JP2882807B2 - Automatic boron concentration analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an automatic boron concentration analyzer for automatically analyzing and measuring boron concentration (boron concentration) used for reactivity control of a PWR plant.

[Prior Art] FIG. 5 shows the structure and principle of a conventional device. In FIG. 5, the boron detector of the neutron absorption system detects a neutron source 11, a moderator (high-density polyethylene, etc.) 12 for decelerating high-speed and medium-speed neutrons generated by statistical establishment from the source to a thermal neutron, and a thermal neutron. A neutron flux detector 10 composed of a neutron detector 13 that detects well, and a circuit that performs arithmetic processing on a neutron detection signal
20 and a display unit 30 for displaying the result. The process fluid to be measured is inserted between the neutron source 11 and the neutron flux detector 13, but the number of neutrons that can reach the neutron flux detector 13 depends on the boron concentration of boron because boron has a large thermal neutron absorption cross section. Therefore, the boron concentration can be measured by using this relationship. Strictly speaking, the inner natural isotope boron so that B ¹⁰ present in a ratio of 19.80% is that measuring the concentration of so B ¹⁰ absorption cross section of neutron is large.
Further, since the thermal neutron absorption cross section of boron is inversely proportional to the energy temperature of neutrons, a temperature drift occurs, so a temperature correction circuit is incorporated.

The boron concentration of the primary coolant of PWR is in a wide range from 0 ppm to 5000 ppm.

The concentration of boron is the main means of controlling the reactivity of PWR, so that it can be measured with high accuracy / response over a wide range as an automatic analysis and measurement device. One of the purposes of the automatic analysis and measurement device is to save labor. For this reason, it is necessary that the frequency of calibration be low and stable measurement can be performed without human intervention for a long time.

On the other hand, manual analysis, which is currently used for official data, requires a specialized operation analyst, but can be measured with an accuracy of about ± 5 ppm in about 15 minutes. There has been no boron concentration automatic analyzer with such accuracy
The boron concentration of PWR primary coolant was measured and controlled by manual analysis.

Since the boron concentration is the main means of controlling the reactivity of the PWR, the burden on the analyst for manual analysis is large, and in the load adjustment operation of the PWR that will be put into practical use in the future, the boron concentration changes greatly in a short period of time. Performing the measurement by hand analysis increases the burden on the analyst, and is not desirable for the automatic control of the boron concentration. The emergence of a highly accurate automatic analyzer of the boron concentration is strongly demanded.

[Problems to be solved by the invention]

There are the following problems to realize a boron concentration automatic analyzer that can measure boron concentration with high accuracy and responsiveness in place of manual analysis and that can measure stably for a long period with less calibration frequency for labor saving. .

(1) The factors and the degree of the errors are unknown, and it is necessary to quantitatively grasp them.

(2) Neutron emissions from neutron sources are statistical and have statistical errors. Am-Be as a conventional neutron source (americium - beryllium), the count rate in this combination is used _of BF ₃ counter as a neutron flux detector 10 ³ cps (coun
In order to reduce the statistical error by increasing the number of counts, it takes a long time, the response is poor, and the state must be kept constant during that time.

(3) the count rate and the boron concentration (strictly B ¹⁰ concentration)
Is nonlinear, but this is approximated by a quadratic function. Since the measurement range is as wide as 0 to 5000 ppm, the error of this function approximation is large.

(4) Since the neutron absorption cross section of boron is a function of neutron energy (temperature), it is affected by temperature fluctuation. For this reason, although a temperature compensating circuit is provided, the thermal conductivity of the moderator is very poor, and the thermal non-equilibrium state of each part is long when the temperature fluctuates, so that the temperature compensation is difficult and cannot be completely compensated.

(5) The voltage applied to the neutron flux detector changes due to not only the process temperature but also the ambient temperature of the arithmetic processing unit, and the count rate changes. There is a discriminating circuit that extracts only neutron pulses from the pulse shape of the neutron detector count output signal in order to eliminate the effects of gamma rays, etc., but this threshold also drifts due to temperature fluctuations, and this also causes temperature fluctuation errors. Becomes

(6) PWR B ¹⁰ concentration of the in the primary coolant existence ratio from 19.80% of the original will be impaired as proceeds operated by neutron absorption in the fuel fission decreases.

Therefore although it if no problem is to measure the B ¹⁰ concentration becomes an error factor when measuring the boron concentration.

 The above is summarized in FIG.

[Means for solving the problem]

The automatic boron concentration analyzer according to the present invention is a neutron detector
In the boron concentration analyzer including the 110, the arithmetic processing circuit unit 120, and the display unit 130, the neutron detection unit 110 includes a neutron source 1
11, moderator 112, neutron detector 113, and sampler tank 11
4, a neutron source 111 using either Am-Be or Cf, a neutron detector 113 using a He ³ counter, and a temperature controller and a flow controller upstream of the neutron detector 113. The relationship between the count rate of the neutron detector 113 and the boron concentration is divided into a plurality of small regions in the range of the boron concentration of 0 to 5000 ppm, and a quadratic curve is approximated in the region. A computer including a number counter 122, a computer 123, and a correction processing unit 124;
123 inputs the outputs of the output and B ¹⁰ abundance setter 125 of the pulse number counter 122, the temperature signal third temperature signal 2 and the arithmetic processing circuit unit 120 of the temperature signal 1 and the neutron detector 113 neutron source 111 Is input and output to the display unit 130.

[Action]

Neutrons are generated using either Am-Be or Cf as a neutron source, and counted by a neutron detector (He ³ counter) having a higher neutron absorption rate.

Providing a temperature controller and a flow controller upstream of the neutron detector prevents process temperature and flow fluctuations.

The function formula of the neutron detector count rate and the boron concentration increases the accuracy of the function fitting by dividing the range of the boron concentration from 0 to 5000 ppm into a plurality of small regions and approximating the region with a quadratic curve.

The correction processing unit corrects the effects of the temperature of the neutron source, the temperature of the neutron detector, and the temperature of the arithmetic processing unit.

〔Example〕

First, error factors (FIG. 6) and points for solving the problems will be described.

(1) The factors of error are extracted by physical considerations and experiments, and the degree to which each factor affects the error is identified, and items for solving the problem are narrowed down. This provides a starting point for deriving the following (2) to (6).

(2) Optimizing the arrangement of neutron sources and detectors to increase the count rate at the neutron detector to reduce statistical errors and improve responsiveness. Also, a neutron source with a high neutron generation rate and a neutron detector with a higher neutron absorption rate are used.

(3) In order to more accurately perform the function fitting of the neutron detector count rate and boron concentration, the range of boron concentration of 0 to 5000 ppm is divided into a plurality of regions, and a quadratic curve approximation is performed in a small range. The region may be further divided into smaller approximations and a first-order approximation may be used, or conversely, the region mesh may be roughened and used as a third-order or higher polynomial approximation.

(4) Since a process temperature fluctuation cannot be completely corrected, a constant temperature control device is provided upstream of the boron concentration meter. In addition, a constant flow rate control device is installed to suppress the flow rate fluctuation that causes the process temperature fluctuation. Further, the temperature correction processing unit 124 is also used to correct the influence of the fluctuation of the ambient temperature (due to season, day and night, etc.) and the fluctuation of the process temperature. The temperature detector for temperature correction can be used in the process fluid section in addition to the conventional moderator section.

(5) An arithmetic processing unit temperature correction processing unit 124 is provided to correct the influence of the temperature drift of the arithmetic processing unit.

(6) Since the loss of B ¹⁰ is caused to gradually, provided the correction processing unit 124 that can be input separately obtained B ¹⁰ abundance corrected by this value.

Next, an embodiment of the present invention is shown in FIGS. FIG. 1 shows the configuration of an embodiment of the present invention. The neutron source 111 americium - using beryllium (Am-Be) or Californium ⁽²⁵² Cf).

a = distance from the neutron source to the sampler tank b = distance from the sampler tank to the neutron detector When a and b are determined by calculation analysis or experiment so that the optimal arrangement is obtained, that is, the count rate is maximized. Set.

As the moderator 112, polyethylene is used. The neutron detector 113 uses a He ³ counter.

In order to perform more accurate function fitting under the neutron detector count rate C and boron concentration, the range of boron concentration 0
50005000 ppm Divided into a plurality of small areas, and a quadratic curve is approximated in the small range. A temperature constant controller 118 and a flow rate constant controller (not shown) are provided upstream of the neutron detector to prevent process temperature fluctuation.

The circuit unit 120 for processing the neutron detection signal is an amplifier 121
And a pulse number counter 122 and a computer 123.

The B ¹⁰ abundance setter 125 inputs to the computer 123 sets the presence ratio of B ^10, providing the correction processing unit 124 can be corrected by that value. The correction for correcting the influence of the temperature drift of the arithmetic processing unit is also performed by the correction unit 124.

FIG. 2 shows a plateau curve of the embodiment of the present invention. The plateau region has several hundred volts and the applied voltage is usually set in this range to eliminate the effects of voltage fluctuations. However, it is required to maintain the applied voltage stably with a slope of about 1% / 100V with the best characteristics. Is done.

FIG. 3 shows a pulse height distribution curve of the embodiment of the present invention.

The pulse height distribution density differs depending on the type and shape of the detector. The longer the length L in FIG. 3 and the smaller the ratio of the surface types of the inclined portions, the higher the accuracy of noise discrimination and the less affected by pulse width variations due to temperature variations and the like.

FIG. 4 is a diagram showing an error in case of obtaining the relationship between the detector count rate C and boron concentration C _B experimentally.

When approximating with a quadratic curve over a wide range, the error becomes large. Therefore, quadratic approximation is performed by dividing into small ranges.

According to the above embodiment, the error factors shown in FIG. 6 are dealt with as follows.

(1) The statistical error associated with neutron emission is (F: count rate, t: measurement time) and can be reduced by increasing F or increasing t. It can be dealt with by increasing t, but in this case, since the response time becomes long, the method of increasing F is adopted and the following measures are taken.

(A) As a measure to increase the neutron counting rate For the arrangement of the neutron source and counter, the optimum arrangement will be determined based on the test results.

The neutron source can be changed to the intensity type ( ²⁵² Cf).

Change BF ₃ to He ³ to increase the efficiency of the counter. He
³ has a larger neutron absorption cross-section than B ^{10 and} He ³ has no toxicity and can be pressurized, so the counting rate increases 3 to 10 times.
The error is less than ~ 2 ppm.

(B) Also note the following.

The counting rate is determined by matching with the downstream Amp circuit. 10 ⁴ to 10 ⁵ cps is the current limit. It is also desirable that the pulse width is small and the pile-up effect is small. This is because the pile-up effect is large, and if the pulse width is large, each pulse overlaps with an increase in the count rate, which causes counting down.

The plateau curve is flattened. In addition, the discrimination setting should be easier than the pulse height distribution curve (Figs. 2 and 3).

The neutron flux range of the detector is determined so that the neutron flux level at the detector location can be measured. This is because the neutron flux level differs depending on the neutron source.

Through calculations and experiments to satisfy the above
Optimum He ³ filling pressure and detector size. When the neutron source is 1 ci (Curie), the He ³ detector is 5 to 10 kg / cm ²
The optimal pressure is about 1 ^B in outer diameter and about 10 ^{B in} effective length. (1B is 1 inch long.) (2) Fitting error After selecting the neutron source and detector type and arrangement according to the above item (1), the relationship between the detector count rate and the boron concentration is experimentally obtained. . This relational expression is close to a quadratic curve, but if it is approximated by a quadratic curve over a wide range, an error occurs as shown in FIGS. 4 (a) and 4 (b).

Therefore, the processing of item (3) for solving the problem is performed. Thereby, the fitting error can be greatly reduced as shown in FIG. 4 (c).

(3) Temperature fluctuation error The amount of change in the relational expression between the detector count rate and the boron concentration due to the process temperature fluctuation and the ambient temperature fluctuation is obtained by experiments. At this time, the temperature of each part of the automatic boron concentration analyzer is measured at the same time, and a relational expression between the temperature of each part and the amount of change is obtained, and a temperature correction process is performed using this relational expression.

However, since it is most effective not to cause temperature fluctuation, a temperature constant controller is provided. The temperature control operating end raises the temperature of the cooling water by the heater from the responsiveness and maintains the temperature at a constant value equal to or higher than the ambient temperature.

〔The invention's effect〕

Since the present invention is configured as described above, the present invention has the following effects.

(1) Statistical errors can be reduced by providing a controller for keeping the temperature and flow rate of the fluid constant, and by employing means for increasing the number of counts.

(2) By approximating the relationship between the count number and the boron concentration in small regions, it is possible to measure with high accuracy over a wide range.

(3) Operation to be correct for the effects of loss of B ¹⁰ component of the accompanying natural boron, also a neutron neutron detector from the detector (neutron source neutron absorbing system having a drift compensation function due to temperature variation (A neutron source and neutron detector based on the principle that the number of particles arriving at the reactor decreases as the boron concentration increases during the process).

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention, FIG. 2 is a diagram showing a plateau curve of the embodiment of the present invention, FIG. 3 is a diagram showing a pulse height distribution curve of the embodiment of the present invention, FIG. 4 is a diagram showing an error when the relationship between the detector count rate and the boron concentration is experimentally obtained, FIG. 5 is a diagram showing a configuration of a conventional device, and FIG. 6 is a diagram showing an error factor of the conventional device. is there. 10,110: Neutron detector, 11,111: Neutron source, 12,112
... Moderator, 13,113 ... Neutron detector, 14,114 ... Sampler tank, 15,115 ... Piping (inflow example), 16,116 ...
Piping (example of outflow), 17,117: Wiring, 118: Heater, 119
...... controllers, 20, 120 ...... arithmetic processing circuit unit, 21, 121 ...... amplifiers, 22, 122 ...... pulse number counter, 23, 123 ...... .mu. computer, 124 ...... correction processing unit, 125 ...... B ¹⁰ abundance setter, 30,130 ... Display unit (indicator or computer).

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-49-18095 (JP, A) JP-B-45-4234 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01T 1/00-7/12 G21C 17/00-17/14

Claims (1)

(57) [Claims] A neutron detector (110) and an arithmetic processing circuit (1)
(A) The neutron detector (110) includes a neutron source (111), a moderator (112), a neutron detector (113), and a sampler tank (130). (B) a neutron source (111) using either Am-Be or Cf, (C) a neutron detector (113) using a He ³ counter, and (D) a neutron. A temperature controller and a flow rate controller are provided upstream of the detector (113). (E) The relationship between the count rate of the neutron detector (113) and the boron concentration is as follows. (F) The arithmetic processing circuit section (120) includes an amplifier (121), a pulse counter (122), a computer (123), and a correction processing section (124). (G) The computer (123) is provided with a pulse number counter (1).
Inputs the output of the output and B ¹⁰ abundance setter 22) (125), the temperature signal (2) and the arithmetic processing circuit unit of the temperature signal (1) and the neutron detector of the neutron source (111) (113) An automatic boron concentration analyzer characterized in that the temperature signal (3) of (120) is input and output to a display unit (130).