RU2775730C1 - Method for calibration of the pulse channel of the reactimeter - Google Patents

Abstract

FIELD: nuclear technology.

SUBSTANCE: invention relates to the field of reactor measurements and can be used in control, control and protection systems of nuclear installations. Calibration of the counting channel of the reactimeter is performed in two stages. For the first stage of calibration, an experiment with nuclear reactor power excursion is used. The second stage of calibration is carried out in the post-processing mode of the results of monitoring the pulse counting rate and the current value of the pulse chamber signal.

EFFECT: increase in the efficiency and accuracy of calibration of the pulse channel of the reactimeter in the pulse range of the reactimeter from 0.1 s^-1 to (1-2)10⁶ s^-1 by performing calibration directly at a nuclear reactor during neutron-physical measurements without creating special conditions.

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Description

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

During the operation of a nuclear reactor (NR), in accordance with the requirements of regulatory documents to ensure nuclear safety (NS), it is required to periodically perform neutron-physical measurements (NPI), including to determine its reactivity characteristics (the effectiveness of regulatory bodies, coefficients and effects of reactivity ). Currently, to calculate the NR reactivity, digital reactimeters are used, which have sufficient speed and provide the possibility of visualizing processes in real time. One of the main requirements for the operation of the reactimeter is to ensure the calculation of reactivity in the widest possible power range of the nuclear reactor, which can be achieved using the pulse-current mode of its (reactor) operation.

Reactivity is calculated by digital reactimeters by the change in time of the signal from the ionization pulsed-current fission chamber (IC), which characterizes the neutron power of a nuclear reactor (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 (PNF) in location of the IC), by solving the inverted solution of the equations of NR kinetics (ORUK) [Kazansky Yu.A., Matusevich E.S. Experimental methods of reactor physics: Proc. allowance for universities. - M.: Energoatomizdat, 1984. - 272 p.]. At the same time, one of the important criteria for assessing the correctness of the reactimeter operation is the absence of “breakdowns” in the process of calculating the reactivity during transitions from the pulsed to the current mode and vice versa, for which overlap between the pulsed and current ranges must be provided.

The circuitry solutions implemented in the pulse channels of the reactimeters make it possible to raise the upper limit of the pulse range to the values of the count rate equal to (2-4)⋅10 ⁶ s ^-1 5⋅10 ^-13 C, corresponds to the current value in the current range, equal to approximately 5.5⋅10 ^-7 A. The lower limit of the current range is limited to (4-6)⋅10 ^-9 A, which corresponds to the value of the count rate in the pulse range , equal to approximately 5⋅10 ⁴ s ^-1 .

Thus, the reactimeter hardware provides more than 1 decade of overlap between the pulse and current measurement ranges: from 5⋅10 ⁴ s ^-1 to (2-4)⋅10 ⁶ s ^-1 in the pulsed mode and from (1-2) ⋅10 ^-9 A up to 5.5⋅10 ^-7 A in current.

Meanwhile, the operation of the reactimeter in the pulse mode is characterized by a violation of the linearity of the transfer characteristic of the counting channel at high loads. So, at a pulse count rate of approximately (3-5)⋅10 ⁵ s ^-1 , superimposed pulses appear in the IR signal, the proportion of which increases with increasing load, which leads to pulse miscalculations and, consequently, a significant distortion of the transfer characteristic linearity. This is especially evident during NFI, during which the operating mode of the reactimeter is switched from pulsed to current and vice versa (the range of change in the count rate is from 1⋅10 ⁶ s ^-1 to 2⋅10 ⁶ s ^-1 ), while “breakdowns” are observed reactivity calculations (see Fig. 1). In the range from 0.1 to (1-3)⋅10 ⁵ s ^-1, the effect of superposition of pulses is practically absent.

The transfer characteristic of the current channel of the ^reactimeter , with a relative error of no more than 3-4%, is linear in the range of 10 ^{-9 -10 -3} A. is due to the presence of a false output signal (dark current) in the output signals of the IR, the presence of which violates the linearity of the connection "neutron flux - chamber current", since it is caused by chamber currents from various types and origins of nuclear radiation, the intensity of which is not proportional to the neutron flux. The false output signal is mainly associated with the beta and gamma activity of fission products that accumulate in the uranium radiator of the IR during irradiation with IR neutrons. In this regard, in real conditions, the current channel can reliably control the PST in the nuclear reactor and calculate the reactivity with a relative error specified in the operational documentation in the range of 10 ^-8 -10 ^-3 A.

A known method of calibrating the pulse channel of the reactimeter [patent RU No. 2560531, publ. 07/22/2015], which includes control of the PPN in the NR core using a uranium fission chamber connected to the counting channel of the reactimeter, adjustment of the counting channel of the reactimeter depending on the reactivity calculated by the reactimeter, stabilization of the NR power at a fixed level, moving the NR control from one position to another in the direction corresponding to the decrease in POP. The disadvantage of this method is that the calibration is carried out only in the pulsed mode and does not take into account possible violations of the calculated reactivity during the transition from pulsed to current mode and vice versa.

A known method of calibrating the pulse channel reactimeter [patent RU No. 2653163, publ. 05/07/2018], selected as the closest analogue to the claimed invention, which includes control of the POP in the NR core using a uranium IR connected to the counting and current channels of the reactimeter uranium IR, moving the NR control from one position to another in the direction corresponding to a decrease in the POP and adjusting the pulse reactimeter channel in the pulse mode by adjusting the discrimination levels (second and third) in the area of reactimeter transition from current to pulse mode and vice versa.

The disadvantages of the closest analogue include the following:

- the uncertainty of the choice of discrimination levels, requires a large number of iterations to select the 2nd and 3rd levels of discrimination in order to obtain the specified accuracy characteristics of the linearity of the measuring channel, which implies a long calibration process;

- the need for the implementation of the method to create and maintain both special conditions and the operating mode of the NR, under which calibration is carried out, makes the entire procedure for calibrating the pulse channel of the reactimeter very expensive and not always feasible;

- calibration is carried out only in the area of switching between the current and pulse ranges and does not ensure the accuracy of the reactimeter setting in the entire range of the pulse mode of its operation.

This technical solution allows you to expand the arsenal of methods designed to calibrate the counting channel of the reactimeter, and is aimed at creating a method, the technical result of which, when implemented, will be a significant simplification, increase in efficiency and accuracy of calibration of the reactimeter pulse channel in the pulse range of the reactimeter from 0.1 from ^-1 to (1-2)⋅10 ⁶ s ^-1 due to the calibration directly at the nuclear reactor as part of the NFI, without creating special conditions.

The problem is solved by the fact that in the method of calibrating the counting channel of the reactimeter, which includes:

- control of the neutron flux density of a nuclear reactor (NR) using a detector reactimeter connected to the pulse and current channels, made on the basis of a uranium fission chamber (IR),

- stabilization of the reactor power at a fixed level, which corresponds to the initial critical state of the nuclear reactor,

- moving the regulatory body (RO) of the NR from one position to another, in accordance with the proposed technical solution, the calibration is performed in two stages as follows:

для первого этапа калибровки используют эксперимент с разгоном ЯР, при проведении которого:

for the first stage of calibration, an experiment with NR acceleration is used, during which:

- at the time t ₀ corresponding to the initial critical state of the RR, according to the readings of the pulse and current channels of the reactimeter, control and registration of the pulse count rate and the magnitude of the current of the IR signal begin,

- moving the nuclear reactor reactor from one position to another is performed in the direction corresponding to the increase in the power of the nuclear reactor, transferring it to a supercritical state, with a steady-state period of the reactor,

- fix the moment of time t _to when the IR current is at least 1.3-2 times greater than the value at which the reactimeter switches to the current mode of operation,

второй этап калибровки осуществляют в режиме постобработки результатов контроля скорости счета импульсов и величины тока сигнала ИК, при проведении которого:

the second stage of calibration is carried out in the mode of post-processing of the results of monitoring the pulse count rate and the magnitude of the IR signal current, during which:

- in the time interval from t ₀ to t _to the registered values of the pulse count rate and the magnitude of the current calculate the reactivity values for the pulse and current channels, respectively,

- compare the calculated values and determine the area where the reactivity values calculated from the readings of the pulse and current channels of the reactimeter coincide,

- in the selected area, the moment of time t ₁ is fixed, when the current of the impulse chamber is 3-5 times less than the value at which the reactimeter switches to the current mode of operation,

- then, in the time interval from t ₁ to t _k , the reactivity values calculated from the readings of the current channel are taken as calculated (or exemplary), and from them in the specified time interval, the calculated values of the count rate Ncalc are calculated, which are then used to determine the relative deviation of the readings of the calibrated pulse channel from the calculated value:

where ΔN(t _i ) is the value of the relative deviation of the readings of the calibrated pulse channel from the calculated value in the time interval from t ₁ to t _K , t _j =t ₁ , t ₁ +i⋅dt, …, t _K ; i=1, 2, …; dt - time readings;

N _meas (t _i ) - readings of the calibrated impulse channel in the time scale range from t ₁ to t _K , s-1,

N _pacch (t _i ) - the calculated value of the counting rate in the time interval from t ₁ to t _K , s-1,

- after that, the obtained values ΔN(t _i ) are approximated by the function of the dependence of the magnitude of relative deviations from the readings of the calibrated pulse channel in the form ΔN=ƒ _Δ (N _meas ), which in the count rate range from N _meas (t ₁ ) to N _meas (t _K ) is used to correct the readings of the calibrated pulse channel according to the formula:

where N _out =ƒ(N _meas ) - corrective characteristic miscalculations of pulses;

ƒ _Δ (N _meas ) - a function that determines the magnitude of pulse miscalculations at different values of the measurement channel load N _BX in the count rate range from N _meas (t ₁ ) to N _meas (t _k ), and in the count rate range up to N _meas (t ₁ )-N _out =N _meas .

Calculation of the values of reactivity in the pulse and current channels in the time interval from t ₀ to t _k can be performed by solving the inverse solution of the equations of NR kinetics, and to calculate the calculated values of the count rate Ncalc in the time interval from t ₀ to t _k , in particular, can the recurrence relation can be used:

where t _j =t ₀ , t ₀ +j⋅dt, …, t _K ; j=1, 2, …; dt - time readings;

λ _i is the decay constant of precursor nuclei of delayed neutrons of the i-th group;

and for the moments of time (t _j <t ₁ ) the normalization is accepted:

for time points (t _j ≥t ₁ ):

β is the total fraction of delayed neutrons; β _i - fraction of delayed neutrons of the i-th group of neutrons;

N _meas (t _j ) - counting rate of the pulse channel at the time t _j ;

ρ (N _meas (t _j )) is the reactivity calculated on the basis of the count rate N _meas (t _j ) over the pulse channel at the moment t _j ;

ρ (I(t _j )) is the reactivity calculated on the basis of the registration of the current I(t _j ) through the current channel at the moment t _j .

In addition, to determine N _calc (t) for time points (t _j ≥t ₁ ), the values of N _pacch (t _j ) and reactivity ρ (N _pacch (t _j ) obtained by computational simulation of the experiment with simulation of its conditions are taken.

Features that distinguish the proposed method from the prototype:

- for calibration, an experiment with the "acceleration" of the NR is used, while repeated experiments are not required;

- as the calculated values of the count rate, the values of the count rate calculated according to the ratio (3) according to the calculated values of reactivity are taken;

- as the calculated reactivity values, the reactivity values calculated by the ORUK method based on the results of measuring the IR current by the current channel of the reactimeter and (or) the reactivity values obtained by the calculation simulation of the experiment with imitation of its conditions can be taken;

- selection of the corrective characteristic is carried out in the mode of post-processing of the results of measuring the pulse count rate and current of the IR, respectively, by the counting and current channels of the reactimeter, obtained during the control of the PPN in the experiment with the "acceleration" of the NR.

The presented set of features ensures the achievement of the technical result, namely, it allows efficient and high-precision calibration of the pulse channel directly on the NR, significantly simplifies and reduces the time of calibration of the counting channel of the reactimeter.

The features of the present invention are explained by reference to the attached figure 2. The figure shows:

fig. 2a) - Reactivity calculated by the counting and current channels of the reactimeter when moving the controls in the direction of increasing power. The decrease in the reactivity calculated from the readings of the pulse channel is caused by an increasing proportion of miscalculations due to the effect of pulse superposition with an increase in load exceeding 10 ⁵ s ^-1 ;

fig. 2b) is a graphical illustration of the count rate measured by the IR signal, before calibration "n(t) count" and after "n(t) count (calculation)";

fig. 2c) is a graphical illustration of the detector current measured by the IR signal.

Calibration of the reactimeter pulse channel is performed as follows.

For the practical implementation of the proposed method, a wide-range pulsed current uranium fission chamber KNK-15-1 and a linear pulsed current meter "Favorite" operating in the reactimeter mode and manufactured by the Federal State Unitary Enterprise "NITI im. A.P. Alexandrova". The ionization pulse-current fission chamber, which controls the neutron flux density in a nuclear reactor, is connected to the pulse and current channels of the reactimeter. Bring the reactor to the power level, which corresponds to the initial critical state of nuclear reactor. At the time t ₀ corresponding to the initial critical state of the RR, according to the readings of the pulse and current channels of the reactimeter, control and registration of the pulse count rate and the magnitude of the IR signal current begin. The control element of the nuclear reactor is moved, transferring it to a supercritical state, with a steady-state period of the reactor. The moment of time t _K is fixed when the current IR is at least 1.3-2 times greater than the value at which the reactimeter switches to the current mode of operation t _I - _K (for the indicated IR and the Favorit meter, the time t _to corresponds to neutron detector current is approximately 2.4⋅10 ^-7 A). Further, in the time interval from t ₀ to t _K , according to the registered values of the pulse count rate and the current value, the reactivity values are calculated for the pulse and current channels, respectively, and the region is determined where the reactivity values calculated from the readings of the pulse and current channels of the reactimeter coincide. Shown in FIG. 2b) and c) the area where the coincidence of the reactivity calculated from the readings of the pulse and current channels (Fig. 2a)) corresponds to the range of measured count rate N=(1-3)⋅10 ^{5 s-1} and current strength I=(3 -5)⋅10 ^-8 A. In the selected area, the moment of time t ₁ is fixed when the current IR is 3-5 times less than the value at which the reactimeter switches to the current mode of operation t IR (when using _the specified IR and the Favorit meter » time t ₁ corresponds to the current of the neutron detector approximately 4⋅10 ^-8 A). In the time interval from t ₁ to t _K , the reactivity values calculated from the readings of the current channel are taken as calculated (or exemplary), and then, according to the exemplary reactivity values in the specified time interval, the recursive relation (3) calculates the calculated values Ncalc, s using which and Nmeas by formula (1) are calculated ΔN(t _i ). The obtained values of ΔN(t _i ) in the time range from t ₁ to t _K are approximated by the function of the dependence of the magnitude of relative deviations from the readings of the calibrated pulse channel N _meas (t _i ) in the form ΔN=ƒ _Δ (N _meas ), which then, in the speed range counts from N _meas (t _i ) to N _meas (t _K ) are used to correct the readings of the calibrated pulse channel according to formula (2), and in the count rate range up to N _meas (t ₁ )-N _out =N _meas .

When implementing the calibration method to determine N _calc (t) for time points (t _j ≥t ₁ ), the values of N _calc (t _j ) and reactivity ρ (N _calc (t _j )) can also be taken; obtained by computational modeling of the experiment with imitation of its conditions: the change in the POP in the core of the nuclear reactor and at the location of the IC is simulated.

The proposed calibration method was successfully verified by the calculation and experimental method, in which the calibration of the Favorit meter was performed using the SAPFIR_95&RC ^© software package, which simulates the conditions of the experiment. Also, the calibration method was experimentally tested when setting up the Favorit meter on the operating stand of the Federal State Unitary Enterprise NITI im. A.P. Aleksandrov” during a series of experiments of the same type with the section of “acceleration”. The correction characteristic obtained from the results of the first experiment was written into the external software of the Favorit meter and, without changes and additional adjustments, was used in the control of the PPN in all subsequent experiments. As a result, the transition from the pulse to current mode of operation of the reactimeter and vice versa was provided in real time, while the confirmed range of linearity of the transfer characteristic of the counting channel of the reactimeter from 0.1 to 9.81⋅10 ⁶ s ^-1 was achieved.

The proposed calibration method is confirmed by both computational and experimental verification, its application expands the arsenal of existing methods for calibrating the pulse channels of reactimeters, makes it possible to significantly simplify and reduce the time of the calibration procedure carried out directly on the NR, while increasing its efficiency and accuracy. The method is applicable to a wide range of overclocking experiments.

Claims (40)

1. A method for calibrating the reactimeter pulse channel, including monitoring the neutron flux density of a nuclear reactor (NR) using a detector connected to the pulse and current channels of the reactimeter, made on the basis of a uranium fission chamber (IC), stabilizing the reactor power at a fixed level, which corresponds to the initial critical state of the NR, moving the regulatory body (RO) of the NR from one position to another, characterized in that for calibration, an experiment is carried out with the acceleration of the NR, during which, at the time t ₀ corresponding to the initial critical state of the NR, according to the readings of the pulse and current channels of the reactimeter, control and registration of the pulse count rate and the magnitude of the current of the IR signal begin; the movement of the RR NR from one position to another is performed in the direction corresponding to the increase in the NR power, transferring it to a supercritical state with a steady-state period of the reactor, and fix the moment of time t _to when the IR current is at least 1.3-2 times greater than the value at which the reactimeter switches to the current mode of operation, then post-processing of the results of monitoring the pulse counting rate and the magnitude of the current of the IR signal is performed, for which in the time interval from t ₀ to t _K , according to the registered values of the pulse count rate and the current value, the reactivity values are calculated for the pulse and current channels, respectively, compare the calculated values and choose the area where the reactivity values calculated from the readings of the pulse and current channels of the reactimeter coincide, then, in the selected area, the moment of time t ₁ is fixed, when the current of the impulse chamber is 3-5 times less than the value at which the reactimeter switches to the current mode of operation, in the time interval from t ₁ to t _K , the reactivity values calculated from the readings of the current channel are taken as calculated, and from them, in the specified time interval, the calculated values of the count rate Ncalc are calculated, which are then used to determine by the formula

the magnitude of the relative deviation of the readings of the calibrated pulse channel from the calculated value in the time interval from t ₁ to t _K , where t _i =t _1, t ₁ +i⋅dt, …, t _K ; i=1, 2, …; dt - time readings; N _meas (t _i ) - readings of the calibrated impulse channel in the time scale range from t ₁ to t _K , s-1, N _pacch (t _i ) - the calculated value of the counting rate in the time interval from t ₁ to t _K , s ^-1 , after which the obtained _{values of ΔN ( t i} ) are approximated by the function of the dependence of the magnitude of relative deviations from the readings of the calibrated pulse channel in _the form used to correct the readings of the calibrated pulse channel according to the formula:

where N _out =ƒ(N _meas ) - corrective characteristic miscalculations of pulses; ƒ _Δ (N _meas ) - a function that determines the magnitude of pulse miscalculations at different values of the measurement channel load N _BX in the count rate range from N _meas (t ₁ ) to N _meas (t _k ), and in the count rate range up to N _meas (t ₁ )-N _out =N _meas . 2. The method according to claim 1, characterized in that the reactivity values for the pulse and current channels in the time interval from t ₀ to t _K are calculated by solving the inverted solution of the NR kinetics equations. 3. The method according to p. 1, characterized in that the calculated values of the count rate N _calc in the time interval from t ₀ to t _K are calculated according to the recurrence relation:

where t _j =t ₀ , t ₀ +j⋅dt, …, t _K ; j=1, 2, …; dt - time readings;

λ _i is the decay constant of precursor nuclei of delayed neutrons of the i-th group;

ϕ _i =1-E _i ; ψ _i =A _i -E _i ; and for the moments of time (t _j <t ₁ ) the normalization is accepted: N _calc (t _j )=N _meas (t _j );

for time points (t _j ≥t ₁ ):

β is the total fraction of delayed neutrons; β _i - fraction of delayed neutrons of the i-th group of neutrons; N _meas (t _j ) - counting rate of the pulse channel at the time t _j ; ρ (N _meas (t _j )) is the reactivity calculated on the basis of the count rate N _meas (t _j ) over the pulse channel at the moment t _j ; ρ (I(t _j )) is the reactivity calculated on the basis of the registration of the current I(t _j ) through the current channel at the moment t _j . 4. The method according to p. 1, characterized in that to determine N _pacch (t) for time points (t _j ≥t ₁ ) take the values of N _pacch (t _j ) and reactivity ρ (N _calc (t _j )) obtained by computational modeling of the experiment with imitation of its conditions.

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