Method for measuring value of control rod in nuclear reactor based on parameter inversion

Abstract

The invention provides a method for measuring the value of a control rod in a nuclear reactor based on parameter inversion, and the method comprises the steps: determining the nuclear cross section parameter of a reactor core region where the control rod to be measured is located, and further calculating the value parameter of the control rod to be measured, an actually measured detector signal in the process is recorded; a control rod to be detected is simulated to be inserted into a reactor core through a three-dimensional space-time dynamics program, corresponding analog detector signals are calculated, and the reactor core is divided into a plurality of basic calculation units with preset initial nuclear section parameters; judging whether the analog detector signal is consistent with the actually measured detector signal or not, if not, updating the nuclear cross section parameter of the basic calculation unit where the control rod to be detected is located, and recalculating the analog detector signal until the recalculated analog detector signal is consistent with the actually measured detector signal, and if yes, determining that the control rod to be detected is not consistent with the actually measured detector signal. And taking the nuclear cross section parameter finally used for calculation as the determined nuclear cross section parameter.

Description

Technical Field

[0001] The present invention relates to the technology of nuclear reactor physics experiments, and particularly to a method for measuring the worth of control rods in a nuclear reactor. Background Art

[0002] Control rods play a crucial role in the startup, shutdown, and power regulation of a reactor. For example, after a nuclear power plant replaces nuclear fuel, a startup test needs to be carried out, which is the main work during a major overhaul. Among them, the control rod worth measurement test is the main test item of the startup test and also the item that takes the longest time.

[0003] Early methods for measuring the worth of control rods included the boron dilution method, the rod exchange method, the neutron multiplication period method, etc. For example, in the boron dilution method, the control rod needs to be inserted downward at an extremely slow speed, and then the boron concentration in the moderator is adjusted to make the reactor critical. After the detector reading stabilizes, the reactivity is calculated. Therefore, the boron dilution method is a very long process. For example, in the rod exchange method, first, the group of control rods with the largest worth is calibrated by the boron dilution method. Then, taking this group of control rods as a reference, the group of rods to be measured is inserted, and at the same time, the reference rod group is slightly lifted to compensate for the negative reactivity introduced by the group of rods to be measured and maintain the critical state of the reactor core. After the detector reading stabilizes, the worth of the group of rods to be measured can be deduced based on the worth of the reference rods. The rod exchange method is slightly faster than the boron dilution method. However, it still takes about 2 hours to measure the worth of a group of rods, so it takes 1 - 2 days to measure all rod groups, which is still a significant time cost in this field.

[0004] In the 1990s, Westinghouse proposed a new rod engraving method called the Dynamic Rod Worth Measurement (DRWM). This method is based on the results calculated by the point reactor inverse dynamic formula. Using the inverse dynamic formula, it is very convenient to calculate the reactivity from the total core power. However, in the actual core arrangement, there are the following two error factors, which cause the detector signal not to correctly reflect the change in the total core power: (1) the influence of the spatial effect. When a control rod is inserted, it directly causes a change in the spatial distribution of prompt neutrons in the reactor core, so that the detector reading during the rod insertion process is not proportional to the total core power; (2) the influence of the delayed neutron effect. The spatial distribution of delayed neutrons changes more slowly than that of prompt neutrons. Therefore, the inverse dynamic formula obtains a "dynamic reactivity" in a certain sense, rather than the static reactivity we expect. To reduce the influence of the above effects, the aforementioned dynamic rod worth measurement method performs high-precision computer numerical simulation on the rod insertion process before the experiment to obtain the static spatial correction factor (SSF) and the dynamic spatial correction factor (DSF). During the experiment, the group of rods to be measured is inserted to the bottom at the maximum step rate, and the detector signals throughout the process are recorded. Then, by analyzing the detector signals, the integral worth and differential worth of the group of rods to be measured are obtained.

[0005] The dynamic rod calibration method significantly saves the time of rod calibration experiments. It only takes about 15 minutes to measure the worth of a group of rods. Currently, this method has been adopted by many countries. There will be differences in details when implemented on different reactor types, but the basic framework is based on the dynamic rod calibration method proposed by Westinghouse.

[0006] However, the known dynamic rod calibration methods perform poorly when introducing a large amount of reactivity in a short time, and there are deficiencies in the measurement accuracy of differential worth. At the same time, since it takes about 200 s for the control rod to be inserted from the top to the bottom of the core at the maximum step rate, on the one hand, the time consumption is still relatively long, and on the other hand, the detector count rate will decrease by two orders of magnitude during the rod insertion process, and the lowest will reach 10 -11 A, and noise will have a greater impact on the measurement results.

[0007] In addition, the prior art also knows the rod drop method for measuring reactivity or the worth of control rods. The common point of these methods is to directly drop the control rod to be measured into the core in a free-fall manner, and generally use the ratio of neutron count rates before and after the rod drop or the point reactor inverse dynamic formula for reactivity calculation. For example, the inverse dynamic formula is used for reactivity calculation in Chinese patent document CN100492547C, and the method of using static reactivity superposition of correction factors generated by the space-time kinetics program for reactivity calculation in CN109215822B. The known rod drop methods of this kind can only obtain the integral worth of the rod group to be measured, but cannot obtain the differential worth. Summary of the Invention

[0008] The purpose of the present invention is to propose a new method for measuring the worth of control rods, which should be able to measure the worth of control rods at a relatively fast speed and with high accuracy.

[0009] To this end, the present invention proposes a method for measuring the worth of control rods in a nuclear reactor. The method includes determining nuclear cross-section parameters related to the insertion depth of the control rod to be measured in the core region where the control rod to be measured is located, and calculating the worth parameter of the control rod to be measured based on the determined nuclear cross-section parameters. The step of determining the nuclear cross-section parameters includes: inserting the control rod to be measured into the core, and recording the time-related measured detector signals from the neutron detectors pre-arranged for this core during the process of inserting the control rod to be measured into the core; simulating the insertion of the control rod to be measured into the core through a three-dimensional space-time kinetics program, and calculating the corresponding time-related simulated detector signals, wherein the core is divided into several basic calculation units, and each basic calculation unit is preset with initial nuclear cross-section parameters; judging whether the simulated detector signal is consistent with the measured detector signal, and in the case of judging as inconsistent, updating the nuclear cross-section parameters of the basic calculation unit where the control rod to be measured is located and recalculating the simulated detector signal until the recalculated simulated detector signal is consistent with the measured detector signal, and taking the nuclear cross-section parameters finally used for calculating the simulated detector signal as the determined nuclear cross-section parameters.

[0010] It can be understood that the worth of a control rod is a measure of the change in core reactivity caused by the insertion of the control rod into the core, and the control rod affects reactivity by influencing the nuclear cross-section, especially the absorption cross-section, in the core region where it is located. The present invention proposes that in order to obtain the worth of a control rod, the influence of the control rod on the regional nuclear cross-section can be obtained first. The present invention proposes that by using known calculation tools including three-dimensional space-time kinetics programs, the changes related to core physics caused by the free fall of the control rod in the core can be simulated. Further, in combination with the understanding of neutron detectors, the signals generated by the neutron detectors can also be simulated. The present invention proposes that the target can be set to make the simulated detector signal conform to the measured detector signal, and the nuclear cross-section parameters related to the real-time position of the control rod to be measured in the core region where the control rod is located can be solved by an iterative method, and then the worth parameter of the control rod can be calculated.

[0011] Thus, the present invention provides a brand-new method for measuring the worth of a control rod.

[0012] In particular, the foregoing simulation of the control rod to be measured inserted into the core by a three-dimensional space-time kinetics program and the calculation of the corresponding time-dependent simulated detector signal can specifically include: performing a simulation by a three-dimensional space-time kinetics program to obtain the time-dependent simulated core power distribution corresponding to the simulated process of inserting the control rod to be measured into the core; obtaining the detector response function corresponding to the actually arranged neutron detector; and calculating the simulated detector signal based on the simulated core power distribution and the detector response function.

[0013] In particular, the foregoing judgment of whether the simulated detector signal conforms to the measured detector signal can specifically include: discretizing the simulated detector signal and the measured detector signal in time according to the same rule, and judging whether the norm of the difference between the simulated detector signal and the measured detector signal is less than a preset threshold. If it is less, it is determined that the simulated detector signal conforms to the measured detector signal, otherwise it is determined that the simulated detector signal does not conform to the measured detector signal.

[0014] In particular, the three-dimensional space-time kinetics program involved in the present invention is preferably configured to be suitable for processing numerical calculations related to the three-dimensional transient neutron diffusion equation.

[0015] In particular, the control rod to be measured is inserted into the core in a free-fall manner or a controlled propulsion manner.

[0016] In particular, the foregoing calculation of the worth parameter of the control rod to be measured based on the determined nuclear cross-section parameters can specifically include: for each depth of the control rod to be measured in the core, obtaining the corresponding nuclear cross-section parameters, thereby performing a static calculation of the core to obtain the static reactivity of the core, and calculating from the static reactivity of the core to obtain the worth parameter of the control rod to be measured.

[0017] In particular, the value parameters referred to in the present invention include differential value and / or integral value. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic flow chart of a rod insertion measurement test according to an embodiment of the present invention.

[0019] Figure 2 is a schematic calculation flow chart of determining nuclear cross-section parameters of the core region where the control rod is located according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] The following will introduce the specific embodiments and advantages of the present invention in conjunction with the accompanying drawings.

[0021] According to the present invention, a method for measuring the value of a control rod in a nuclear reactor includes: Step S1, determining nuclear cross-section parameters related to the insertion depth of the control rod to be measured in the core region where the control rod to be measured is located; Step S2, calculating the value parameter of the control rod to be measured based on the determined nuclear cross-section parameters.

[0022] According to the present invention, Step S1 may include two aspects of work: (1) Conducting an actual rod insertion measurement test (actual test), in which neutron detectors for the core are pre-arranged, operating to insert the control rod to be measured into the core, and recording the detector signals in time series corresponding to the whole process of inserting the control rod to be measured into the core (actual measured detector signals). (2) Conducting simulation calculations and iterative updates, wherein the core is divided into several basic calculation units, each basic calculation unit is preset with initial nuclear cross-section parameters, starting from the preset parameters, calling a three-dimensional space-time dynamics program to simulate the rod insertion scenario, and calculating the detector signals in time series in the simulated scenario (simulated detector signals), then determining whether the simulated detector signals are consistent with the actual measured detector signals, and in the case of determination of inconsistency, updating the nuclear cross-section parameters of the basic calculation unit where the control rod to be measured is located and recalculating the simulated detector signals, repeating this process until the recalculated simulated detector signals are consistent with the actual measured detector signals, and taking the nuclear cross-section parameters finally used for calculating the simulated detector signals as the determined nuclear cross-section parameters.

[0023] It can be understood that the first simulation calculation based on the preset parameters can be completed before the actual test. It can be understood that except for the unknown nuclear cross-section parameters to be obtained, other necessary scenario parameters for simulation are easily available (such as the size of the core), or some scenario parameters can be specified, such as the action mode of the control rod to be measured (such as free fall, step, etc.).

[0024] Please refer to Figure 1 , in Figure 1In the figure, an example process of conducting an actual rod insertion measurement test according to an embodiment of the present invention is shown in sequence from left to right. This process may be, for example: (1) Lift all control rods out of the core 1; (2) Select the control rod 10 to be measured, insert the selected control rod 10 into the core 1, and record the detector signals (measured detector signals) from the neutron detectors 2 pre-arranged for the core 1 over time as the control rod 10 moves from the top of the core to the bottom of the core; (3) Lift the control rod 10 out of the core to prepare for the measurement test of other control rods 20.

[0025] In the sense of the terms of the present invention, "control rod" does not distinguish between singular and plural. For example, the control rod 10 can be a single control rod or a group of control rods (also referred to as a "rod group"). Preferably, for safety reasons, to ensure the symmetry of the core power distribution, a group of symmetrically arranged control rods are inserted; however, the method proposed by the present invention can handle the case of power tilt distribution, so theoretically the present invention can measure a single control rod alone.

[0026] Figure 1 Only two or two groups of control rods are shown exemplarily, but there can be more control rods in practice. The measurement of each or each group of control rods is carried out in sequence according to the above process.

[0027] In some embodiments, the control rod 10 is inserted into the core 1 in a free-fall manner, so that the test time is significantly saved and the efficiency is improved. In some other embodiments, the control rod 10 is inserted into the core 1 in a controlled propulsion manner, for example, inserted at the maximum step rate. In principle, the present invention allows various rod insertion methods.

[0028] The neutron detector 2 can be any neutron detector, such as a proportional counter. In some embodiments, the neutron detector 2 can be used to measure, for example, the neutron flux density at a certain position in space. The neutron detector 2 is arranged inside and / or outside the core. There can be one or more neutron detectors 2.

[0029] The signal generated by the neutron detector 2 reflects the real-time condition of the core neutrons, and thus also reflects the working condition of the core. In particular, it is related to the real-time power distribution of the core.

[0030] In some embodiments, the neutron detector 2 is connected to a calculation and analysis unit (not shown) for information, and the calculation and analysis unit is configured to perform calculation and analysis processing on the signals from the neutron detector 2. In particular, the calculation and analysis unit is configured to call a three-dimensional space-time dynamics program. In particular, the calculation and analysis unit outputs the worth parameters of one or a group of control rods for the test, including differential worth and / or integral worth.

[0031] In some embodiments, the signal of the neutron detector 2 is time-discrete or is processed as time-discrete (e.g., by a computational analysis unit).

[0032] In some embodiments, the following processing is performed to remove the noise of the measured detector signal: perform a moving average and then perform a de-mean operation. The detector noise in the experiment is mainly divided into two parts. One is the background noise, which can be regarded as a constant value; the other is the Gaussian noise caused by counting fluctuations, etc. Use the moving average to filter the Gaussian noise, and then perform de-mean to obtain a signal with a mean of 0, so that the background noise can be filtered. It is worth mentioning that if the rod insertion is carried out in a free-fall manner, only 2 - 3 s is required for one rod insertion. Therefore, there is still a relatively high counting rate after the rod insertion, and it is less susceptible to noise.

[0033] Please refer to Figure 2 , Figure 2 which is a schematic diagram of the calculation process for determining the nuclear cross-section parameters of the core region where the control rod is located according to an embodiment of the present invention.

[0034] Basically, the exemplary calculation utilizes the simulation of the reactor operating state and the detector response, and attempts to solve the nuclear cross-section parameters of the core region related to the insertion depth of the control rod (or "rod position") through iteration. The iteration goal is to make the simulated detector signal basically conform to the measured detector signal.

[0035] This calculation includes using a three-dimensional space-time kinetics program 3. It is known in the art that three-dimensional space-time kinetics programs can be used to simulate and analyze complex physical processes inside nuclear reactors. In theory, any three-dimensional space-time kinetics program can be adopted in the present invention. For example, the program mentioned in the paper "Transient Nodal Green's Function Method and Its Coupling with Thermal-Hydraulics Research".

[0036] Exemplarily, the three-dimensional space-time kinetics program 3 divides the experimental core 1 into several basic calculation units (e.g., homogenized nodes). Here, it can be understood that the basic calculation unit is a spatial region, and its nuclear physical properties (e.g., the equivalent nuclear cross-section parameters of this region) are determined by its content (e.g., the fuel assemblies and control rods in the core). It can be understood that as the control rod is inserted into the core, the occupied space fraction of the control rod in the core will change, and thus the nuclear cross-section parameters of the basic calculation unit where the control rod is located will change.

[0037] In an embodiment of the present invention, the regional nuclear cross-section parameters corresponding to each rod position of the control rod are the quantities to be determined. Exemplarily, nuclear cross-section parameters are preset for each basic calculation unit, and other necessary parameters or settings are provided (such as spatial dimension parameters, control rod action modes, etc., which are easily consistent with the actual rod insertion test), so that the three-dimensional space-time kinetics program 3 can perform simulation calculations in reactor physics, especially simulating the rod insertion scenario and calculating the required reactor physics information.

[0038] Exemplarily, a time-dependent core power distribution (corresponding to the simulated process of inserting the control rod into the core) is calculated using the three-dimensional space-time kinetics program 3.

[0039] Exemplarily, the response function of the neutron detector 2 is obtained, which reflects the relationship between the detector signal and the core power distribution, especially the response of the detector signal to the core power distribution. It can be understood that the response function is determined by the nature of the neutron detector 2 itself and can be obtained by known methods in the art.

[0040] Therefore, combining the input response function, the response of the neutron detector 2 to the simulated core power distribution can be predicted, and thus the simulated detector signal corresponding to the simulated rod insertion process can be obtained.

[0041] The present invention also allows the simulated detector signal to be calculated by other unillustrated methods.

[0042] The simulated detector signal is compared with the aforementioned measured detector signal to determine whether the current simulated detector signal conforms to the measured detector signal. Among them, in the case of non-conformance, the nuclear cross-section parameters of the basic calculation unit where the control rod to be measured is located are updated and the simulated detector signal is recalculated. Repeat this process until the simulated detector signal conforms to the measured detector signal. The finally used nuclear cross-section parameters (generally, the preset parameters need to be iterated, and the last updated parameters are taken) are used as the finally determined nuclear cross-section parameters and output or stored as the calculation result.

[0043] Exemplarily, the simulated detector signal and the measured detector signal are discretized in time according to the same rule, so the time-dependent signal can be transformed into a finite-dimensional vector. On this basis, the difference between the simulated detector signal and the measured detector signal is calculated, and then the norm of the difference vector, such as the second-order norm (i.e., the root mean square error), is judged whether it is less than a preset threshold. Among them, when it is less than the threshold, it is considered that the current simulated detector signal conforms to the measured detector signal.

[0044] It can be understood that the calculation of the simulated detector signal based on the preset parameters can be carried out before the measurement test shown in Figure 1 That is, the initial value of the iteration is calculated in advance and stored to save computing power and improve efficiency.

[0045] Exemplarily, the update logic (search logic) of the nuclear cross-section parameter to be determined can adopt common optimization algorithms, such as Newton-type algorithms, or some heuristic algorithms, such as particle swarm algorithms, genetic algorithms, etc.

[0046] In particular, in some embodiments, the calculation process of determining the nuclear cross-section parameter in the present invention is mathematically equivalent to solving the following non-linear equations:

[0047]

[0048] where, represents the simulated detector signal, represents the measured detector signal, where Σ represents the nuclear cross-section parameter to be determined (especially the regional equivalent nuclear cross-section parameter), t represents time, r represents the neutron position vector, E represents the neutron energy, R(r, E, t) represents the response function of the detector, p(r, E, t) represents the power distribution of the reactor core, Φ(r, E, t) represents the neutron flux distribution of the reactor core, F represents the neutron production operator, L represents the neutron leakage operator, and S(r, E, t) represents the neutron source term. Other symbols not mentioned should be understood as the usual meanings in reactor physics.

[0049] It can be understood that Equation 1a corresponds to making the simulated detector signal conform to the measured detector signal as described above, Equation 1b corresponds to obtaining the simulated detector signal from the response function and the reactor core power distribution as described above, and Equation 1c corresponds to performing the simulation using the three-dimensional space-time dynamics program as described above.

[0050] It can be understood that the regional equivalent nuclear cross-section parameter Σ is related to the position (insertion depth) of the control rod in the reactor core.

[0051] Furthermore, to solve the above non-linear equations, a fully implicit difference scheme can be adopted for time discretization, and the time-discretized equations are in the form of:

[0052]

[0053] In some embodiments, the steps of determining the nuclear cross-section parameter to be determined in the present invention are equivalent to iteratively solving the above non-linear equations. Exemplarily, non-linear iterative methods such as the classical Newton method, chord method, Shamanskii method, etc. can be adopted.

[0054] In some embodiments, the nuclear cross-section parameter of the reactor core region where the control rod to be measured is partially inserted into the reactor core is calculated by correcting the end effect of the control rod. For example, assuming that the flux distribution Φ i-1 at time t i-1 has been obtained, and now it is necessary to solve the flux distribution Φ i at time t iand cross section Σ i We insert the control rod section into the segment It is calculated by flux weighting (conservation of reaction rate) and according to this cross section Solve for the next moment t i Flux distribution At this time, according to The flux weighting of the node section to be determined is obtained like It is considered to have converged at this time; otherwise, according to Solution According to calculate Until

[0055] Step S1 can thus be implemented.

[0056] According to the present invention, step S2 may specifically include: obtaining corresponding nuclear cross-sectional parameters for each position of the control rod to be tested in the core, thereby performing static calculation of the core to obtain the static reactivity of the core, and then further calculating the static reactivity of the core to obtain the value parameters (integral value and / or differential value) of the control rod to be tested.

[0057] The present invention can achieve the following advantages: (1) Since the calculation is performed with the help of a three-dimensional space-time dynamics program, there is no need to make a point-pile approximation, so the spatial effect caused by the movement of the control rod can be fully considered, and a higher-precision control rod value measurement result can be obtained; (2) In particular, compared with DRWM, the present invention allows the control rod to be tested to fall directly into the core, so that the time for measuring the test can be further shortened, which also avoids the situation where the detector count rate is too low and reduces the influence of noise; (3) Compared with the drop rod method known in the prior art, the present invention allows the integral value and differential value of the control rod to be tested to be obtained at one time.

[0058] Although some embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various combinations, changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for measuring the value of control rods in a nuclear reactor based on parameter inversion, the method comprising: Determine the nuclear cross-sectional parameters of the core region where the control rod to be tested is located and related to the insertion depth of the control rod to be tested; and Calculating the value parameters of the control rod to be tested based on the determined nuclear cross-section parameters; Wherein, the step of determining the nuclear cross-sectional parameters of the core region where the control rod to be tested is located and related to the insertion depth of the control rod to be tested comprises: Inserting the control rod to be tested into the reactor core, and recording the time-correlated measured detector signal from the pre-arranged neutron detector for the reactor core during the process of inserting the control rod to be tested into the reactor core; Simulating the insertion of the control rod to be tested into the core through a three-dimensional space-time dynamics program, and calculating the corresponding time-dependent simulated detector signal, wherein the core is divided into a number of basic calculation units, each of which is preset with an initial nuclear cross-section parameter; and Determine whether the simulated detector signal is consistent with the measured detector signal. If it is determined that they are not consistent, update the nuclear cross-section parameters of the basic calculation unit where the control rod to be measured is located and recalculate the simulated detector signal until the recalculated simulated detector signal is consistent with the measured detector signal. The nuclear cross-section parameters finally used to calculate the simulated detector signal are used as the determined nuclear cross-section parameters.

2. The method for measuring the value of control rods in a nuclear reactor according to claim 1, characterized in that: The method of simulating the insertion of the control rod to be tested into the core by a three-dimensional space-time dynamics program and calculating the corresponding time-related simulated detector signal includes: simulating by the three-dimensional space-time dynamics program to obtain a time-related simulated core power distribution corresponding to the simulated insertion process of the control rod to be tested into the core; obtaining a detector response function corresponding to the neutron detector; and calculating the simulated detector signal according to the simulated core power distribution and the detector response function.

3. The method for measuring the value of control rods in a nuclear reactor according to claim 1, characterized in that: The method of determining whether the simulated detector signal is consistent with the measured detector signal includes: time discretizing the simulated detector signal and the measured detector signal according to the same rule, and determining whether the norm of the difference between the simulated detector signal and the measured detector signal is less than a preset threshold value, if so, determining that the simulated detector signal is consistent with the measured detector signal, otherwise determining that the simulated detector signal is inconsistent with the measured detector signal.

4. The method for measuring the value of control rods in a nuclear reactor according to claim 1, characterized in that: The three-dimensional space-time dynamics program is suitable for processing numerical calculations related to the three-dimensional transient neutron diffusion equation.

5. The method for measuring the value of control rods in a nuclear reactor according to claim 1, characterized in that: The control rod to be tested is inserted into the core in a free-fall manner, or in a controlled-propulsion manner.

6. The method of measuring the value of control rods in a nuclear reactor according to claim 1, characterized in that: The method of calculating the value parameters of the control rod to be tested based on the determined nuclear cross-sectional parameters includes: obtaining the corresponding nuclear cross-sectional parameters for each depth of the control rod to be tested in the core, thereby performing static calculation of the core to obtain the static reactivity of the core, and calculating based on the static reactivity of the core to obtain the value parameters of the control rod to be tested.

7. The method of measuring the value of control rods in a nuclear reactor according to claim 1, characterized in that: The value parameter includes an integral value and / or a differential value.

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