A method for measuring reactivity based on subcritical physical experiment

Abstract

The present application belongs to the technical field of nuclear power plant core physics test, and particularly relates to a reactivity measurement method based on subcritical physics test. The method comprises the following steps: S10, critical physics test; S20, numerical simulation test; S30, data analysis and processing. The beneficial effect is that the critical state point obtained in the critical process is used to correct the model error in the core numerical simulation, the spatial correction factor, the 1 / M reactivity calibration curve are generated through the numerical model, the model error of each core state point is eliminated through the boron value equivalent method, and the experimental data are processed through the iteration method, so that the control rod value, the boron differential value or the moderator isothermal temperature coefficient and the like can be calculated from the obtained data, the physics test time can be shortened by about 8 hours, and the power generation efficiency of the unit is improved.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power plant core physics testing technology, specifically relating to a reactivity measurement method based on subcritical physics testing. Background Technology

[0002] Control rod value, boron differential value, and moderator temperature coefficient are core physical parameters that affect reactor safety, control, and operation. They must be measured through specialized zero-power tests. The common practice for pressurized water reactor units is to conduct zero-power physical tests based on a "point reactor model" after the reactor reaches criticality following refueling. This requires 8 to 12 hours of main unit overhaul time. During the test, a power range needs to be connected for use by the reactivity meter.

[0003] The current testing method has two problems: firstly, it increases the risk of reactor shutdown by occupying one power range; secondly, it occupies the critical path for unit overhaul and affects the unit's output. Summary of the Invention

[0004] The purpose of this invention is to provide a reactivity measurement method based on subcritical physics tests. After the critical physics test is completed, the critical state points obtained from the actual critical physics test are first used to correct the model error in the core numerical simulation. The corrected numerical model is then used to simulate the critical process, generating the source range simulated count rate and correction factor for each state point, and producing the corrected 1 / M extrapolation curve. Then, the correction factor is applied to the actual count rate measured by the source range, and the subcriticality of each state point is measured from the corrected 1 / M extrapolation curve. Based on the changes in state parameters between each state point, the control rod value, boron differential value, or moderator isothermal temperature coefficient, etc., are obtained.

[0005] The technical solution of the present invention is as follows: A reactivity measurement method based on subcritical physical experiments, comprising the following steps:

[0006] S10: Critical physical test;

[0007] In S10, critical physical experiments are conducted to obtain the state parameters, the reciprocal of the count rate, the critical boron concentration, and the critical rod position for each state.

[0008] S20: Conduct numerical simulation experiments;

[0009] S20 includes:

[0010] (1) Correction of the numerical model;

[0011] (2) The making of a reactive ruler;

[0012] (3) Construction of the correction factor table;

[0013] The numerical model is modified by giving a critical rod position, obtaining the boron concentration through a critical search, and then subtracting the deviation of the critical boron concentration when performing numerical simulations on all state points. ;

[0014] S30: Data analysis and processing;

[0015] S30 includes:

[0016] (1) First, assume that the calculated boron value and rod value are accurate. For each state point, the correction factor is: The corrected reciprocal of the count rate ;

[0017] (2) Normalized coefficient of the reciprocal of the count rate

[0018] For two adjacent states where only the boron concentration changes ,have

[0019] ,

[0020] Obtain the normalized coefficients Then, it applies to all state points. middle;

[0021] (3) According to The value, from Measure the subcriticality under each state;

[0022] (4) Iterate and calculate the deviation of the next critical degree for each state point. and equivalent to For each state point ,from Interpolation is used to update the correction factor, and the normalized coefficients are updated accordingly.

[0023] ,

[0024] in, The relative deviation between the measured and calculated values ​​of boron;

[0025] Repeat the above process, updating the measured values, until convergence.

[0026] The state parameters include moderator temperature, control rod position, and boron concentration.

[0027] The reactive ruler was fabricated by numerically simulating the state point in a critical physics experiment, where the boron concentration was taken as... The control rod position is consistent with the experimental position; the ruler that produces reactivity after correction for each state action, i.e. Linear relationship.

[0028] The aforementioned correction factor table is created by converting the deviation between the reactivity of the numerical model and the actual core at each state point into an equivalent boron concentration deviation. For each core state point, the deviation is calculated based on its baseline boron concentration. Simulations were performed on the above, followed by the perturbation of boron concentration. Simulations were performed to obtain the spatial correction factor as a function of the change in boron concentration at each state point. .

[0029] The beneficial effects of this invention are as follows: This method uses the critical state points obtained during the critical process to correct the model errors in the core numerical simulation. It generates spatial correction factors and 1 / M reactivity scale curves through the numerical model, eliminates model errors at each core state point through the boron value equivalence method, and processes experimental data through iterative methods to calculate the control rod value, boron differential value, or moderator isothermal temperature coefficient, etc. This can shorten the physical test time by about 8 hours and improve the unit's power generation efficiency. Attached Figure Description

[0030] Figure 1 A diagram showing the core locations primarily detected by the external source range;

[0031] Figure 2 The "convex and concave" characteristic curve of the 1 / M extrapolation curve;

[0032] Figure 3 This is a flowchart of the numerical simulation experiment.

[0033] Figure 4 Continuation 1: Numerical simulation experiment flowchart;

[0034] Figure 5 The flowchart for the numerical simulation experiment continues in part 2. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] The neutron source in a reactor acts as an "ignition" point at criticality. Neutrons emitted from the source multiply continuously within the reactor core, eventually reaching a stable state. At this stable state, the total number of neutrons in the core depends on the subcriticality of the core. The external source range primarily detects fast neutrons leaking from the side of the core closer to its location (such as...). Figure 1As shown in the diagram, the source range count rate is related not only to the total number of neutrons in the core but also to the shape of the neutron flux distribution. During the process of reaching criticality in a reactor, changes in control rod position, core boron concentration, and coolant temperature not only cause changes in the core subcriticality but also in the neutron flux distribution, leading to changes in the source range count rate. Therefore, to ensure that the source range count rate truly reflects the reactor core subcriticality, the contribution of neutron flux shape changes to the count rate must be eliminated, i.e., the "space effect" must be eliminated. The current 1 / M criticality extrapolation method utilizes the linear relationship between the reciprocal of the source range count rate and the core subcriticality under the assumption of a "point reactor model" for criticality monitoring. In the "point reactor model," the reactor is considered a point without spatial dimension, meaning that the neutron flux distribution within the reactor core is always in the shape of the critical state and does not change with the core state. Therefore, the 1 / M criticality extrapolation method does not eliminate the space effect but rather ignores it. However, in reality, the point reactor model only holds true when the reactor is close to criticality; it does not hold true at deep subcritical conditions (where strong space effects exist). Under a given core loading scheme, the relative position between the neutron source and its range determines the "convexity / concavity" characteristics of the 1 / M extrapolation curve (e.g., ...). Figure 2 (As shown).

[0037] If the space effect can be eliminated by introducing a correction factor, then the corrected 1 / M critical extrapolation curve and the core subcriticality will have a completely linear relationship, thus becoming a "ruler" for reactivity measurement. By applying the corresponding correction factor to the source range count measured under each core condition, reactivity can be measured from this "ruler," thereby obtaining the control rod value, boron differential value, and moderator isothermal temperature coefficient, etc. This correction factor can be generated through numerical simulation experiments using relevant core physics analysis software; in this application, the analysis software and the analysis object are collectively referred to as the numerical model.

[0038] This invention provides a reactivity measurement method based on subcritical physics tests. After the critical physics test is completed, the critical state points obtained from the actual critical physics test are first used to correct the model error in the core numerical simulation. The corrected numerical model is then used to simulate the critical process, generating the source range simulated count rate and correction factor for each state point, and producing the corrected 1 / M extrapolation curve. Then, the correction factor is applied to the actual count rate measured by the source range, and the subcriticality of each state point is measured from the corrected 1 / M extrapolation curve. Based on the changes in state parameters between each state point, the control rod value, boron differential value, or moderator isothermal temperature coefficient, etc., are obtained.

[0039] The experimental data required for this invention includes the final critical state point (critical boron concentration and critical rod position) of the critical physics experiment, the core state during the critical process (moderator temperature, control rod position, and boron concentration), and the source range count rate after stabilization at each core state. For numerical simulation, core design software is needed to simulate the core physics parameters (critical boron concentration, subcriticality, and fission rate distribution at each core state) during the experiment, and a response function for the external source range is needed to generate the simulated source range count rate for each core state.

[0040] In the absence of an external neutron source, the neutron transport equation can be written as follows:

[0041] (1)

[0042] In the formula, For the neutron extinction operator, Operators are generated for fission neutrons; Effective proliferation coefficient, defined as

[0043] (2)

[0044] Represents the integral operator in phase space;

[0045] Neutron transport equations under external neutron source conditions

[0046] (3)

[0047] In the formula, It is an external neutron source.

[0048] Define the neutron multiplication coefficient under exogenous conditions.

[0049] (4)

[0050] Under external neutron source conditions, the total number of neutrons in the reactor Substituting (4) into the equation, we get...

[0051] (5)

[0052] Since integration is performed in phase space, equation (5) is a point-heap model, which reveals... and The inverse relationship between them, that is and It is linear. But no , and It is not linear.

[0053] Equation (5) can be further written as

[0054] (6)

[0055] definition The external neutron source spatial correction factor essentially reflects the difference between the value of external neutron sources and the value of fission neutrons.

[0056] like effect Then, its reciprocal and It exhibits a linear relationship, that is

[0057] (7)

[0058] For the off-site source range detector, the count rate is:

[0059] (8)

[0060] In the formula, This is the detector response function.

[0061] Equation (8) can be further written as

[0062] (9)

[0063] According to equation (4) Definition, Substituting into equation (9), we get

[0064] (10)

[0065] definition If the source range space correction factor is used, then

[0066] (11)

[0067] External neutron source space correction factor Source range space correction factor The two can be combined into one, defining the total spatial correction factor.

[0068] (12)

[0069] Source range counting effect Then, its reciprocal and A linear relationship exists; this is the measure of quantitative responsiveness.

[0070] (13)

[0071] Key aspects of this invention include: using critical state points obtained from critical physics experiments to correct model errors in core numerical simulations; using numerical models to generate spatial correction factors and 1 / M reactivity calibration curves; using the boron value equivalence method to eliminate model errors at each core state point; using iterative methods to process experimental data; and introducing two groups of cross-section correction factors to account for the influence of secondary neutron sources on the core energy spectrum. This method can calculate control rod values, boron differential values, or moderator isothermal coefficients based on parameters during the critical process.

[0072] A reactivity measurement method based on subcritical physical experiments includes the following steps:

[0073] S10: Critical Physical Test

[0074] Critical physics experiments were conducted using methods commonly used in the prior art to obtain state parameters (moderator temperature, control rod position, and boron concentration), the reciprocal of the count rate, and the critical boron concentration CBcr,mea and critical rod position Rodstepcr,mea for each state. mea represents the measurement.

[0075] S20: Conduct numerical simulation experiments

[0076] (1) Correction of numerical model

[0077] Given the critical rod position Rodstepcr,mea, the boron concentration is obtained through a criticality search. Due to biases in the numerical model, CBcr,mea and CBcr,calc differ. Therefore, the numerical model needs to be corrected; that is, the bias in the critical boron concentration needs to be subtracted when performing numerical simulations for all state points.

[0078] (2) Making a reactive ruler

[0079] Numerical simulations were performed at the state points in the critical physics experiment, where the boron concentration was taken as... To ensure consistency between the position of the control rod and that of the test rod, a correction factor is generated according to equation (12). The reactive ruler is generated after correction for each state action, i.e. Linear relationship.

[0080] (3) Construction of the correction factor table

[0081] The correction factor is related to the subcritical state of the core. Although the critical state (boron concentration and control rod position) of the numerical model is corrected through the model in (1), the correction factor generated in (2) is not completely consistent with the correction amount required by the actual core due to the deviation between the rod value, boron value, and moderator temperature coefficient of the numerical model and the actual core. To this end, the present invention proposes a boron value equivalence method, that is, the deviation between the reactivity of the numerical model and the reactivity of the actual core at each state point is equivalently converted into the equivalent boron concentration deviation. For each core state point, in addition to its basic boron concentration, In addition to performing the simulation, it is also necessary to adjust the boron concentration after the perturbation. Simulations were performed. This allows us to obtain the spatial correction factor as a function of the change in boron concentration at each state point. .

[0082] S30: Data Analysis and Processing

[0083] Let's assume the calculated boron and rod values ​​are accurate. Then, for each state point, the correction factor is: The corrected reciprocal of the count rate ;

[0084] In the formula, ICRR represents the countdown rate.

[0085] Reciprocal normalized coefficient of count rate

[0086] Since the calculated boron value is assumed to be correct, for two adjacent states where only the boron concentration changes... ,have

[0087] ,

[0088] Obtain the normalized coefficients Then, it applies to all state points. middle.

[0089] In the formula, 1 / M m This represents the countdown rate at state point m; k is the increment coefficient.

[0090] according to The value, from Measure the subcritical degree under each state.

[0091] Iteration;

[0092] Calculate the deviation of the next criticality at each state point. (The deviation between the numerical simulation and the measurement of the subcritical degree), and equate it to For each state point ,from Interpolation is used to update the correction factor, and the normalized coefficients are updated accordingly.

[0093] ,

[0094] In the formula, The deviation between the numerical simulation and the measured boron concentration; This represents the deviation between the numerical simulation and the measurement of the subcritical degree. Among them, The relative deviation between the measured and calculated values ​​of boron;

[0095] Repeat the above process, updating the measured values, until convergence.

Claims

1. A reactivity measurement method based on subcritical physical experiments, characterized in that, Includes the following steps: S10: Critical physical test; In S10, critical physical experiments are conducted to obtain the state parameters, the reciprocal of the count rate, the critical boron concentration, and the critical rod position for each state. S20: Conduct numerical simulation experiments; S20 includes: (1) Correction of the numerical model; (2) The making of a reactive ruler; (3) Construction of the correction factor table; The numerical model is modified by giving a critical rod position, obtaining the boron concentration through a critical search, and then subtracting the deviation of the critical boron concentration when performing numerical simulations on all state points. ; S30: Data analysis and processing; S30 includes: (1) First, assume that the calculated boron value and rod value are accurate. For each state point, the correction factor is: The corrected reciprocal of the count rate ; (2) Normalized coefficient of the reciprocal of the count rate For two adjacent states where only the boron concentration changes ,have ， Obtain the normalized coefficients Then, it applies to all state points. middle; (3) According to The value, from Measure the subcriticality under each state; (4) Iterate and calculate the deviation of the next critical degree for each state point. and equivalent to For each state point ,from Interpolation is used to update the correction factor, and the normalized coefficients are updated accordingly. ， in, The relative deviation between the measured and calculated values ​​of boron; Repeat the above process, updating the measured values, until convergence.

2. The reactivity measurement method based on subcritical physical experiments as described in claim 1, characterized in that: The state parameters include moderator temperature, control rod position, and boron concentration.

3. The reactivity measurement method based on subcritical physical experiments as described in claim 1, characterized in that: The reactive ruler was fabricated by numerically simulating the state point in a critical physics experiment, where the boron concentration was taken as... The control rod position is consistent with the experimental position; the ruler that produces reactivity after correction for each state action, i.e. Linear relationship.

4. The reactivity measurement method based on subcritical physical experiments as described in claim 1, characterized in that: The aforementioned correction factor table is created by converting the deviation between the reactivity of the numerical model and the actual core at each state point into an equivalent boron concentration deviation. For each core state point, the deviation is calculated based on its baseline boron concentration. Simulations were performed on the above, followed by the perturbation of boron concentration. Simulations were performed to obtain the spatial correction factor as a function of the change in boron concentration at each state point. .

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