11 in its lateral course. Next, the laser radiation after reflection from the reflective mirror 13 of the first optical switch 12 through the first controlled attenuator 14 is fed to the input of the fiber adapter of the first fiber-optic line 28, and then is supplied a second time to the optical input of the measuring cell 2. Thus, the loopback optical communication through the measuring cell 2. The laser pulse from the output of the LI 22 modulator, once launched into the optical system through a translucent mirror 11, enters the optical feedback ring with ideally and will repeatedly circulate along this ring until the pulse is completely absorbed in the optical elements and in the measuring cell 2. In this case, at each revolution along the optical ring, a part of the laser pulse is branched by a translucent mirror 45 in the forward direction to the input of the photodetector unit 4 and is measured and recorded in control unit 6, as described above. After the branch of the laser pulse circulating in the optical ring with the help of a translucent mirror 45 in its forward direction, this pulse is fed to the input of the photodetector unit 4 after reflection from the reflective mirror 24 of the second optical switch 23 and through a controlled spectral filter 27, as discussed above . In this case, the optical switch 23 is set to transmit radiation from the measuring cell 2 (from the translucent mirror 45) to the controllable spectral filter 27 and the photodetector 4, as shown in FIG. 1. Thus, using the introduced feedback, the initial laser pulse is repeatedly transmitted through the measuring cell 2 with a fixed limited length of the working zone of the cell L. As a result, the physical path of the laser radiation pulse through the test substance of the cell increases at each revolution of the PI pulse along the feedback ring optical communication. When N turns the radiation pulse through the feedback ring, its path traveled in the substance of the measuring cell increases by a factor of TV and amounts to NL. Accordingly, the laser pulse recorded in the photodetector unit 4 after passing N times through the optical feedback ring through the measuring cell 2 will be attenuated exp (NLKC) times due to the multiple passage through the measuring cell 2 (N-fold passage) according to the formula ( 4), which determines the attenuation of the laser pulse during a single passage through a layer of a substance of length L, with a concentration C, and an extinction coefficient K. Thus, when performing multiple passages the probe laser pulse through the measuring cell 2, the equivalent effective length L of the measuring cell increases by N times and becomes equal to the value NL, which provides a corresponding increase in the sensitivity of the process of measuring the concentration of boric acid in the composition of the coolant flowing through the measuring cell 2. In order to determine concentration C of boric acid according to the formula (5), it is necessary to take into account the attenuation of laser radiation at each passage of the LI pulse along the optical ring feedback. The attenuation of the laser pulse as it passes through the feedback ring occurs due to absorption of radiation in the optical elements, primarily in the first and second fiber optic lines 28 and 31 and in the fiber adapters 30, 29, 32, 33. Such absorption (attenuation) of the laser emissions can be quite small, but with multiple passage they must be taken into account. Then, at each revolution of the laser pulse, it branches off using a translucent mirror 45 to the photodetector unit 4, as a result of which a part of the laser pulse passes further to the reflective mirror 42. Part of the energy of the laser pulse is lost on the translucent mirror 11, which plays the role of an optical adder and through which radiation of the probe laser pulse is introduced into the optical feedback ring and into the measuring cell. Additionally, a fixed predetermined attenuation is introduced into the feedback optical ring using the first controlled attenuator 14, which serves to equalize the attenuation of laser radiation in the measuring 2 and reference 3 cuvettes, which will be shown below. It should be noted that the attenuation of the laser radiation circulating along the feedback ring in the translucent mirrors 45 and 11 can be made quite small by reducing the branching fraction of the laser radiation in the forward stroke of the translucent mirror 45 towards the reflective mirror 24, and by increasing the magnitude laser radiation reflected by a translucent mirror 11 towards the reflective mirror 13. Let us denote the transmittance of the laser radiation for one of its revolution of propagation along the optical ring in the measuring cell 2 symbol T _1. Here, index 1 means that it belongs to the measuring cell 2. We consider the direction of motion (propagation) of the laser pulse clockwise from the translucent mirror 45. In this case, the coefficient of branching of the laser pulse by the translucent mirror pos. 45 to the input of the photodetector unit 4 (to the reflective mirror 24) we denote the symbol T ₄₅ . Accordingly, we denote the transmittance by the translucent mirror 11 of the probe laser radiation from the laser radiation modulator 22 towards the reflective mirror 13 (onto the optical ring) by T ₁₁ . Hence, the magnitude (energy) of the laser pulse recorded by the photodetector unit 4 (excluding the transmission of the controlled spectral filter 27), after N-times passing through the optical feedback ring, can be represented in the following form:

Here, the value of I ₀₁ is the magnitude of the laser pulse from the output of the laser modulator 22, taking into account the transmission in translucent mirrors 9 and 10. This transmission of translucent mirrors 9 and 10 can be taken into account in the transmission value T _{11 of the} translucent mirror 11. Then in formula (6) instead of I ₀₁ you can immediately substitute I ₀ .

The presented ratio most fully reflects all the factors affecting the characteristics of the laser probe pulse, which passed N times through the optical feedback ring and is detected by the photodetector unit 4. This ratio allows one to determine the desired concentration of boric acid C in the coolant based on measurements of the amplitude of the laser pulse I (N), and the detected measured photodetecting unit 4 and the measurement values of the laser pulse I ₀ T _11, piped optical feedback ring once. The magnitude of the laser pulse I ₀ from the output of the laser modulator 22 is measured using the unit for measuring the parameters of the laser radiation 20. The transmittance T _{11 is} known as the technical parameter of the translucent mirror 11.

From relation (6) it is seen that the sensitivity of the implemented measurement procedure increases in accordance with the increase in the effective length of the measuring cell by N times. This allows the measurement of low concentrations of boric acid C in the composition of the coolant of a nuclear reactor. In relation (6), only one quantity is unknown - the concentration of boric acid C, which can be determined from relation (6) by solving the corresponding equation. The concentration value C based on the solution of equation (6) can be represented as follows:

Compared with relation (5) from (7), it can be seen that in the new measurement method with an increase in N times the number of passage of laser radiation through the measuring cell 2, it becomes possible to measure N times lower concentrations C of the studied substance of the coolant flowing through the cell 2 (first component in the formula (7)). At the same time, under the sign of the logarithm, in addition to the ratio of the measured laser pulses, a multiplier appears before and after the measuring cell I ₀ / I (N)

which indicates a decrease in the level of laser pulsed radiation (signal) entering the photodetector unit 4 with an increase in the number of passes of a given probe pulsed radiation by N times. This is a natural consequence and payment for the higher sensitivity of the method being implemented (technology for measuring the concentration of C). However, it seems that this fee for high sensitivity is not too high, since currently there are sufficiently powerful laser generators in the UV wavelength range and highly sensitive UV photodetectors (PMTs), using which the indicated decrease in the laser pulse value in the proposed measurement system in accordance with the given value, R (8) can be compensated and is not significant. Consider again the relation (7) to determine the concentration C with a single pass of the laser pulse through the measuring cell 2, at which N = 1:

where R ₁ = T ₁₁ T ₄₅ T ₁ . According to (8), R is equal to R ₁ at N = 1. In this single pass of the laser pulse through the measuring cell, relation (9) coincides with the basic formula for calculating the concentration C (5), given that the transmission of translucent mirrors pos. 11 and 45 T ₁₁ T ₄₅ were taken into account when outputting (5) during the measurement of the value of the laser probe pulse in the unit for measuring the parameters of laser radiation 20, and when measuring the laser pulse transmitted through the measuring cell, in the photodetector unit 4. The attenuation value T _{1 of the} laser pulse at a single pass at the output (5) was assumed to be equal to 1 and was omitted. Thus, relation (9) is a more accurate formula for calculating the concentration of C in one pass compared to the standard formula (5) due to the additional technical parameters of the elements of the optical circuit of the measuring system. The transmission parameters of optical elements R ₁ = T ₁₁ T ₄₅ T ₁ in (9) are, in principle, known values and do not change during the measurement of concentration C. However, these parameters affect the final result, and during the measurement, the value of these parameters must be accurately known and remain unchanged to ensure high accuracy and sensitivity of measurements of low concentrations of boric acid. Therefore, to achieve high accuracy of measurements at low concentrations of the measured substance in the proposed measuring system, a number of means were used aimed at measuring and stabilizing the indicated parameters R included in the main formula for determining the concentration C (7). Such means include the use of a reference cell and the use of a second laser generator 8. The reference cell 3 is a complete analogue of the measuring cell 2, but is located together with the main measuring equipment in a separate room, protected from the effects of radiation from a nuclear reactor. The reference cell 3 is provided with fiber optic lines 34 and 37 with fiber adapters similar to a measuring cell. In this case, the fiber lines 34, 37 in the reference cell 3 have the same length as the fiber lines 28 and 31 in the measuring cell 2. Fiber lines 28 and 34, providing a probing laser pulse to the inputs of the measuring and reference cell, are connected in the same way to optical inputs of the first optical switch 12 through the first 14 and second 16 controlled attenuators. Accordingly, the optical outputs of the measuring and reference cuvette are connected in the same way via fiber lines 31 and 37 to the optical inputs of the third optical switch 25. The reference cuvette 3 is equipped with a working substance filling unit 49. The operator, through this unit 49, fills the reference cuvette 3 with boric acid solution in distilled water necessary (predetermined) concentration C _et . As a result of this, in testing mode, it is possible to fully and accurately simulate the operation of the entire measuring system when measuring any given concentrations of C _et boric acid in a reference cuvette under conditions and with the length of the connecting fiber-optic lines similar to those used in the measuring cuvette. The difference is only in the absence of radiation in the zone where the reference cell is located 3. To implement the test mode in the proposed measurement system, a control signal is supplied from the control unit 6 to the first 12 and third 25 optical switches to switch the optical system to the connection position of the reference cell 3 instead of the measuring cell 2 According to this signal, the optical switches 12 and 25 rotate 180 degrees of reflective mirrors 13 and 26, as a result of which the laser radiation from a translucent The mirror 11 enters through the second controlled attenuator 16 to the fiber adapter 35 and then through the fiber line 34 to the input of the reference cell 3. Accordingly, the optical output of the reference cell 3 through the fiber line 37, the fiber adapter 38 and the reflective mirror 26 in its new position enters the reflective mirror 43. Thus, a reference cell 3 is included in the annular optical system instead of the measuring cell 2. In FIG. 7 shows the position of the first optical switch 12 in the state of inclusion of the reference cell in the optical measuring system and the corresponding position of the reflective mirror 13. Next, the concentration of the substance in the reference cell 3 is measured in the measuring system in the same way as shown above when measuring the concentration in the measuring cell 2 In this case, a laser probe pulse is supplied to the input of the reference cell 3 and reception and registration of laser pulses from the output of the reference cell 3 using photodetector unit 4. The signal processing results output from the processing unit 5 receives a control unit 6, which is carried out storing the acquired information.

An additional measuring tool is the newly introduced second laser generator 8. This laser generator operates at a wavelength that lies in the blue-green part of the visible wavelength range at which the extinction coefficient K of the boric acid solution decreases to zero. This means that the optical absorption properties (optical density) of a solution of boric acid of any concentration are identical to the optical properties of pure distilled water without boric acid. This allows you to test and determine the transmittance of the measuring cell and the optical elements connecting it without pumping out the working medium of the coolant from the measuring cell. Thus, testing and verification of the main optical parameters of the measuring cell and connecting elements can be carried out in the operating mode of a nuclear reactor by simply connecting a laser generator operating at a different wavelength. In practice, the transition to this test mode is carried out by turning off the main first laser generator 1 and turning on the second laser generator pos. 8, as well as by turning on the corresponding laser radiation modulator 21. In this case, the laser pulse from the laser generator 8 will be transmitted to the reflective mirror 13 in the optical system. It should be noted that when the measuring system is in test mode with the second laser generator at a new wavelength laser radiation controlled spectral filter 27 is tuned to filter the laser radiation with this new wavelength on command from the control unit 6.

We list the main operating modes of the first version of the proposed system for measuring the concentration of boric acid in the coolant of a nuclear reactor, starting from the test mode of the measurement system.

1) At the first stage, the measuring system is operated on a reference cell 3 when this cell is filled with pure distilled water without the presence of boric acid. In this case, the first 12 and third 25 optical switches are set to the position of connecting to the measuring system of the reference cell 3, in contrast to that shown in FIG. 1, where a measuring cell 2 is connected to the measuring system. At this first stage, the second laser generator 8 is operating, and the first laser generator 1 is turned off. The laser radiation modulator 21 generates one probe laser pulse at the wavelength of the laser generator 8. Next, this LI pulse enters through the translucent mirror 11 into the optical feedback ring, including the reference cuvette 3, and begins to circulate along this ring, similar to how it was discussed above for measuring cell 2. In this case, the photodetector unit 4 receives and registers laser pulses at each revolution of the radiation along the ring. Information on the parameters of these pulses from the first to a certain pulse with the number N is recorded in the control unit 6, as was discussed above. When taking measurements at the wavelength of the laser generator 8, the controllable spectral filter 27 switches to filtering and transmitting the corresponding wavelength.

2) At the second stage, the measurement process with the reference cell 3 is carried out at the wavelength of the first laser generator 1, and the laser generator 8 is turned off. The controlled spectral filter 27 is switched to the filtering mode of the laser radiation at the wavelength of the first laser generator 1. The reference cell 3 is still filled with pure distilled water. The photodetector unit 4 registers a series of laser radiation pulses at the working wavelength of the first laser generator 1, which are then stored in the control unit 6.

3) At the next two stages, measurements are taken with a reference cell 3 when it is filled with a solution of boric acid in distilled water with a certain selected concentration of C ₀ , for example, one milligram per liter. The filling of the reference cuvette 3 is carried out by the operator using the filling unit 49. Next, a series of laser pulses is recorded at the wavelength of the laser generator 8, which passed through the optical feedback ring a certain number of times to some last specified number N.

4) At the fourth last stage of work with the reference cell 3, measurements are taken at the wavelength of the first laser generator 1, as was done in stage 2.

As a result of measurements of boric acid with a reference cell 3 in the control unit 6, information is generated on the parameters of a series of laser pulses transmitted through the reference cell 3 a different number of times from one to a certain final number N. Moreover, the concentration of boric acid in the reference cell 3 is precisely known and equal to C ₀ , and the measurement of the levels of laser pulses was carried out for two known wavelengths - the working wavelength of the first laser generator 1 and the wavelength of the second laser generator 8. Thus, with Using the reference cell 3, the process of measuring the concentration of boric acid С ₀ under the conditions coinciding with the measurement conditions in the measuring cell 2 with respect to the optical scheme and optical signals — laser pulses was completely modeled.

Next, the measurement system goes into the measurement mode with the measuring cell 2. To implement this mode, the optical switches 12 and 25 are set to connect the measuring cell 2 to the optical measuring circuit, as shown in FIG. 1. Then, at the first stage of work with the measuring cell 2, measurements are carried out (as with the reference cell) at the wavelength of the second laser generator 8, and the first laser generator 1 is in the off state. A series of laser pulses is received and registered, which passed through the optical feedback ring through the measuring cell a certain number of times to the maximum number N. Moreover, the optical properties of the measuring cell 2 and the reference cell 3, as well as the supply elements, are the same, since the laser generator 8 operates at a wavelength in the blue-green region of the spectrum, in which the extinction coefficient of boric acid is zero, as a result of which boric acid in the measuring cell does not introduce additional absorption into th pulse of laser radiation. Therefore, the parameters of the set of laser pulses recorded at this stage of the measurements using the measuring cell must coincide with the same set of pulses recorded in block 6 in step 1 of the measurements with the reference cell 3 (see above). In control unit 6, the indicated groups of laser pulses stored in block 6 are compared, and with a small difference in amplitude, the transmitting in the feedback ring, including the measuring cell 2 with the same transmitting along the ring with the reference cuvette 3. The adjustment criterion is the coincidence of the amplitudes of the pulse groups with the corresponding numbers of passage along the feedback ring for the measuring and reference cuvettes when testing measurements at the wavelength of the second laser generator 8.

Next, the main stage of measurements with a measuring cell 2 is carried out when the laser generator 1 is operating at its working wavelength and registration of the values of laser radiation pulses at this wavelength that have passed a certain number of revolutions along the feedback ring, as discussed above. The resulting set of impulse values I (N) is then used to calculate the concentration of boric acid according to the formulas given above. In this case, various algorithms for calculating and determining the parameters of the coolant can be used using information about the measurements taken with the reference cell 3 stored in the control unit 6.

It should be noted that calibration and reduction to a single measurement scale of the characteristics of the photodetector unit 4 and the unit for measuring the parameters of laser radiation 20 at two wavelengths of the first 1 and second 8 laser generators are carried out separately, as described above. During this calibration, the second optical switch 23 is translated into the position of the input to the input of the controlled spectral filter 27 of laser pulses from the reflective mirror 50. This calibration can be carried out separately before or after the main measurements. It should be noted the main requirement for the duration of laser pulses generated by laser modulators 21 and 22, circulating along the optical feedback ring. The duration of the laser pulse should not exceed at least half the time of revolution of the pulse along the optical feedback ring. If the duration exceeds the specified value, the pulses will merge, which will complicate their separation and determination of the amplitude of each individual pulse. We define the requirements for the duration of laser pulses for a standard arrangement of measuring equipment 25 meters from a nuclear reactor. The length of the feedback ring will be 50 meters, and the length of one fiber-optic line will be 25 m. The time of one turn around the ring will be 1.6 μs. Under these conditions, the laser pulse duration should not exceed 0.8 μs. A laser pulse with a duration of 0.5 μs can be successfully used to separate individual revolutions along the feedback circuit in the proposed measuring system for the specified length of the used fiber optic line, which in the proposed measuring system performs the second function of the delay line of laser pulses for their separation by time for the purpose of separate registration.

In the first version of the construction of the measurement system considered, to increase the measurement sensitivity, the method of multiple passage of the probe laser pulse through the measuring cell 2 was used. In this case, the laser pulses are separated by the time of their arrival using a fiber line, which not only provides a remote location of the measuring equipment at a certain distance from a nuclear reactor, but also performs a second function - the function of the delay line needed to partition impulses according to the time of their arrival.

In the second version of the construction of the measuring system, another method for separating laser pulses is used, based on the frequency coding of laser pulses that have passed a different number of revolutions along the optical feedback ring, including a measuring cell. A block diagram of a second embodiment of a measurement system is shown in FIG. 2. The main optical elements of the second embodiment of the measurement system in FIG. 2 coincide with similar optical elements of the first embodiment in FIG. 1, perform the same functions and are denoted by the same numbers as similar elements in FIG. 1. The difference in the block diagrams of FIG. 2 and FIG. 1 is as follows. In the second version of the measurement system excluded modulators of laser radiation pos. 21 and 22 in FIG. 1. Furthermore, in the circuit of FIG. 2 instead of a reflective mirror pos. 50 in FIG. 1, a translucent mirror 51 is introduced, which is installed in the optical circuit exactly at the location of the reflective mirror 50 in the first embodiment of the circuit of FIG. 1. At the same time, the new translucent mirror 51 (sixth translucent mirror) also performs the function of the previous reflective mirror 50 and directs the laser beam from the reflective mirror 41 to the reflective mirror 24 of the second optical switch 23. Two new elements in the second embodiment of the measurement system in FIG. 2 are the newly introduced first (pos. 52) and second (pos. 53) laser frequency shift blocks. The first block of the frequency shift of the laser radiation 52 is connected by its optical input to a new translucent mirror 51. The optical output of the frequency shift unit LI 52 is optically connected to the optical input of the lens 7 of the photodetector 4 by means of the newly introduced sixth reflective 54 and seventh translucent 55 mirrors. Through the frequency shift unit 52, part of the radiation from the laser generators 1 and 8 is directed to the input of the photodetector unit 4. These laser radiation with a shifted frequency perform the functions of heterodyne laser radiation. The second laser frequency shift unit 53 is mounted in the optical feedback ring between the reflective mirror 42 and the translucent mirror 11. The control electrical inputs of both LI frequency shift units (c1 and c2) are connected to the control unit 6. The LI 53 frequency shift unit carries out a frequency shift of the transmitted through it along the ring of optical feedback of the laser radiation (laser pulse) by a predetermined fixed amount of shift F. Moreover, for each revolution of the laser radiation along the ring of optical feedback to a fixed value of F is added to its optical frequency. Thus, the laser radiation that has made N revolutions along the feedback ring will have an additional optical frequency shift equal to NF compared with the initial laser radiation from the output of laser generator 1 or laser generator 8, depending from which laser generator is working at a given time. The difference in the values of the additional shifts of the optical frequency acquired by the laser radiation depending on the number of revolutions along the feedback optical ring is used to separate these laser radiations (LI pulses) when receiving and recording these radiations and processing them in the photodetector unit 4, as well as in the unit signal processing 5 and in the control unit 6. The photodetector unit 4 in this second embodiment of the measurement system in FIG. 2 operates in the mode of laser heterodyne reception of incoming laser radiation - in the mode of so-called photo-mixing. In this case, the first frequency shift unit LI 52 performs the function of forming laser heterodyne radiation (signal) with a given optical frequency. The optical input of the photodetector unit 4 receives laser radiation having an optical frequency with a shift of NF after passing Ν revolutions along the optical feedback ring, as well as laser heterodyne radiation from the output of the first frequency shift unit LI 52, which has a frequency shift established by the control signals from the block control 6 and equal to the value of NF + F _CR , where the value of F _CR is some additive, set also by the signals from the control unit 6 and equal to the value of the transmission frequency (filtering) of the electric fil тра of the intermediate frequency in the signal processing unit 5. The photodetector unit 4 registers a beat signal between the received laser radiation with a frequency shift equal to NF and the local oscillator laser radiation from the output of block 52 having a LI frequency shift equal to the sum of NF + F, _etc. The beat frequency of the resulting electrical signal is equal to F _CR and represents the difference in the optical frequencies of the indicated laser radiation supplied to the input of the photodetector unit 4. Next, the electrical signal from the output of the photodetector unit 4 is amplified in the signal processing unit 5 by a resonant amplifier with an intermediate frequency filter frequency equal to F _pr , enters the demodulator, where its amplitude is determined, then after digitization it enters the control unit 6 for further processing and storage.

When changing the magnitude of the shear frequency of the laser radiation in the first block of the frequency shift LI 52 and at a constant value of F _{pr it} is possible to receive and register laser radiation that has passed through the optical feedback ring for a given number of revolutions. For example, when setting in the frequency shift unit LI 52 the value of the frequency shift LI equal to (N + 1) F + F _CR by commands from the control unit 6, in the photodetector unit 4 and the signal processing unit 5, reception and registration of laser radiation transmitted along the optical feedback ring N + 1 revolutions and having an optical frequency shift equal to (N + 1) F, where F is equal to a constant shift of the laser radiation frequency in the second frequency shift unit LI 53 in one pass of the laser radiation through this block 53. B the result in the control unit 6 naka Lebanon, and records information about the values of the laser (pulse) amplitudes, past a certain number of turns from one turn to N rotations of the ring optical feedback, as carried in the first embodiment, the measurement system build. Otherwise, the principle of operation of the second version of the measurement system is similar to the functioning of the first version of the measurement system. The process of receiving and registering a set of laser signals that have passed a different number of revolutions is recorded separately for each of the laser generators that operate, as in the first version of the measurement system, alternately.

However, in this embodiment of the construction of the measurement system, the simultaneous operation of two laser generators 1 and 8, and the simultaneous registration of sets of laser radiation that have passed a certain number of revolutions along the feedback ring at different wavelengths of laser radiation generated by laser generators 1 and 8. Accordingly, controlled spectral the filter 27 in this case is transferred to the filtering and transmission mode of two optical wavelengths of the first and second laser generators simultaneously.

The blocks for shifting the frequency of laser radiation are made on the basis of acousto-optic cells, in which the ultrasonic waves interacting with the transmitted laser radiation are excited, as a result of which the optical frequency of the laser radiation is shifted by the frequency of the ultrasonic wave. The width of the spectrum of laser radiation generated by the laser generators 1 and 8 imposes certain requirements on the magnitude of the frequency shift of the laser radiation in the frequency shift unit LI 53 included in the optical feedback ring. The frequency shift realized in the shift block 53 should be greater than the width of the spectrum of the generated laser radiation in laser generators 1 and 8. This is necessary to separate the laser signals that have passed a different number of revolutions along the optical feedback circuit. At present, gas laser generators exist and are manufactured by industry, which have a very narrow band of generated laser radiation and are used as optical local oscillators. The photodetector unit 4 and the signal processing unit 5, including one or more resonant amplifiers for amplifying the intermediate frequencies of the beats of optical (laser) radiation, are standard means of a heterodyne method for receiving laser radiation having optical frequency shifts relative to the initial frequency of the generated laser radiation. The use of frequency coding of pulses (signals) of laser radiation along the optical feedback circuit has some advantages over the first version of the construction of a measurement system. Such advantages include a higher sensitivity of the heterodyne method of receiving laser radiation, which allows the use of a larger number of revolutions of the probe laser radiation along the optical feedback ring, which in turn significantly increases the sensitivity and the ability to determine very low concentrations of the studied substances. When using the frequency method of encoding laser signals, there is no need to use a special optical delay line, which allows you to place the measuring equipment close to the observed object in the absence of radiation.

Consider the question of the possibility of measuring low concentrations of boric acid in the proposed measurement system. This consideration is equally true for the first and second options for constructing a measuring system. As noted above, the measurement of the concentration of boric acid C in the measuring cell 2 is based on six consecutive stages of preliminary measurements of the parameters of the sets of values of the laser pulses transmitted through the measuring cell and the pulses transmitted through the reference cell using the radiation of the first laser generator at the operating wavelength, and also a second laser generator operating at a second wavelength in the blue-green region of the spectrum, at which the extinction coefficient of boric acid is zero, which It allows one to determine the transmission parameters of the measurement and reference cuvettes. In addition, the parameters of the reference cell at the indicated two wavelengths are determined by filling this cell with pure distilled water and a solution of boric acid in distilled water with a known concentration set by the operator. It is also possible to change the concentration of boric acid solution in the reference cuvette during any measurement by any specified value set by the operator. As a result of these measurements and storing in the control unit of 6 sets of values of laser pulses, it is possible to implement various algorithms for processing the obtained information and various measurement procedures that provide measurement of very low concentrations of boric acid and increase the accuracy of measurements and the reliability of the results.

Consider the measurement of the concentration of boric acid, carried out, as was shown above, by registering the level of the laser pulse at the working wavelength of the first laser generator, which passed through the measuring cell N times and made, respectively, N revolutions along the feedback ring. After registering the LI pulse, based on the magnitude of the amplitude of this pulse I (N) recorded in the control unit 6, the concentration C of boric acid in the coolant circulating in the measuring cell 2 is determined by the basic formula (7). When calculated by the formula (7) well-known and previously calculated values are the coefficient of extinction of boric acid K at the wavelength of the laser generator 1, the length of the measuring cell L and the used number N of revolutions of the laser pulse along the optical return ring communication. The measured values are the value of the level of the initial probe laser pulse I ₀ , measured using the measuring unit of the laser radiation parameters 20 and the magnitude of the laser radiation pulse I (N), passed N times through the optical feedback ring and detected by the photodetector unit 4. The indicated laser pulses are measured using blocks 20 and 4 with high accuracy provided that modern high-sensitivity photodetectors included in these blocks are used and sufficiently high levels of radiation energy in the recorded radiation pulses I (N) and I ₀ arriving at the optical inputs of these photodetectors.

The latter is quite simple and reliable when using modern, sufficiently powerful UV laser generators and highly sensitive laser photodetectors - UV PMTs. The composition of formula (7) also contains the value of R (8), which is determined by the transmission of optical elements in the optical feedback ring at the working wavelength of the first laser generator 1 with a measuring cell. This component is determined with high accuracy using a reference cell as follows. Initially, the reference cell 3 is filled with distilled water. The levels of laser pulses are measured at the wavelength of the second laser generator 8 with the number of revolutions N, individually when these pulses pass through the measuring and reference cuvettes and the values of these pulses are equalized using the first and second controlled attenuators 14 and 16. This ensures equalization of the transmission of the optical ring feedback when the measurement cell is turned on, and when the reference cell is turned on. Next, the reference cuvette 3 is illuminated with laser radiation at the working wavelength of the laser generator 1 and the laser pulse I _{0 et} (N) is _recorded for the reference cuvette 3 filled with distilled water, as noted above (the component “O” here means filling cuvette 3 water, and the component "et" means a reference cell). In this case, at a zero concentration of boric acid in the reference cell 3, the detected laser pulse at the working wavelength is equal to (3)

Hence, the desired value of R for calculation by formula (9), the concentration value C is equal to:

Thus, the R value for calculating C by formula (7) was obtained by measuring the transmission in the reference cell 3 for a laser pulse at the working wavelength when filling the reference cell with distilled water. In this case, in the magnitude of the laser pulse (10), which passed through the reference cell N times, there is no component determined by the concentration of boric acid, since the reference cell is filled with distilled water. In this case, component R (11) is equal to the corresponding component R (8) for measuring cell 2, since the optical transmittance for the measuring and reference cuvettes was higher by radiating the cuvettes with laser radiation with a wavelength of the second laser generator 8. The obtained value of R (11 ) allows you to calculate the concentration of boric acid in the following form when substituting the value of R (11) in the main ratio to determine C (7):

Formula (12) determines the desired concentration of boric acid in the form of a ratio of known and measured physical quantities. In formula (12), due to the use of measurement in a reference cell 3, which in this embodiment of the measurement procedure is an analogue of a measuring cell 2, but without boric acid, the optical system parameters of the optical feedback ring are excluded. The measured values are the amplitude of the laser pulse I _0et (N) passed through a reference cell with distilled water with the number N of revolutions along the feedback ring and the amplitude of the laser pulse I (N) passed through a measuring cell with boric acid of the desired concentration C and number revolutions along the feedback optical ring is also equal to N. These laser pulses are measured by the same photodetector unit 4 under the same conditions, as shown above. The accuracy of the measurements of these laser pulses can be quite high when using modern highly sensitive UV photodetectors and relatively powerful laser generators. The adjustment of the parameters of the measuring and reference cuvettes and the compensation and elimination of the influence of transmission of the elements of the optical circuit when connecting the measuring and reference cuvettes allows to increase the accuracy of measurements of small concentrations of boric acid in the composition of the coolant in the measuring cell 2.

As can be seen from (12), the possibility of measuring low concentrations of boric acid C is determined by the level of attenuation (decrease) of the laser pulse when passing through the optical feedback ring, I (N). This attenuation, as was shown above, is proportional to the exp (KCLN) value, which increases with an increase in the number of revolutions N. This proves an increase in the possibility of measuring low concentrations and an increase in the measurement accuracy when using the proposed measurement method with the multiple passage of the probe laser radiation through the measuring cell along the optical ring feedback. Additionally, the accuracy of the measurements and the reliability of the information obtained about the concentration C can be increased as follows. The reference cuvette 3 is filled with a boric acid solution with a concentration C equal to that measured and calculated according to formula (12) of concentration C in the measuring cuvette 2. This operation is performed by the operator using the filling unit 49. Next, the concentration of boric acid in the reference cuvette 3 is measured as described above. using laser radiation of the first laser generator 1 and the calculation according to the formula (12). The result obtained for a reference cuvette filled with boric acid with a precisely known concentration equal to the concentration C measured previously in the measuring cuvette is compared with the result of measurements in the measuring cuvette 2. The comparison is carried out according to the levels of laser pulses I (N) measured by the photodetector unit 4 for measuring and reference cell.

The coincidence of the values of the indicated laser pulses that have passed the same number of revolutions N along the feedback ring for the measuring and reference cuvettes will indicate a high accuracy and reliability of the obtained measurement results. With a slight difference in the obtained pulse values, it is possible to repeat the measurements with the additional equalization of the transmission of optical elements in the feedback ring when a measuring or reference cell is connected to the feedback ring. It should be noted that an important advantage of the proposed photometric method and measurement system compared to the well-known chemoluminescent measurement method is the possibility of repeated repetition and verification of measurements without secondary complex sampling from the coolant circuit using the chemoluminescent method. The need for additional and secondary measurements may arise in the case of obtaining measurement results that differ from the expected results, as well as in the event of emergency situations. In this regard, various options and measurement techniques that can be implemented using the proposed measurement system are of great importance. Let us consider one of the additional options for measuring the concentration of boric acid, based on measuring the amplitudes of laser pulses I (N), which have passed N revolutions along the optical feedback ring, the amplitude of which is determined by relation (6). As noted above, in the control unit 6, when taking measurements with a measuring cell 2 at the working wavelength of the first laser generator 1, information is stored on the set (series) of amplitudes of laser radiation pulses transmitted through the optical feedback ring at different speeds, increasing from one revolution up to N revolutions. The amplitude of the pulse that has passed one revolution (N = 1) is, according to (6), the value:

When dividing (6) by (13), we obtain the following relation, in which the parameters of the optical scheme are excluded, except for transmitting radiation along the feedback ring T ₁ :

Thus, by measuring the amplitude of the first laser pulse with the number N = 1 and the laser pulse with the number N, it is possible to determine the concentration C from relation (14) using the following formula:

In relation (14), there is only one optical parameter T ₁ , which determines the transmission of optical radiation through the feedback ring per revolution. This value can be calculated with a high degree of accuracy for the reference cuvette and extended to measurements in the measuring cuvette using equalization and transmission control of both cuvettes at the wavelength of the second laser generator. Relation (15) shows that the concentration C can be determined by comparing any two pulses of laser radiation having a known difference in the past revolutions along the feedback ring, i.e. having a known difference in the distance traveled through the layer of the measured substance. In the case of the first and Nth pulses, the difference in the number of revolutions is Ν-1. Moreover, in (15), the transmittance T ₁ along the optical feedback ring to the degree of the number of revolutions along the ring N is taken into account and compensated. When transmitting is equal to unity, i.e., in the absence of absorption in the feedback ring, the measurements become ideal, and in the formula ( 15) only the values of the measured amplitudes of the laser pulses that have passed a different distance and the number of revolutions along the feedback ring are present. Thus, the described method for determining the concentration of C by the formula (15) is a good addition to the previously described methods for determining the concentration in the proposed measuring system. According to this method and relation (15), after registering in the control unit 6 the set of laser pulses I (N) that passed through the measuring cell and made one to N revolutions along the feedback ring, in block 6, the corresponding estimate of the concentration C is calculated, which can be made for each registered laser pulse, starting with the second pulse. Analysis of the obtained set of C concentration estimates together with the obtained C estimates by another method described above will improve the accuracy of measurements and the reliability of the information received. It should be emphasized once again that the accuracy of determining the transmission parameter Τ ₁ along the feedback ring can be made extremely high. The second and last factor affecting the accuracy of determining the concentration. This method is the accuracy factor for determining the ratio of the amplitudes of the laser pulses by the photodetector unit 4. This accuracy is determined by the parameters of the photodetector included in the photodetector unit 4. Currently, there are photodetector devices operating in the UV range (up to 200 nm) having a high sensitivity of the order of units of photons in the received laser pulse [11]. To achieve high accuracy of measurements using these photodetector devices, it is necessary to ensure the formation of measured laser pulses with an energy in pulse exceeding the level of intrinsic noise and fluctuations of this photodetector by 10 times or more. When using a laser generator of the UV range of the appropriate power, achieving a mode of exceeding the threshold sensitivity level of modern PMTs and realizing high accuracy in measuring pulse amplitudes of the order of one percent of the measured amplitude is quite achievable and does not present major technical problems.

Further, we consider the question of determining small concentrations of boric acid in the coolant circuit using the described measurement procedure in the proposed measuring system. The determination of the concentration of boric acid in the measuring cell 2 is based on relation (7), which takes into account all the factors affecting the measurement process. To measure the concentration of C according to this formula (7), it is necessary to record the value of the laser pulse I (N), which passed through the optical feedback ring N revolutions. The amplitude of this pulse after passes N is determined by the value of the probe laser pulse I ₀ , the parameters of the optical scheme, transmission of N passes through the feedback ring and absorption of radiation when passing through a solution of boric acid with the desired measured concentration of C. (see formula 6). The last component of absorption, as was noted, is proportional to the value of exp (KNLC). Relation (6) allows us to determine the technical requirements for the equipment of the measuring system to ensure the process of measuring specified small values of concentration C with acceptable measurement accuracy. As noted above, the value of the product KL under the exponent sign determines the sensitivity of the absorption measurement method. Therefore, an increase in the number of passes of the probe laser pulse directly increases the sensitivity of the proposed measurement method. To implement and ensure this method, it is only necessary to register and measure the laser pulse from relation (6), which has passed N revolutions in the ring, using the photodetector 4 with sufficient accuracy. For this, it is necessary to fulfill the only condition: to ensure a significant excess of the level of the received laser pulse over the level of the noise of the photodetector 4. Thus, by selecting a highly sensitive photodetector and a sufficiently powerful laser generator, it is possible to ensure high sensitivity and accuracy of measurement of small concentrations of boric acid by the proposed measurement method. Let us present an estimate of the requirements for the parameters of the laser generator and the sensitivity of the photodetector unit. We denote by the symbol E _{0 the} threshold sensitivity of the photodetector unit 4, which is, for example, three times the level of the received laser pulse above the level of the noise of the photodetector. This level is sufficient to detect a laser pulse, as is done in a laser location [7], but insufficient to accurately measure the amplitude (level) of a received laser pulse. To accurately measure the level of the laser pulse, it is necessary to increase the energy of the laser pulse by 10 or more times. Let us denote by the symbol E ₁ = nE _{0 the} level of the received laser pulse, sufficient for accurate measurement of the value of this pulse by modern technical means, for example, with an accuracy of about 10%. The value of E ₁ can exceed the level of threshold sensitivity n times, where n = 10-100. Then the value of the ratio B = I ₀ / E ₁ characterizes the potential of the measuring system in relation to the parameters of the selected laser generator and photodetector

Here, the values of I ₀ and E ₁ are measured in the number of photons in the generated pulse of the laser generator 1 (taking into account attenuation in the LI 22 modulator), as well as in the received laser pulse I (N). It is also possible to measure the values of laser pulses in units of energy per pulse. The value of B characterizes the possible (permissible) level of attenuation of the laser pulse I (N) during its multiple passage through the optical feedback ring. Hence, substituting in Eq. (6) instead of I (N) its limit value E ₁ and taking into account the relationship I ₀ and E ₁ through the indicated potential ratio B, we obtain the following ratio to determine the potential capabilities of the proposed measuring system:

Relation (16) allows for given or selected levels of potential attenuation B (16.1), the length of the measuring cell L, extinction coefficient K, and the optical system parameters T ₁₁ and T ₁ , T _{45 to} determine the possible limit number of revolutions of the probe laser pulse along the optical feedback ring connection N and the minimum concentration C of boric acid, measured in the proposed measurement system with an acceptable predetermined measurement accuracy. Based on this obtained formula, an assessment was made of the potential capabilities of the proposed measurement system for the determination of low concentrations of boric acid in the composition of the coolant. It should be noted that equation (16) cannot be solved with respect to the number of revolutions N, except by numerical methods. Therefore, the evaluation of the parameters of the measuring system based on equation (16) was carried out for the selected discrete values of the number of revolutions N in the form of the following series N = 10, 20, 30, 40. The main optical parameter of boric acid is the extinction coefficient K, which substantially depends on the wavelength passing through a layer of the test substance (boric acid H ₃ BO ₃ ) optical radiation. As noted above, boric acid has a noticeable absorption of optical radiation in the ultraviolet wavelength range. The highest absorption of UV radiation by boric acid is observed in a short part of the UV range. When the wavelength of UV optical radiation is 200 nm, the extinction coefficient K of a solution of boric acid in distilled water reaches its maximum value and is K = 1.64 × 10 ^-4 L cm ^-1 mg ^-1 . This assessment was obtained by measuring the optical parameters of boric acid, carried out on an experimental (experimental) sample of the proposed measurement system, and coincides with the reference data characterizing the properties of boric acid [17]. In the longer wavelength part of the UV range, the absorption of boric acid decreases, and at wavelengths of optical radiation of more than 400 nm, the optical properties of boric acid practically coincide with the properties (absorption) of distilled water. This excludes the possibility of measuring the concentration of boric acid using a radiation source with a wavelength of more than 400 nm, but allows you to use this radiation source to test the transmission of the optical circuit, as was shown above when using laser generator 8 in the blue-green region of the visible radiation spectrum. Therefore, for carrying out measurements of the concentration of boric acid, it is most preferable to use a laser generator of the UV range with the shortest wavelength in this range, approaching a value of the order of 200 nm.

Based on the materials of this application, an experimental (experimental) sample of a boric acid measurement system was developed and investigated, various concentrations of boric acid solutions were measured and boric acid extinction coefficient was measured for various wavelengths of probe radiation, and the operation of a boric acid measurement system in the coolant circuit was simulated, the results of which are given below. The extinction coefficient K was measured on a reference cuvette when it was filled with a boric acid solution of a previously known (prepared) concentration C _et . Next, the optical parameters of the input and transmitted optical radiation were measured. The determination of the extinction coefficient K was carried out in accordance with the basic equation (5), which was solved with respect to the unknown value of K for the remaining known and measured values. As a result, the magnitude of the extinction coefficient K was determined from the following ratio:

The following are estimates of the parameters of the proposed system for measuring the concentration of boric acid when using UV radiation with a wavelength of 200 nm and for the extinction coefficient K corresponding to this wavelength and equal to the above value K = 1.64 × 10 ^-4 l / cm ^-1 mg ^{- 1} . The estimates were carried out in accordance with relation (16) for the following parameters of the optical design: length of the measuring (and reference) cell L = 100 cm. Transmission of optical elements T ₁₁ = T ₄₅ = 0.01. Passing along the optical feedback ring in one pass T ₁ = 0.5. The number of passes N ranged from 10 to 40 passes of the probe laser radiation along the optical feedback ring.

For modeling, three values of boric acid concentration were chosen: C = 1 mg / L, C = 0.5 mg / L, and C = 0.1 mg / L. The results obtained showed the ability to measure these low concentrations of boric acid using the proposed measurement system. Further, the obtained simulation results of the parameters of the measuring system are presented for each value of the concentration of boric acid With as follows. The main parameter obtained as a result of the simulation is the parameter W, the inverse of the potential B of the optical system introduced above using a laser generator of a certain power and a photodetector block of a certain sensitivity. In accordance with formula (16), the parameter W = 1 / B determines what part (fraction) of the energy of the probe pulse emitted by the laser generator will reach the photodetector unit 4 when N turns are made along the optical feedback ring. In accordance with (16), the estimate of W is equal to:

Thus, the parameter W determines the transmission of the probe radiation from the laser generator to the photodetector unit 4 through the multiple passage of radiation along the optical feedback ring.

The parameter W consists of two parts: the values of T ₀ = T ₁₁ T ₄₅ T ₁ ^N and the values of E _p = exp (-KCNL). The value of T ₀ determines the transmission of the optical system without boric acid. The value of E _p determines the transmittance of the probe laser radiation due to absorption during passage through a layer of boric acid in the measuring cell. Both components reflect the attenuation of the probe laser radiation at N revolutions along the ring.

The value of W determines the total transmission of boric acid during the propagation of the laser probe pulse along the optical feedback ring for N revolutions along the feedback ring. In the presented results, these two components are presented separately, in order to be able to show the influence of each factor on the final result and more correctly approach the choice of parameters of the optical system. The results are presented in the form of a table. one.

The simulation results indicate the possibility of measuring low concentrations of boric acid in the concentration range C from one milligram per liter to 0.1 mg / l. At the same time, to measure concentrations from one milligram per liter (and higher) it is enough to use N = 10 revolutions of the probe laser radiation along the optical feedback ring.

So, for example, when measuring the concentration C = 1 mg1 mg / L, the value of E _p is at ten revolutions along the feedback ring E _p = 0.848, which indicates a decrease in the measured laser pulse I (N), which has passed N revolutions along the optical feedback ring communication by 15% compared with the value of the level of the laser pulse at zero concentration C = 0 of boric acid. The value of E _p is equal to the ratio of the values of the measured laser probe pulses by the photodetector unit 4 in the presence of a concentration of C = 1 mg / l and at C = 0, E _p = I (N) / I ₀ (N). Such a change (decrease) in the level of the magnitude of the laser pulse (15%) is quite sufficient to determine and measure the concentration of C from 1 mg / l and higher. When using the value N = 20 revolutions, the change in the level of the laser pulse at a concentration of C = 1 mg / L is 28% (E _p = 0.72), which significantly exceeds the required level for high-precision measurement (about 3-5%). To implement these values of the revolutions N = 10 and 20, it is necessary to register the laser pulse after attenuating the radiation from the laser generator to levels 10 ^-6 and 10 ^-9, respectively (see the value of W in the right column of Table 1 for concentrations C = 1 mg / l

This condition for receiving and recording laser radiation is fulfilled using modern PMTs of the UV range and a laser generator with a very low energy of the order of one microjoule in the emitted pulse [11]. The corresponding power at a repetition rate of 1 Hz is equal to one microwatt. Similarly, in the measuring system, the boric acid concentration C = 0.5 m / l is confidently recorded and measured, for which, at N = 10 rpm, the value of Ep is E _p = 0.92, i.e. the decrease in the recorded pulse is 8% compared with distilled water. For N = 20, this decrease is 15% (E _p = 0.85). It should be noted that the decrease of E _p relative to unity is an indication of efficiency of the measurement system when implementing the method of multiple turnover probe pulse in the ring of the optical feedback. Indeed, for comparison we consider the magnitude of the laser probe pulse I (N) for Ν = I, i.e. the magnitude of the pulse recorded by the photodetector unit 4 and transmitted only once through the measuring cell 2 with a concentration of C = 0.5 mg / l, compared with the value of the same pulse transmitted once through the measuring cell at a concentration of C = 0, i.e. passed through distilled water (in reference cell 3). The value of E _p just gives the ratio of the values of such pulses: E _p = exp (-KLC) = exp (-0.00842) = 0.991 at C = 0.5 mg / L.

Thus, with a single pass through the measuring cell, a change in the value of the measured laser probe pulse, characterized by the value of E _p , makes it impossible to carry out an accurate measurement of such a small concentration value C = 0.5 mg / L. Indeed, in this case, when measuring the indicated low concentration of boric acid, the pulse value during measurement changes by less than one percent (E _p = 0.991), which significantly reduces the measurement accuracy when using the classical absorption measurement method using a single pass of the probe radiation through the measuring cell.

The proposed measurement system, which implements the method of multiple passage of radiation through the measuring cell, allows with sufficient accuracy to measure the concentration of boric acid C = 0.5 mg / l, as well as measure even lower concentrations, which is demonstrated in the simulation results of the measurement system presented in tab. 1. From this table it follows that in order to obtain accurate measurements of the concentration C = 0.1 mg / l, it is necessary to measure laser pulses with the number of passes N = 30 and N = 40. To implement measurements of such low concentrations, it is necessary to use a UV laser and an appropriate photodetector, the ratio of the radiation energy and the reception sensitivity of which is not less than the inverse of the parameter W shown in Table. 1. UV laser generators and photodetectors with such characteristics are manufactured by industry [11]. For example, when using a UV laser generator with an energy per pulse of the order of one millijoule and a UV detector with a standard sensitivity of about 100 photons per pulse, the potential level of the measurement system (potential B (16.1)) is B = 10 ¹³ , which exceeds the level potential attenuation W = 10 ^-11 for N = 30 in the table. 1 is 100 times the reciprocal of B. The allowable attenuation W for the indicated laser generator and photodetector is W = 1 / V = 10 ^-13 . To ensure measurements with the parameter N = 40, it is necessary to use a laser generator with an energy per pulse equal to 10 mJ (radiation power equal to 10 mW). It should be noted that the proposed measuring system allows the measurement of lower concentrations of boric acid C of the order of 0.05-0.01 mg / L. The parameter W in the table. 1 characterizes the requirements for the parameters of the laser generator and the photodetector unit and this parameter should be guided by the choice of elements, devices and laser generators used in the measurement system [11].

In FIG. 9 presents the results of modeling the operation of the measurement system in accordance with table. 1 when carrying out measurements of the concentration of boric acid C = 0.5 mg / l of a coolant substance. In FIG. 9 shows a sequence of pulses of probe laser radiation I (N) recorded by the photodetector unit 4 after each passage of the probe pulse along the optical feedback ring. In this case, the magnitude of the pulses of the probe LI gradually decreases with an increase in the number of revolutions N passed through the feedback ring. The number of revolutions (passes) along the feedback ring increases from one to N. At a number of revolutions N = 10, the value of the recorded pulse I (10) is 0.92 of the value of the pulse I (0) detected at zero concentration of boric acid (in the reference cell ) - a change of 8%. Thus, even at N = 10 revolutions of the probe pulse, accurate measurements of boric acid concentration of the order of C = 0.5 mg / L are possible. At N = 20, the indicated change (decrease) in the amplitude of the pulse is 0.85 of the pulse level at zero concentration of boric acid (decrease by 15%), which allows the measurement process to be performed with even higher accuracy. With a single passage of the probe pulse I (1) through the measuring cell, the decrease in amplitude relative to the zero pulse I (0) will be 0.992, i.e. less than one percent, which does not allow to ensure high measurement accuracy with only one passage of the probe pulse through the measuring cell, which is typical for the classical absorption method. Thus, shown in FIG. 9, the result shows a gradual increase in the sensitivity and accuracy of measurements with an increase in the number of passes N of the probe laser radiation along the optical feedback ring. Presented in FIG. 10 and FIG. 11 the results of modeling measurements of concentrations of boric acid 0.25 mg / l and 0.1 mg / l, showed a definite possibility of a fairly accurate determination of these small levels of concentrations. For example, when measuring a very low concentration C = 0.1 mg / L, the level of decrease in the amplitude of the probe pulse I (N), which must be recorded at N = 20 after twenty revolutions of the pulse along the feedback ring, is E _p = 0.967, t .e. 3.3% Modern digital measuring instruments reliably provide this measurement accuracy.

A number of additional factors should be noted for ensuring the operation of the measuring system when measuring low concentrations of boric acid. When measuring low concentrations, the photodetector unit 4 has to register a large range of laser pulse levels, which can exceed the allowable dynamic range for some types of photodetectors. To solve this problem, the proposed measurement system provides for the use of a controlled spectral filter 27, which performs two functions. The first function is associated with the implementation of narrow-band spectral filtering in the wavelength range generated by the first laser generator 1 and the second laser generator 8. Switching the filtered wavelengths is carried out promptly by control signals from the control unit 6. Unit 27 also performs the second function of dynamic protection of the photodetector unit 4 from pulses with a large amplitude arriving at the first moment of pulse generation from the laser generator 1, or 8. These pulses arrive after the first revolutions along the ring of samples tnoj connection, so suffered little attenuation and have a large amplitude. Block 27 performs the function of time gating and is opened for transmission only at the moment of receipt of the control pulse from the control unit 6. In this case, only the given pulse with a certain number of passed revolutions N, the arrival time of which is well known, is extracted and passes to the photodetector block. The amplitude of this pulse is controlled by the transmission of radiation in a controlled spectral filter 27. This solves the problem of suppressing previously arrived pulses having a large amplitude. Another solution to the problem of a large dynamic range is to reduce the energy of the emitted laser probe pulse by the laser generator 1 and 8. In this case, the generation level is selected (for example, using a LI 22 or 21 modulator) so that only the first pulses fall into the dynamic range of the photodetector unit 4 with a speed of N up to 10, and the remaining pulses with N more than 10 fall into the low sensitivity range of the photodetector and are not processed.

It should be noted that when equalizing the transmission of probe laser radiation when a measuring or reference cuvette is included in the optical feedback ring, there is no need to limit oneself to using only controlled attenuators 14 and 16. More accurate adjustment is performed at the second stage of the adjustment process, which is carried out digitally in the control unit 6 with high accuracy from the measured amplitudes of the laser probe pulses measured by the photodetector unit 4.

It should be noted that when switching from measurements of a low concentration of boric acid to measurements of a higher concentration, it is advisable to change the working wavelength generated by the first laser generator 1 and use longer wavelength ultraviolet laser radiation. This will allow you to more accurately match the characteristics of the photodetector unit 4 and the measurement system with the characteristics of the absorption of radiation in a coolant with a higher concentration of boric acid and will provide higher measurement accuracy. Currently, the industry has mastered laser generators with tuning the wavelength of the generated radiation. Similarly, when using a second laser generator 8 with a tunable wavelength of the generated radiation, a more accurate joint calibration of the measuring and reference cuvettes at several wavelengths of the control radiation is possible.

Based on the application materials, the process of propagation of the laser probe pulse along the optical feedback ring was simulated and the sensitivity of the method used to measure low concentrations of boric acid was increased. The results are shown in FIG. 9 - FIG. eleven.

The proposed measurement system uses blocks and units developed or manufactured by the industry. The measuring and reference cuvettes are made in the form of standard design developments using portholes that are transparent in a wide range from the short part of the UV range to the IR wavelength range. UV laser generators and photodetectors are manufactured by industry and are used in industry, medicine and scientific research. The optical instruments and elements that make up the proposed measuring system are designed and manufactured by the industry. Such elements include optical switches, fiber-optic lines with fiber adapters included in their composition for a range from 200 nm to the IR range, laser radiation modulators, controlled attenuators based on, for example, diaphragms mechanically controlled by step electric motors. The unit for measuring the parameters of laser radiation contains a diffraction grating and a line of photodetectors with sensitivity in the range from 0.2 to 0.8 μm. It is possible to use a standard industrial measuring device for measuring parameters of laser radiation in the range from UV to IR wavelengths. The photodetector unit 4 is made on the basis of a highly sensitive photoelectronic multiplier operating in the range of 200-800 nm. The signal processing unit 5 is based on standard circuits and elements in the first and second embodiment of the measurement system.

In the first embodiment of the construction of the measurement system in FIG. 1, the signal processing unit 5 contains an electronic pulse amplifier from the output of the photodetector unit 4, a digitizing unit and a computer interface unit included in the control unit 6. In the second embodiment of the construction of the measurement system in FIG. 2, the signal processing unit 5 contains standard electrical circuits used in the reception and registration of signals when performing heterodyne reception methods in the optical wavelength range. Block 6 contains in this case a resonant narrow-band amplifier of signals of intermediate frequency F _pr generated by the interaction (photoshooting) at the input of the photodetector block 4 of the received laser radiation from the output of the controlled spectral filter 27 and heterodyne laser radiation from the output of the first laser frequency shift block 52. Block 5 also contains a demodulator (detector), a digitizing block, and an interface unit with the control unit 6. Signal processing block 5 contains several of the indicated resonant amplifiers tuned to different intermediate frequencies for receiving laser radiation by the local oscillator method generated by the first laser generator 1 and separately by the second laser generator 8. The first and second options for constructing a measurement system contain a controlled spectral filter (USF) 27 that performs the function of a controlled narrow-band spectral filtering (U F) at the wavelengths of the first laser generator 1 and the second laser generator 8. At the same time, the USF 27 performs the function of gating the received pulsed laser radiation and transmits a laser pulse to the input of the photodetector unit 4 at a given time using control signals from the control unit 6. In USF 27 a predetermined attenuation of the transmitted laser radiation is also carried out by control from the control unit 6, i.e. USF 27 serves as a controlled filter-attenuator. The controlled spectral filter 27 operates on the basis of the acousto-optical effect of the interaction of laser radiation with an acoustic ultrasonic wave in a special crystal that is part of an acousto-optical cell. Thus, USF 27 consists of an acousto-optical cell of a special crystal and a piezoelectric element that excites ultrasonic waves in a given crystal, under the influence of which a dynamic phase structure is formed in the crystal, which changes the conditions for the propagation of laser radiation for a certain narrow spectral transmission band. As a result of this, a narrow band of a given wavelength of the first or second laser generators is filtered, the level is attenuated, and the laser radiation is time-gated. The generation of ultrasonic waves is carried out using a special electric generator, which is part of the controlled spectral filter 27, and generating a number of electrical frequencies according to the control signals from the control unit 6.

For operation in the UV range, for example, a quartz crystal transparent in the UV wavelength range is used. The controlled spectral filter 27 can be made on the basis of one acousto-optic cell (crystal) operating separately at both wavelengths of the first and second laser generators when various exciting electrical signals are applied to the cell. It is also possible to use two acousto-optic cells in the USF, each of which operates at the wavelength of one of the laser generators pos. 1 or 8. A block diagram of a controllable spectral filter 27 containing two acousto-optic cells is shown in FIG. 3, which shows two acousto-optical cells 56 and 57, two generators of electrical signals 58 and 59, two optical switches 60 and 61, which switch the optical input and optical output of the UVF to the operation of the acousto-optical cell 56 or acousto-optical cell 57 by control signals from block 6, to which these optical switches are connected, as well as electric signal generators 58 and 59. USF 27 contains reflective mirrors 62-65 and input and output diaphragms 68, 69, as well as piezoelectric elements 66 and 67. The operating principle is Mykh spectral filters based on the use of acousto-optic effect and acousto-optic cells is given in [8] and various publications [9-10]. Currently, the industry produces spectral tunable controlled filters, operating in the range from ultraviolet to infrared wavelengths. In the second version of the construction of the measurement system (Fig. 2), the frequency shift units of laser radiation 52 and 53 are contained, which, like the USF 27, are made on the basis of acousto-optic (AO) cells containing a crystalline cell and a piezoelectric element for excitation of ultrasonic waves in AO cells. leading to a frequency shift of the transmitted laser radiation by the frequency of the ultrasonic wave, which is determined by the frequency of the exciting electric signal from a special generator of electrical signals, which is part of the LN 52 and 53 of the frequency shift unit. In this case, the second shift unit 53 shifts the frequency of the transmitted laser radiation by a fixed value F. The acousto-optic cell included in the shift unit 53 operates in the Bragg diffraction mode, in which the cell exit in the corresponding direction laser radiation is generated with the optical frequency shifted by a predetermined amount and having a maximum intensity level of the converted radiation. The transmission coefficient of such converted radiation is close to 90-95%, which is especially important to reduce the loss of laser probe radiation during its propagation along the optical feedback ring. To operate at two wavelengths of laser radiation generated by laser generators 1 and 8, two separate acousto-optic cells are used as part of the frequency shift unit LI 53, which are switched on when the corresponding laser generators 1 or 8 are operating and operating at the corresponding wavelengths of the indicated laser generators. A block diagram of a second frequency shift unit LI 53 is shown in FIG. 4 and contains two acousto-optic cells 70 and 71, two generators of electrical signals 72 and 73. Two optical switches 74 and 75, which connect one of the acousto-optic cells 70 or 71 to effect a frequency shift of the laser radiation of the corresponding wavelength during operation of the first or second laser generators . The block diagram of FIG. 4 also contains reflective mirrors 76-79 and an input and output diaphragm 80, 81. The block diagram of FIG. 4 in general composition is similar to the block diagram of the implementation of the above USF 27 of FIG. Z. and corresponds to this pattern. This is due to the fact that in the USF 27 and in the frequency shift unit 53 the same effect of the interaction of laser radiation with ultrasonic waves in the crystal is used. However, used in USF 27 of FIG. 3 and in the frequency shift unit 53 of FIG. 4 acousto-optical cells operate in various modes and perform various functions. Therefore, there is no full correspondence or coincidence shown in FIG. 3 and FIG. 4 flowcharts. It should be noted that in the USF 27 and in the frequency shift unit 53 the same optical switches 60, 61 and 74, 75 are used, based on, for example, stepper motors. It should be noted that the second frequency shift unit LI 53 operates in a fixed frequency shift mode for transmitted laser radiation by F. This allows us to use the most efficient Bragg diffraction mode in acousto-optic cells included in this unit, in which more than 90% of the laser radiation receives the specified frequency shift and propagates in a fixed direction. The first frequency shift unit LI 52 generates a laser heterodyne signal (radiation) with a given optical frequency, which should change upon receipt and registration by the heterodyne optical method of probing laser radiation that has passed several revolutions along the optical feedback ring and received an additional shift of the laser radiation frequency, equal to NF. The block diagram of the first frequency shift unit LI 52 is shown in FIG. 5. The frequency shift unit 52 contains an acousto-optic cell 82 operating in a wide range of wavelengths of transmitted laser radiation and in a wide range of frequencies of the electrical signal supplied to the AO cell 82 from an electric signal generator 83 operating in a mode of generating control electric signals with different the frequency set from the control unit 6. The generator 83 contains an electric frequency synthesizer, which provides the formation of a control signal for the AO cell with a given frequency . The Bragg diffraction mode, as well as the Raman-Nath diffraction mode, is also possible here when the AO cell operates. The AO cell 82 operates at two LI wavelengths generated by the laser generators 1 and 8. In this case, when the frequency of the control signals from the generator 82 changes, a certain change in the direction of propagation of the laser radiation from the output of the AO cell 82 occurs. which propagates strictly along the optical axis of the system at any frequency of the control signal from the generator 83, are lenses 84, 86 and aperture 85. Lens 84 forms a defocused light beam in the plane of the diaphragm 85, which is located closer to the focal plane of the lens 84. Next, the diaphragm 85 extracts a part from the radiation beam that is localized on the optical axis of the system, and the lens 88 forms optical radiation propagating along the optical axis, which then goes to the optical output of the LI frequency shift unit — the output diaphragm 88. Thus, using an acousto-optical cell 82, a laser beam is formed with a given shift of the optical frequency and propagating along the optical axis of the system in a given direction. Further, this laser beam is directed to the input of the lens 7 of the photodetector unit 4 through mirrors 54 and 55 and is used as heterodyne radiation when receiving laser radiation that has passed N revolutions along the optical feedback ring. The principle of acousto-optic cells and their main parameters are given in the corresponding monographs and works [8-10].

Control unit pos. 6 in the proposed measurement system is based on a standard modern computer (personal computer (PC)), equipped with interfaces for communication with elements and units of the system, and for communication with a central computer for controlling the operation of a nuclear reactor. Thus, the construction of the proposed measurement system can be carried out on the basis of devices and elements of modern laser technology and electronics, mastered and manufactured by industry.

It should be noted that in the prototype and well-known analogs, it is known to use a radiation source and a photodetector unit, a signal processing and control unit, as well as a measuring and reference cell, sometimes called measuring and reference channels. Therefore, in the claims, the first laser generator, which performs the function of the main radiation source, is introduced in the restrictive part of the formula, together with a photodetector unit, a signal processing and control unit. A measuring and reference cuvette is also introduced in the restrictive part. Into the distinguishing part of the claims, fiber optic lines are introduced that perform the new function of optical delay lines in conjunction with the function of communication with a remotely located measuring cell.

Consider a number of modifications of the proposed measurement system.

The first modification concerns the implementation of the optical communication line between the measuring cell 2 and measuring equipment located in a separate room protected from radiation. In the first and second embodiments of the proposed system, this optical communication is carried out using fiber-optic lines 28 and 31, which simultaneously perform the function of optical delay lines of laser probe signals passing through the measuring cell 2. However, under the conditions of radiation, the parameters of the fiber-optic communication line may change (if you select the wrong material the fiber cable is made of). To prevent this phenomenon, two options are possible. First, fiber optic lines 28 and 31 can be placed in a protective lead sheath, which will prevent radiation from affecting the material of the fiber cable. Secondly, it is possible to abandon the use of fiber optic lines 28 and 31 and replace them with open (overhead) communication lines, as shown in FIG. 6. The optical connection between the measuring cell 2 and the measuring equipment in FIG. 6 is carried out using open optical lines formed by reflective mirrors pos. 89-91 (input line) and pos. 92-94 (output line). The optical lines are housed in protective housings 95 and 96. Optical guide elements — lenses, which are shown in FIG. 6 are not shown. However, due to the high directivity of laser radiation (low divergence), the use of additional guide elements in the form of lenses is not required. In this case, the introduced open optical lines continue to fulfill the second function of the optical delay lines of the laser probe signals. Fiber optic lines 34 and 37 for the reference cell 3 can be left or also replaced with open optical communication lines. The optical transmission equalization of the optical communication lines for the measuring and reference cuvettes is still carried out using the first and second controlled attenuators 14 and 16.

It should be noted separately the use of these open optical communication lines when used in the proposed measurement system of the laser generators of the UV range, operating in the short part of the UV wavelength range. Currently, laser generators have been developed that generate laser radiation shorter than 200 nm, for example, a UV laser with an operating wavelength of 110 nm. The use of such laser generators is very effective, since with a decrease in the wavelength in the UV range, the absorption of boric acid and the corresponding extinction coefficient increase significantly. However, this laser radiation has a noticeable absorption during propagation in the air. To reduce losses during the transportation of this laser radiation, the optical communication lines in FIG. 6 should be placed in a vacuum environment, for which air from the housings 95 and 96 is evacuated, or a reduced atmospheric pressure is created inside these housings. This will make it possible to use in the proposed measurement system a more efficient probe laser radiation of a short part of the UV wavelength range and to ensure the measurement of low concentrations of boric acid in the composition of the coolant of a nuclear reactor.

Let us now consider the second version of the modification of the proposed measurement system, associated with the use of several measuring cuvettes installed in several places (points) of the primary coolant circuit of a nuclear reactor. The block diagram of FIG. 8 represents such a modification of the proposed measuring system, which contains three measuring cuvettes. This block diagram shows two additional measuring cells pos. 97 and 98, newly introduced in addition to the main measuring cell pos. 2. The indicated three measuring cuvettes by means of additional linear optical switches pos. 99-104 and previous optical switches pos. 12 and 23 are individually included in the optical measurement system. In this case, the new measuring cuvettes 97 and 98 are connected by means of additional bypasses at separate additional control points of the primary coolant circuit of the nuclear reactor. This allows you to obtain operational information about the parameters of the coolant in various zones and parts of the circuit and increase the efficiency of controlling the operation of a nuclear reactor. In general, the operation of a measuring system with three measuring cuvettes is no different from the operation of a measuring system with one measuring cuvette. By commands from the control unit 6 individually, any one measuring cuvette is connected to the measuring circuit by means of new linear optical switches and optical switches 12 and 23, then the measurement process described above is carried out. In FIG. 8, pipelines for connecting measuring cuvettes at various points of the primary coolant circuit are not shown.

Based on the materials of this application for the invention, a prototype of a measurement system was developed and investigated, measurements of the parameters of the studied materials and solutions of substances in distilled water were carried out, parameters of a boric acid solution of a given concentration were determined, and extinction coefficients of boric acid were measured for various wavelengths of the ultraviolet wavelength range, as well as parameters of boric acid in the blue-green region of the visible spectrum. The results obtained indicate the possibility and prospects of measuring the concentration of boric acid by the proposed method using the presented measurement system in the ultraviolet wavelength range and using the blue-green part of the visible range as control laser radiation. The proposed measurement system provides the measurement of large concentrations of boric acid of the order of tens of grams per liter of coolant. At the same time, the proposed measurement system provides measurements of small concentrations of boric acid up to values of 0.5-0.1 mg / l of coolant. This high sensitivity when measuring low concentrations of the investigated substances is achieved by repeatedly passing the probe laser radiation through the measuring cuvette by organizing optical feedback, which includes a measuring cuvette with the test substance. As a result of this, the sensitivity of the absorption-spectral measurement method used increases by a factor of N, where N is the number of revolutions of the probe laser radiation along the optical feedback ring, including the measuring cell. In addition, an increase in the sensitivity and reliability of measurements is ensured by the use of a reference cell, in which any precisely defined concentration of boric acid solution in distilled water is established. In this case, the reference cell has optical parameters identical to the measuring cell. In the measuring system, a periodic connection to the measurement scheme of the reference or measuring cell using optical switches is provided. Next, a comparison is made of the parameters of the pulses of the probe laser radiation transmitted through the measuring and reference cells during the same number of revolutions N along the optical feedback circuit, which can significantly increase the accuracy and reliability of measurements and provide continuous monitoring of the parameters of the coolant in the primary circuit of a nuclear reactor. An important advantage of the proposed measurement system is the ability to connect to the measuring circuit and take measurements on several measuring cuvettes connected in various places of the primary coolant of the nuclear reactor. This allows you to quickly monitor the parameters of the coolant at various points in the circuit, which is important for effective and safe control of the operation of a nuclear reactor. The proposed measurement system has high speed and efficiency in carrying out measurements. Actually, the time of measuring the concentration of boric acid in the coolant passing through the measuring cell is several milliseconds and is determined by the processing time of the information in the control unit 6 (in the PC) obtained by registering one probe laser pulse. An important factor in increasing the accuracy of measurements, the reliability and confidence of the information received is the ability to fill the reference cell with a solution of boric acid of any given concentration, performed by the operator, subsequent measurements using this reference cell and measuring cell, processing and comparing the results. It should be noted that it is possible to check (test) the optical parameters of the measuring cell using a second laser generator and compare these parameters with the parameters of the reference cell without disconnecting the measuring cell from the primary coolant circuit in the operating mode of a nuclear reactor.

In the submitted application for the invention, two factors of novelty should be noted. Firstly, it should be noted as a novelty of the invention the implementation in the measuring system of a new embodiment of the absorption-spectral method of measurements based on the multiple passage of the probe laser radiation through the measuring cell, implemented by introducing an optical feedback ring, including both the measuring cell and the reference cell , which is filled with a solution of boric acid with a given concentration and precisely known optical parameters. In this case, to separate the laser beams that have passed a different number of revolutions along the optical feedback ring, we use the time separation of the laser pulses using the optical delay line in the first embodiment of the measurement system, or use the frequency coding of the laser radiation by adding a fixed shift of the optical frequency for each separate passage of the probe radiation along the optical feedback ring in the second embodiment of the construction of the measuring system . This new measurement method allows increasing the sensitivity of the classical absorption spectral measurement method by a factor equal to the number of revolutions of the probe laser radiation passing through the optical feedback ring N, which is especially important when measuring low concentrations of boric acid or other substances with a low extinction coefficient.

Secondly, it should be noted as a novelty of the invention the implementation of measuring the concentration of boric acid directly in the primary circuit of the coolant of a nuclear power reactor by the indicated new version of the absorption spectral optical method, ensuring high accuracy, reliability and efficiency of measurements while solving a number of problems that arise when applying modern technical means in nuclear power. It should be noted that the use of the proposed measurement system as part of a nuclear power reactor allows you to realize the following advantages and provide a solution to the following problems in the operation of modern nuclear reactors:

1) Ensuring the possibility of monitoring the composition of the coolant directly in the circuit under the current parameters of the aquatic environment. In this case, it is possible to determine the concentration of not only boric acid, but also other possible impurities formed during prolonged operation of a nuclear reactor and exposure to radiation. To detect these impurities, it is possible to use the entire spectrum of laser radiation from short ultraviolet to infrared radiation that can propagate in an aqueous medium.

2) In unattended and semi-serviced rooms of the first circuit (strict mode zone), only measuring cuvettes are installed. Auxiliary equipment of the measuring system and information display devices can be taken out to any room of the NPP. Such a structure, with a high service life of the measuring cuvettes, will reduce the dose loads of the NPP staff.

3) The application of the proposed measurement system eliminates the need for sampling the coolant from the primary circuit. This ensures a reduction in the dose loads of NPP personnel and eliminates the discharge of radioactive media obtained during sampling from the primary circuit. Thus, the operating mode of the corresponding special NPP units is softened.

4) Removing a person from the measurement process (which is typical for chemoluminescent measurement methods with sampling) eliminates the subjective random measurement error. The metrological characteristics of measurements are significantly improved due to the absence of transport delay of the sample in long pulse lines, the measurement efficiency is increased, which is of great importance for the control system of a nuclear reactor and increase the safety of nuclear power plants.

Due to the high accuracy of measurements, a wide range of measurements of the concentrations of the investigated substances and the high efficiency of measurements, the proposed measuring system will find application in various fields of production, the chemical, oil refining industries and environmental monitoring and environmental control systems.

Information sources

1. Sarylov V.I. The use of the chemoluminescent method for monitoring the parameters of the reactor water of nuclear power plants. Chemistry and water technology, 1982, v. 4, No. 1, p. 45-47.

2. Bovin V.P. Neutron-absorption analyzer of Boron in the primary coolant of the WWER. Atomic Energy, 1976, v. 38, no. 5, p. 283-286.

3. RF patent No. 2025800 dated 12/30/1994. The method of controlling the content of Boron-10 in the coolant of the primary circuit of a nuclear reactor.

4. England patent No. 1157086. Two-beam photometer.

5. RF patent No. 2022239 from 10.30.1994. Device for optical absorption analysis.

6. RF patent No. 750287 of 07.23.1980. Device for optical absorption analysis. Double beam photometer (prototype).

7. Mankevich S.K., Nosach O.Yu., Orlov E.P. RF patent No. 2152056 from 06/27/2000. The method of laser location and device for its implementation.

8. Balakshiy V.I., Parygin V.N., Chirkov L.E. Physical foundations of acousto-optics. M .: Radio and communication, 1985, p. 134-234.

9. Balakshiy V.I., Mankevich S.K., Parygin V.N. Quantum Electronics. 1985, vol. 12, No. 4.

10. Mustel E.R., Parygin V.N. Methods of modulation and scanning of light. M .: Nauka, 1970.

11. Handbook of laser technology // Edited by Napartovich A.P. M .: Energoatomizdat, 1991.

12. Physico-chemical methods for investigating in-loop chemical processes in atomic energy systems. Tsniatominform, 1986.

13. Eristova D.I., Brouchek F.I. Analytical methods for determining boron. Tbilisi, 1965.

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Claims (17)

1. A system for measuring the concentration of boric acid in the primary circuit of a coolant of a nuclear power reactor, comprising a first laser generator, a measuring and reference cell, electrically coupled photodetector unit, a signal processing unit and a control unit, wherein the photodetector unit is equipped with a lens, and the control input of the first laser generator connected to a control unit, characterized in that the second laser generator, the first and second laser radiation modulators, the first, second and third optical switches, four fiber-optic lines, three controlled optical attenuators, a controlled spectral filter, a unit for measuring laser radiation parameters, five reflective mirrors and five translucent mirrors, while the optical outputs of the first and second laser generators are connected to the optical inputs of the first and second, respectively modulators of laser radiation, the optical output of the first laser modulator is connected to the optical input of the first optical switch by sequentially mounted on the optical axis of the first, second and third translucent mirrors, the optical output of the first laser modulator is additionally connected to the optical input of the third controlled attenuator by the first and second translucent mirrors, the optical output of the second laser modulator is connected to the optical input of the first optical switch by the fourth reflective mirror of the first, second and third translucent mirrors, the optical output of the second laser modulator is radiated additionally optically connected to the optical input of the third controlled attenuator by means of a fourth reflective mirror, first and second translucent mirrors, the first optical output of the first optical switch is optically connected to the input of the first fiber optic line through the first optical attenuator, the optical output of the first fiber optic line is connected to optical input of the measuring cell, the second optical output of the first optical switch is optically connected to the input of the third fiber optical line through a second controlled attenuator, the optical output of the third fiber optic line is connected to the optical input of the reference cuvette, the optical output of the measuring cell is connected to the input of the second fiber-optical line, the optical output of which is connected to the first optical input of the third optical switch, the optical output of the reference the cuvette is connected to the optical input of the fourth optical fiber line, the output of which is connected to the second optical input of the third optical switch, the optical output One of the third optical switch is optically connected to the optical input of the first optical switch by means of sequentially mounted and optically connected third reflective mirrors, the fifth translucent mirror, the second reflective mirror and the third translucent mirror, the optical output of the third optical switch is additionally connected to the first optical input of the second optical switch by the third reflective mirror and fifth translucent mirror, optical in the output of the third controlled attenuator is connected to the second optical input of the second optical switch by means of the fourth translucent mirror, the first and fifth reflective mirrors, the optical output of the third controlled attenuator is additionally connected to the optical input of the laser radiation measurement unit by the fourth translucent mirror, the optical output of the second optical switch is connected to optical input of a controlled spectral filter, the optical output of which is connected with cally photodetector entrance lens unit, second control input of the laser generator and the control inputs of the first and second laser light modulators connected to the control unit, control inputs of the three optical switches and three controllable attenuators are connected to the control unit, the control input managed spectral filter is connected to the control unit. 2. The measurement system according to claim 1, characterized in that it uses a laser generator of the ultraviolet wavelength range as the first laser generator. 3. The measurement system according to claim 1, characterized in that the first and second laser generators are configured to tune the wavelength of the generated laser radiation. 4. The measurement system according to claim 1, characterized in that in it the optical switches contain a reflective mirror and a stepper motor. 5. The measurement system according to claim 1, characterized in that the controllable spectral filter is based on an acousto-optic cell operating in the ultraviolet wavelength range and in the short-wavelength part of the visible wavelength range. 6. The measurement system according to claim 1, characterized in that the controlled spectral filter contains two acousto-optical cells and two optical switches, including acousto-optical cells in turn in the optical circuit of the measurement system. 7. The measurement system according to claim 1, characterized in that the reference cuvette is equipped with a working substance filling unit, equipped with inlet and outlet taps. 8. A system for measuring the concentration of boric acid in the primary circuit of a coolant in a nuclear power reactor, comprising a first laser generator, a measuring and reference cuvette, electrically coupled photodetector unit, a signal processing unit and a control unit, wherein the photodetector unit is equipped with a lens, and the control input of the first laser generator connected to a control unit, characterized in that the second laser generator, the first and second laser frequency shift blocks, the first, second and third optics are introduced optical switches, four fiber optic lines, three controlled optical attenuators, a controlled spectral filter, a unit for measuring laser radiation parameters, five reflective mirrors and seven translucent mirrors, while the optical output of the first laser generator is connected to the optical input of the first optical switch by means of optical axis of the first, second and third translucent mirrors, the optical output of the first laser generator is additionally associated with optical the input of the third controlled attenuator by means of the first and second translucent mirrors, the optical output of the second laser generator is connected to the optical input of the first optical switch by the fourth reflective mirror, the first, second and third translucent mirrors, the optical output of the second laser is additionally optically connected to the optical input of the third controlled attenuator by means of a fourth reflective mirror, first and second translucent mirrors, first op The optical output of the first optical switch is optically connected to the input of the first fiber optic line through the first optical attenuator, the optical output of the first fiber optic line is connected to the optical input of the measuring cell, the second optical output of the first optical switch is optically connected to the input of the third fiber optic line through the second controlled attenuator, optical output of the third fiber optic line is connected to the optical input of the reference cell, optical output of the measuring cell AET is connected to the input of the second fiber-optic line, the optical output of which is connected to the first optical input of the third optical switch, the optical output of the reference cell is connected to the optical input of the fourth fiber-optic line, the output of which is connected to the second optical input of the third optical switch, the optical output of the third the optical switch is optically coupled to the optical input of the second laser frequency shift unit via a third reflective mirror, the fifth half of the secondary mirror and the second reflective mirror, the optical output of the second laser frequency shift unit is optically coupled to the optical input of the first optical switch via a third translucent mirror, the optical output of the third optical switch is additionally connected to the first optical input of the second optical switch through the third reflective mirror and the fifth translucent mirror , the optical output of the third controlled attenuator is connected to the second optical input of the optical switch by means of the fourth translucent mirror, the first reflective mirror and the sixth translucent mirror, the optical output of the third controlled attenuator is additionally connected to the optical input of the laser radiation measurement unit by the fourth translucent mirror, the optical output of the third controlled attenuator is optically connected to the optical input of the first frequency shift unit laser radiation through a fourth translucent mirror, the first neg of the secondary mirror and the sixth translucent mirror, the optical output of the first block of the frequency shift of the laser radiation is optically connected to the optical input of the lens of the photodetector unit via the sixth reflective mirror and the seventh translucent mirror, the optical output of the second optical switch is connected to the optical input of a controlled spectral filter, the optical output of which is connected to optical input of the lens of the photodetector block through the seventh translucent mirror, the control inputs of the second laz The first generator, the first and second laser frequency shift blocks are connected to the control unit, the control inputs of three optical switches and three controlled attenuators are connected to the control unit, and the control input of the controlled spectral filter is connected to the control unit. 9. The measurement system of claim 8, characterized in that it uses a laser generator of the ultraviolet wavelength range as the first laser generator. 10. The measurement system of claim 8, wherein the first and second laser generators are configured to tune the wavelength of the generated laser radiation. 11. The measurement system of claim 8, characterized in that the optical switches comprise a reflective mirror and a stepper motor. 12. The measurement system of claim 8, wherein the controllable spectral filter is based on an acousto-optic cell operating in the ultraviolet wavelength range and in the short-wavelength part of the visible wavelength range. 13. The measurement system of claim 8, wherein the controllable spectral filter contains two acousto-optic cells and two optical switches, including acousto-optic cells alternately in the optical circuit of the measurement system. 14. The measurement system of claim 8, wherein the first laser frequency shift unit comprises optically coupled input diaphragm, an acousto-optic cell with a control unit, a first lens, a pinhole, a second lens and an output diaphragm, sequentially mounted on the optical axis wherein the control electrode of the acousto-optic cell is connected to the control unit of the acousto-optic cell. 15. The measurement system of claim 8, characterized in that the second laser frequency shift unit in it comprises two acousto-optic cells and two optical switches, including acousto-optic cells alternately in the optical circuit of the measurement system. 16. The measurement system of claim 8, characterized in that the reference cuvette is equipped with a working substance filling unit, equipped with inlet and outlet taps. 17. The measurement system of claim 8, characterized in that it contains three measuring cuvettes, optically coupled through fiber optic lines with optical inputs of six additional optical switches, alternately optically including the measuring cuvettes in the optical circuit of the measuring system, and the measuring cuvettes are connected to the first coolant circuit of a nuclear power reactor at its various points.

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