A self-sufficient detector arrangement for a modular small pressurized water reactor

Abstract

The present application belongs to the technical field of nuclear reactor core, and particularly relates to a self-sufficient detector arrangement method suitable for a modular small-sized pressurized water reactor. The method comprises the following steps: determining the arrangement space of the self-sufficient detector in the assembly; establishing the influence function value of the self-sufficient detector at each different position; calculating the three-dimensional core calculation modeling by adopting the whole reactor neutron transport calculation; randomly establishing a three-dimensional arrangement scheme set of the self-sufficient detector, and obtaining the normalized theoretical current of the assembly where no measuring point is located; calculating the root mean square error of the relative deviation of the normalized theoretical current; setting the root mean square error acceptance limit value, and selecting the self-sufficient detector arrangement scheme with the least number of detectors and the root mean square error lower than the limit value as the optimal scheme. The beneficial effect lies in that the reasonable arrangement of the self-sufficient detector is realized in the limited space, so as to obtain the detector arrangement scheme satisfying the power distribution precision of the online monitoring.

Description

Technical Field

[0001] This invention belongs to the field of nuclear reactor core technology, specifically relating to a method for arranging self-powered detectors suitable for modular small pressurized water reactors. Background Technology

[0002] To ensure the economic efficiency and safety of power plant operation, safety parameters related to the integrity of fuel elements and cladding barriers must be monitored to ensure they do not exceed design limits. The two most important parameters are linear power density (LPD) and deviation from nucleus boiling ratio (DNBR). Commercial pressurized water reactor nuclear power plants employ a core power distribution monitoring system to monitor these two crucial parameters and ensure operational safety. This system typically comprises two parts: an external monitoring system and an internal monitoring system.

[0003] In the early stages of reactor development, nuclear power plants primarily used external monitoring systems, including detectors to measure loop coolant temperature and flow rate, and ionization chamber neutron detectors to detect neutron leaks. To prevent core DNB (density-to-temperature ratio) and fuel meltdown, over-temperature ΔT and over-power ΔT protection channels were typically implemented. These protection channels reflected the minimum DNBR and linear power density in the core through the temperature difference between the reactor inlet and outlet and readings from the external ionization chamber. However, external ionization chambers and thermal detection can only roughly estimate the power distribution within the reactor, resulting in significant errors. This necessitates a larger safety margin, which is detrimental to improving the economic efficiency and safety of the power plant.

[0004] With the maturation of nuclear power technology, power distribution monitoring systems based on in-core detectors have been applied. These systems use movable or fixed in-core detectors arranged in a specific manner to monitor the neutron flux (power) distribution within the reactor core, while thermocouples monitor internal thermal parameters. For movable detector systems, the external detectors (ionization chambers) are periodically calibrated. Real-time measurements from the external ionization chambers and in-core thermocouples are used to obtain power distribution and other parameters through a specific algorithm, achieving online monitoring and protection. For fixed in-core detector systems, continuous online monitoring of the core power distribution is convenient and more accurate and reliable. Fixed in-core detector systems directly monitor LPD and DNBR to ensure the integrity of fuel elements and cladding. Compared to over-temperature ΔT and over-power ΔT protection, the biggest advantage of in-core monitoring systems is the direct monitoring of local safety parameters related to the fuel cladding barrier. Therefore, they can more accurately describe the core's operating status, have lower computational uncertainty, and provide greater economic benefits and flexibility while ensuring safe operation.

[0005] Fixed in-core detector systems typically employ a limited number of self-powered detectors within the reactor core. Using the actual current signals as input, they perform necessary current-to-power conversion and power expansion calculations to derive the overall reactor power distribution, thus achieving reactor power distribution monitoring. Taking the VVER-1000 pressurized water reactor of Units 1 and 2 of a domestic nuclear power plant as an example, this reactor core consists of 163 fuel assemblies, with 54 detection channels arranged within the core. Each detection channel has 7 rhodium self-powered detectors equidistantly positioned along the axial direction. The measured current signals radiated throughout the entire reactor core are obtained through these detectors, thus providing the overall reactor power distribution.

[0006] Compared to large commercial pressurized water reactors, modular small pressurized water reactor cores have fewer fuel assemblies and smaller axial height. The challenge lies in how to rationally arrange a limited number of self-sufficient energy detectors within a limited space to obtain a detector arrangement scheme that meets the accuracy requirements for online monitoring of power distribution. Summary of the Invention

[0007] The purpose of this invention is to provide a method for arranging self-sufficient detectors suitable for modular small pressurized water reactors. By comparing and analyzing the influence function values ​​of self-sufficient detectors at different locations within the reactor core, and comparing and analyzing the theoretical calculations and reconstructed non-measuring point theoretical currents, the optimal arrangement of self-sufficient detectors under different numbers of detector measuring points can be obtained.

[0008] The technical solution of the present invention is as follows: A method for arranging self-sufficient energy detectors suitable for modular small pressurized water reactors, comprising the following steps: Step 1: Determine the placement space of the self-sufficient energy detector within the fuel assemblies used in the modular small pressurized water reactor. Step 2: Establish the influence function value of the self-powered detector at each different location; Step 3: The three-dimensional reactor core is modeled and calculated by using full-core neutron transport calculation. It is assumed that self-powered detectors are arranged in the central instrument tubes of all fuel assemblies in the core and are not spaced apart axially. The power distribution of the modular small pressurized water reactor core and the normalized information of the theoretical current at each position in the core are obtained through calculation. The normalized theoretical current is the normalized absorption reaction rate. Step 4: Randomly establish a three-dimensional arrangement scheme set of self-powered detectors, and use the influence function value of the self-powered detectors in Step 2 to obtain the normalized theoretical current of the components where the non-measuring points are located. Step 5: Using the normalized theoretical current of the component where the non-measuring point is located obtained in Step 3 as the reference solution, calculate the relative deviation of the normalized theoretical current of the component where the non-measuring point is located in Step 4, and calculate the root mean square error of the relative deviation of the normalized theoretical current. Step 6: Set the root mean square error (RMSE) acceptance limit, and select the self-powered detector layout scheme with the minimum number of detectors and the RMSE below the limit as the optimal scheme.

[0009] In step 1, the self-sufficient energy detector is placed inside the central instrument tube grid of the fuel assembly. For different fuel assembly types, the instrument guide tube is located at the exact center of the fuel assembly.

[0010] In step 1, the detector consists of multiple independent sensing elements connected in series and arranged uniformly at multiple points along the axial length of the fuel assembly. The number of sensing elements arranged axially is between 5 and 7.

[0011] Step 2 includes: using core physics calculation software to model the core of a modular small pressurized water reactor, assuming that no detectors are placed in the fuel assemblies, and performing whole-reactor neutron transport calculations to obtain the whole-reactor neutron flux or power distribution results.

[0012] Step 2 includes: introducing a perturbation at the location under investigation by inserting a detector into the instrument guide tube of the fuel assembly, and then performing a full-pile neutron transport calculation to obtain the full-pile flux or power distribution.

[0013] Step 2 includes: statistically analyzing the flux or power distribution results at different locations in the entire core before and after the perturbation, calculating the change in flux or power distribution at different locations in the core, and statistically converting the change into an attenuation function of the distance from the location under investigation. This attenuation function is the influence function of the self-powered detector at different locations.

[0014] Step 2 includes: by calculating the disturbance at different locations within the entire reactor core, obtaining the changes in flux or power distribution before and after the placement of self-powered detectors at different locations within the reactor core, as well as the influence function of the self-powered detectors.

[0015] Step 2 includes: summing the changes in component flux or power distribution before and after the self-powered detector is placed to 1.0 and normalizing them; selecting positions where the normalized change is greater than or equal to 0.01 to establish the influence domain of the component where the detector is located; and the normalized change in flux or power distribution of different fuel assemblies in the reactor core is the influence function value of the self-powered detector at each different position.

[0016] The beneficial effects of this invention are as follows: by influencing the function values ​​of self-sufficient detectors at different locations within the reactor core, the optimal arrangement scheme of self-sufficient detectors under different numbers of detector measurement points is obtained, thereby achieving a reasonable arrangement of self-sufficient detectors within a limited space, and obtaining a detector arrangement scheme that meets the accuracy requirements for online monitoring of power distribution. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the fuel assembly structure; Figure 2 A schematic diagram of the radial influence domain of the detection component; Figure 3 This is a diagram showing the channel layout of the neutron detector for core self-sufficiency. Figure 4 This is a schematic diagram showing the arrangement of axial detectors in the neutron detection channel and the corresponding axial layering of the reactor core. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] This invention provides a method for arranging self-sufficient detectors suitable for modular small pressurized water reactors. By comparing and analyzing the influence function values ​​of self-sufficient detectors at different locations within the reactor core, and comparing theoretical calculations with reconstructed non-measuring point theoretical currents, the optimal self-sufficient detector arrangement scheme is obtained for different numbers of detector measuring points. This allows for a reasonable arrangement of self-sufficient detectors within a limited space, achieving a detector arrangement scheme that meets the accuracy requirements for online power distribution monitoring. The specific steps include: Step 1: Determine the placement space of the self-sufficiency detector within the fuel assembly based on the fuel assembly used in the modular small pressurized water reactor. Taking the domestically produced CF3 truncated fuel assembly as an example, the self-sufficiency detector will be placed within the central instrumentation grid of the fuel assembly. Its radial position is determined by the instrumentation guide tube defined by the fuel assembly, i.e., at the center position, such as... Figure 1 As shown. For different fuel assembly types, the instrument guide tubes are all located at the exact center of the fuel assembly. To obtain a precise axial power distribution, the detectors are designed as multiple independent sensing elements connected in series, evenly distributed at multiple points along the axial length of the fuel assembly to cover the active region of the core. For example... Figure 4 As shown. The number of axially arranged sensitive elements varies depending on the type of fuel assembly, typically between 5 and 7.

[0020] Step 2: Establish the influence function value of the self-powered detector at each different location.

[0021] First, a modular small pressurized water reactor core model was created using core physics calculation software. The model took into account the actual arrangement of fuel assemblies, internal structural materials, and reflector layers. It was assumed that no detectors were placed in any of the fuel assemblies. The neutron transport calculation was performed to obtain the neutron flux (or power) distribution of the entire reactor. Secondly, by inserting a detector into the instrument guide tube of the fuel assembly, i.e. changing the material inside the guide tube, a perturbation is introduced to the location under investigation (the center of the assembly under investigation), and the neutron transport of the whole reactor is calculated again to obtain the flux (or power) distribution of the whole reactor. Next, the flux (or power) distribution at different locations in the entire reactor core before and after the perturbation is statistically analyzed, and the change in flux (or power) distribution at different locations in the reactor core is calculated. This change is then statistically converted into a decay function of distance from the location under investigation, which represents the influence function of the self-powered detector at different locations. Finally, by calculating the disturbance at different locations throughout the reactor core, the changes in flux (or power) distribution before and after the placement of self-powered detectors at different locations within the reactor core, as well as the influence function of the self-powered detectors, were obtained. The changes in flux (or power) distribution of the components before and after the placement of the self-powered detectors were summed to 1.0 and normalized. Locations with normalized changes greater than or equal to 0.01 were selected to establish the influence domain of the component containing the detector. The radial influence domain is illustrated below. Figure 2 As shown, the normalized variation of flux (or power) distribution of different fuel assemblies in the reactor core is the influence function value of the self-sufficient energy detector at each different location.

[0022] Step 3: A three-dimensional core model is constructed using full-core neutron transport calculations. The model considers the actual arrangement of fuel assemblies, internal structural materials, and reflectors. It is assumed that self-powered detectors are located within the central instrumentation tubes of all fuel assemblies, and that these detectors are not spaced out axially. The power distribution of the modular small pressurized water reactor core and the normalized theoretical current information at each location within the core are obtained through calculation. The theoretical current information at each location within the core is proportional to the absorption reaction rate of the sensitive element at that location; therefore, the normalized theoretical current is the normalized absorption reaction rate.

[0023] Step 4: Randomly establish a set of three-dimensional arrangement schemes for self-sufficient detectors. The radial arrangement of detectors in these schemes considers core axisymmetry, with the number gradually increasing from 4 to 24. The number of axially sensitive elements is considered in three uniform arrangements: 3, 5, and 7. For each detector arrangement, the influence function value of the self-sufficient detector from Step 2 is used to obtain the normalized theoretical current of the component not located at the measurement point. Step 5: Using the normalized theoretical current of the component where the non-measuring point is located obtained in Step 3 as the reference solution, calculate the relative deviation of the normalized theoretical current of the component where the non-measuring point is located in Step 4, and calculate the root mean square error of the relative deviation of the normalized theoretical current. Step 6: Set the root mean square error (RMSE) acceptance limit, and select the self-powered detector layout scheme with the minimum number of detectors and the RMSE below the limit as the optimal scheme.

[0024] Example: This embodiment describes the arrangement of the self-powered detectors in a modular small pressurized water reactor (SWR). The arrangement of the self-powered neutron detector channels in the SWR core is as follows: Figure 3 As shown, the axial detector arrangement of the neutron detection channel and the corresponding axial core layering are as follows: Figure 4As shown. The reactor core has 57 fuel assemblies, with a cold-state height of 215.0 cm for the active section. Ten neutron detection channels are arranged within the reactor, with five self-powered neutron detectors evenly spaced axially in each channel. The ten detection channels are divided into two groups of five channels each; the grouping of the detection channels is shown in the diagram. Figure 3 The bid was successful.

Claims

1. A method for arranging self-sufficient energy detectors suitable for modular small pressurized water reactors, characterized in that, Includes the following steps: Step 1: Determine the placement space of the self-sufficient energy detector within the fuel assemblies used in the modular small pressurized water reactor. Step 2: Establish the influence function value of the self-powered detector at each different location; Step 3: The three-dimensional reactor core is modeled and calculated by using full-core neutron transport calculation. It is assumed that self-powered detectors are arranged in the central instrument tubes of all fuel assemblies in the core and are not spaced apart axially. The power distribution of the modular small pressurized water reactor core and the normalized information of the theoretical current at each position in the core are obtained through calculation. The normalized theoretical current is the normalized absorption reaction rate. Step 4: Randomly establish a three-dimensional arrangement scheme set of self-powered detectors, and use the influence function value of the self-powered detectors in Step 2 to obtain the normalized theoretical current of the components where the non-measuring points are located. Step 5: Using the normalized theoretical current of the component where the non-measuring point is located obtained in Step 3 as the reference solution, calculate the relative deviation of the normalized theoretical current of the component where the non-measuring point is located in Step 4, and calculate the root mean square error of the relative deviation of the normalized theoretical current. Step 6: Set the root mean square error (RMSE) acceptance limit, and select the self-powered detector layout scheme with the minimum number of detectors and the RMSE below the limit as the optimal scheme.

2. The self-sufficient energy detector arrangement method applicable to modular small pressurized water reactors as described in claim 1, characterized in that: In step 1, the self-sufficient energy detector is placed inside the central instrument tube grid of the fuel assembly. For different fuel assembly types, the instrument guide tube is located at the exact center of the fuel assembly.

3. The self-sufficient energy detector arrangement method applicable to modular small pressurized water reactors as described in claim 2, characterized in that: In step 1, the detector consists of multiple independent sensing elements connected in series and arranged uniformly at multiple points along the axial length of the fuel assembly. The number of sensing elements arranged axially is between 5 and 7.

4. The method for arranging self-sufficient energy detectors suitable for modular small pressurized water reactors as described in claim 1, characterized in that, Step 2 includes: using core physics calculation software to model the core of a modular small pressurized water reactor, assuming that no detectors are placed in the fuel assemblies, and performing whole-reactor neutron transport calculations to obtain the whole-reactor neutron flux or power distribution results.

5. The method for arranging self-sufficient energy detectors suitable for modular small pressurized water reactors as described in claim 4, characterized in that, Step 2 includes: introducing a perturbation at the location under investigation by inserting a detector into the instrument guide tube of the fuel assembly, and then performing a full-pile neutron transport calculation to obtain the full-pile flux or power distribution.

6. The method for arranging self-sufficient energy detectors suitable for modular small pressurized water reactors as described in claim 5, characterized in that, Step 2 includes: statistically analyzing the flux or power distribution results at different locations in the entire core before and after the perturbation, calculating the change in flux or power distribution at different locations in the core, and statistically converting the change into an attenuation function of the distance from the location under investigation. This attenuation function is the influence function of the self-powered detector at different locations.

7. The method for arranging self-sufficient energy detectors suitable for modular small pressurized water reactors as described in claim 6, characterized in that, Step 2 includes: by calculating the disturbance at different locations within the entire reactor core, obtaining the changes in flux or power distribution before and after the placement of self-powered detectors at different locations within the reactor core, as well as the influence function of the self-powered detectors.

8. The method for arranging self-sufficient energy detectors suitable for modular small pressurized water reactors as described in claim 4, characterized in that, Step 2 includes: summing the changes in component flux or power distribution before and after the self-powered detector is placed to 1.0 and normalizing them; selecting positions where the normalized change is greater than or equal to 0.01 to establish the influence domain of the component where the detector is located; and the normalized change in flux or power distribution of different fuel assemblies in the reactor core is the influence function value of the self-powered detector at each different position.

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