RU2743234C9 - Method for monitoring neutron flux density - Google Patents

Abstract

FIELD: nuclear industry.

SUBSTANCE: invention relates to a method for monitoring density of the neutron flux, and can be used in control systems, monitoring and protection of nuclear installations. Ionization pulse-current fission chamber registers a neutron flux, discriminates pulse signal in amplitude, and forms formalized pulses. Then formalized pulses are converted into a code proportional to the number of pulses from the discriminator, and that number is corrected according to the algorithm for calculating count rate of pulse signal of the fission chamber according to the corrective characteristic of pulses miscalculations, after which a signal is generated proportional to count rate of pulse signal of the fission chamber. Corrective characteristic is dependence of count rate of pulse signal from the fission chamber on the number of pulses from the discriminator at different values ​​of the measuring channel load.

EFFECT: improved accuracy of monitoring neutron flux density in a wide range of measurements.

1 cl, 2 dwg

Description

The invention relates to the field of reactor measurements and can be used in control systems, monitoring and protection of nuclear installations.

The known method [RF patent No. 2193245, publ. 20.11.2002], including registration of neutrons by an ionization pulse-current fission chamber, single-level discrimination of the signal by amplitude, formation of formalized pulses, conversion of pulses into a code proportional to the number of pulses N _D from the discriminator, formation of a signal in a PC proportional to the count rate of a pulse signal N _OUT fission chambers.

The disadvantage of this method is the low accuracy of measuring the count rate in the mode of transition from the pulsed measurement mode to the current one (it is believed that in the pulsed mode the count rate, and the current in the current mode are proportional to the neutron flux density at the point of the detector location), which is due to the high percentage of superimposed pulses with increasing loading channel N_BX above 10^five imp / s. The resulting signal from the superimposed pulses with a further increase in the amplitude of the load exceeds the value of the discrimination threshold, which leads to the occurrence of miscalculations of the pulses.

The closest in technical essence of the known technical solutions is implemented by means of the device described in the patent of the Russian Federation No. 2240609 [publ. 20.11.2004], a method for measuring the neutron flux density in the pulse range. The known method includes registration of neutrons by an ionization pulse-current fission chamber, three-level discrimination of the signal in amplitude, the formation of formalized pulses, the conversion of pulses into a code proportional to the number of pulses N _D from the discriminator, the formation of a signal in a PC proportional to the count rate of the pulse signal N _{OUT of} the fission chamber. In the method, in comparison with the previously described analogue, by using three-level discrimination of the signal by amplitude, the dynamic range of measuring the neutron flux density in the pulsed mode is expanded by correcting the miscalculations of pulses and taking into account double, triple overlaps of pulses arising at high N _input (above 10 ⁵ imp / s). Despite the increase in the measurement range of the neutron flux density in the pulsed mode, when switching from the pulsed measurement mode to the current one, in the range of N _ВХ above 10 ⁶ pulses / s, the measurement accuracy remains insufficient.

The disadvantages of the prototype can also be attributed to the complexity of the procedure for selecting the levels of discrimination. The insufficiently high accuracy and the complexity of the choice of discrimination levels are due to the fact that the authors, when taking into account the miscalculations of the pulses, take into account only two- and three-fold impulse overlaps, while with an increase in the load above 10 ⁶ pulses / s, the number of not only two- and three-fold overlays, but also four-, five-, etc. overlays. In addition, in addition to the influence of the channel load, the pulse duration τ _imp also affects the occurrence of pulse overlaps, which makes the selection of discrimination levels even more uncertain and laborious. The issue of accounting for miscalculations of pulses at different values of τ _{imp is} relevant, since various fission chambers (KNK-15-1, PIK-34, etc.) are widely used as part of the functioning channels for monitoring the neutron flux density (KNK-15-1, PIK-34, etc.), which at the output, due to their design features, form pulses of different duration. For example, the duration of the pulses generated by the KNK-15-1 is 120-150 ns, and the duration of the pulses from the suspension of the PIK-34 cameras is up to 350 ns. Using the method of mathematical modeling, the dependence of the fraction of multiple superposition of pulses in the signal of the fission chamber on the count rate was obtained for various values of τ of the _MFI : at a loading frequency of the measurement channel of the order of 1⋅10 ⁶ pulses / s, the proportion of superimposed (four or more) pulses with a duration of 120 does not amount to about ~ 1 %, and at τ _IMF = 350 ns ~ 3%; at a loading frequency of the order of 5⋅10 ⁶ pulses / s for the same τ _pulses 120 and 350 ns, - 10% and 65%, respectively; at a frequency of the order of download July ¹⁰ counts / s for 120 _pulses τ and 350 ns, the proportion imposed (four or more) pulses of 34% and 67%. To improve the accuracy, it is necessary to increase the number of discrimination levels, but this will lead to a complication of the device implementing the method, an increase in its dimensions and power consumption. It should be noted that for processing the pulse signal of the fission chamber, the discriminators and dividers that are part of the device implementing the prototype method are made on an element base that has high speed and, therefore, increased power consumption.

The present technical solution is aimed at solving these problems by creating a method for monitoring the neutron flux density of nuclear facilities. The technical result is to increase the accuracy and reliability of measuring the count rate of the pulse signal of the fission chamber in the range from 0.1 to 10 ⁷ pulses / s while monitoring the neutron flux density of nuclear facilities by reducing the loss of pulses due to miscalculations.

The problem is solved by the fact that in the method of measuring the density of the neutron flux by the ionization pulse-current fission chamber the neutron flux is recorded, and by means of the discriminator the pulse signal is discriminated in amplitude. Further, with the help of the shaper, the formation of formalized impulses is performed. Then, using a pulse converter, formalized pulses are converted into a code proportional to the number of pulses from the discriminator, and with the help of the control and processing unit, a signal is generated proportional to the count rate of the pulse signal of the fission chamber. According to the claimed technical solution, before generating a signal proportional to the count rate of the pulse signal of the dividing chamber, the number of pulses from the discriminator is adjusted, for which an adjustment unit is introduced, which includes an algorithm for calculating the count rate of the pulse signal of the dividing chamber according to the correction characteristic of the pulses' miscalculations, while the specified characteristic is dependence of the count rate of the pulse signal of the fission chamber on the number of pulses from the discriminator at different values of the load of the pulse measuring channel.

Additional variants of the method are possible, in which it is advisable that the count rate of the pulse signal of the fission chamber is determined by the formula:

- функция, определяющая значения числа импульсов с дискриминатора при различных значениях загрузки измерительного канала N_ВХ, имп/с;Where

- a function that determines the values of the number of pulses from the discriminator at different values of the loading of the measuring channel N _IN , imp / s;

- функция, определяющая величину просчетов импульсов с дискриминатора при различных значениях загрузки измерительного канала N_ВХ.

- a function that determines the amount of miscalculations of pulses from the discriminator at different values of the loading of the measuring channel N _IN .

является корректировочной характеристикой просчетов импульсов.Addiction

is a corrective characteristic of miscalculations of impulses.

A sign that distinguishes the proposed method from the prototype is the implementation of an additional procedure: adjusting the number of pulses N _D from the discriminator according to the correction characteristic of pulse miscalculations, which makes it possible to take into account the miscalculations of pulses, which increases the accuracy and reliability of the results of measuring the neutron flux.

The method for monitoring the neutron flux density of nuclear installations according to the invention is carried out as follows.

The neutron flux is recorded by an ionization pulse-current fission chamber. In the operating range, the transfer characteristic of the measuring channel should be linear (line 1, Fig. 1). With an increase in the load, the effect of overlapping pulses appears, which causes a deviation from the linearity of the transfer characteristic of the measuring channel, which uses a discriminator to process the camera signal, due to miscalculations (line 2, Fig. 1). Recalculate the impulses coming from the discriminator according to the formula of the form (1).

To implement the proposed method for monitoring the neutron flux density, the authors propose to make changes to the prototype device, which will significantly increase the accuracy and reliability of the results of measuring the count rate of the pulsed signal of the fission chamber when monitoring the neutron flux density of nuclear facilities and, in addition, significantly simplify the design of the device - prototype and reduce its power consumption.

A block diagram of a device that implements the proposed method is shown in Fig. 2, where the reference numbers indicate:

1 - pulse-current fission chamber,

2 - spectrometric amplifier,

3 - electrometric amplifier,

4 - amplifier signal-to-code converter,

5 - discriminator,

6 - shaper,

7 - converter count-code,

8 - correction block,

9 - control and processing unit.

The device operates as follows.

With an increase in the channel load from 0.1 ^{pulses / s to 10 7} pulses / s, pulses from the pulse-current fission chamber 1 through the isolating capacitor are fed to the input of the spectrometric amplifier 2. From the output of the spectrometric amplifier 2 amplified pulses are fed to the input of the discriminator 5. Discrimination level discriminator 5, as in the prototype, is equal to 0.3-0.5 of the nominal value of the amplified pulse. At the output of the discriminator, pulses are formed, which are fed to the shaper 6. The pulses from the discriminator 5 are formed in duration by the shaper 6 and are fed to the input of the counter-code 7 converter. into the block for correcting 8 miscalculations of pulses, where, according to a given algorithm, taking into account the correction characteristics, the count rate of the pulse signal N _OUT from the division chamber is calculated. At the output of the correction unit 8, a code is generated corresponding to the calculated value of N _OUT , which is fed through the line to the control and processing unit 9. where a signal is generated in the computer corresponding to the value of the pulse count rate N _OUT from the dividing chamber.

With a further increase in the channel load above 10 ⁷ pulses / s, it is advisable to carry out measurements according to the value of the current, which is supplied from the zero electrode of the ionization pulse-current chamber of dividing 1 to the input of the electrometric amplifier 3 and through the amplifier signal converter into code 4 and the line to the control unit and processing 9.

To implement the proposed method, the unit for calculating the count rate of the pulse signal of the fission chamber is proposed to be executed on the basis of a microprocessor, in the memory of which an algorithm for correcting miscalculations is wired. The high-voltage power supply units of the fission chamber, the amplifier and signal processing units of the fission chamber are manufactured at the Federal State Unitary Enterprise “NITI im. A.P. Aleksandrov "for delivery to nuclear power plants.

The applicant has developed documentation that describes the design of the device and its main technical characteristics. The device provides for the possibility of implementing the method for measuring the count rate, taking into account the developed algorithm for correcting the miscalculations of impulses.

At present, work is underway on the manufacture of a pulse-current meter, in which an algorithm for calculating the measured pulse count rate of the fission chamber by the correction characteristic of pulse counts is applied.

Thus, by reducing the loss of pulses due to improved measurement accuracy errors fission chamber pulse signal count rate from 0.1 to July ¹⁰ pulses / s, which allows to obtain reliable results of monitoring the neutron flux density of nuclear installations in a wide range, increase the level of protection reactor and increase the reliability and safety of its operation. In addition, this method makes it possible to expand the capabilities of the pulsed measuring channel in terms of its use not only for monitoring the neutron flux density in the composition of reactimeters, but also as a separate (specialized) device in fuel-element cladding tightness monitoring systems and in systems for measuring the flow rate of the water coolant in vessel-based nuclear reactors. , where the loading range of the registered activity N ¹⁷ does not exceed the value (1-1.5) ⋅10 ⁶ pulses / s.

Claims (5)

A method for controlling the density of the neutron flux, which consists in the fact that the neutron flux is recorded by the ionization pulse-current fission chamber, the discriminator is used to discriminate the pulse signal in amplitude, and with the help of the shaper, formalized pulses are formed, then the formalized pulses are converted into a code proportional to the number of pulses from the discriminator , and generate a signal proportional to the count rate of the pulse signal of the dividing chamber, characterized in that before generating a signal proportional to the count rate of the pulse signal of the dividing chamber, the number of pulses from the discriminator is corrected, for which a correction unit is introduced, which includes an algorithm for calculating the count rate of the camera pulse division according to the correction characteristic of pulse counts, while the specified characteristic is the dependence of the count rate of the pulse signal of the fission chamber on the number of pulses with discriminator at different values of the load of the impulse measuring channel. 2. The method according to claim 1, characterized in that the pulse count rate of the fission chamber signal is determined by the formula

Where

- a function that determines the values of the number of pulses from the discriminator at different values of the loading of the measuring channel N _IN , imp / s;

- a function that determines the amount of miscalculations of pulses from the discriminator at different values of the loading of the measuring channel N _IN .

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