Method for inspecting power distribution symmetry of asymmetrically loaded hexagonal reactor core of nuclear power plant
By monitoring the reliability and relative deviation of the power peak factor Kq of the fuel assembly, combined with the division of symmetric groups and adjustment of evaluation standards, the power distribution inspection problem of asymmetric loading hexagonal cores is solved to ensure the safety and stability of nuclear power plant reactors.
Patent Information
- Application Number
- CN202510452573.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-11
- Publication Date
- 2025-08-15
AI Technical Summary
In nuclear power plants, the power distribution of asymmetrically loaded hexagonal core cannot be effectively checked, making it difficult to ensure the safety and stability of the reactor operation.
By monitoring the reliability and relative deviation of the power peak factor Kq of the fuel assembly, combined with the division of symmetric groups and evaluation criteria to determine the symmetry of the core power distribution to ensure safe operation of the reactor.
A method is provided to check the symmetry of the power distribution of asymmetric loaded hexagonal cores, improving the operating safety and reliability of the nuclear power unit, ensuring that the reactor operates in a safe state.
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Figure CN120496902A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of operation and safety of nuclear power plant reactors, and particularly relates to a method for checking the symmetry of power distribution of an asymmetrically loaded hexagonal core in a nuclear power plant. Background Art
[0002] According to national nuclear safety regulations, during the operation of pressurized water reactor (PWR) nuclear power units, regular checks of core power and its distribution are required to ensure they are within appropriate operating limits and conditions to assess the reactor's operational safety. PWR cores generally utilize a symmetrical loading pattern, meaning that fuel assemblies of varying enrichment and burnup depths are arranged in a 1 / 4 or 1 / 6 symmetrical pattern to achieve a well-balanced core power distribution. By employing appropriate technical methods to assess the symmetry of the core power distribution, the reactor's operational safety and compliance with the core design can be evaluated. When some fuel assemblies cannot be loaded into the core according to the original symmetrical loading plan for some reasons, such as a nuclear fuel element seal failure in a fuel assembly, some PWR models allow asymmetric loading. This means using spare fuel assemblies to replace the fuel assemblies that cannot be loaded according to the original loading plan. Because the enrichment or fuel depth of the spare fuel assemblies will differ from that of the fuel assemblies that cannot be loaded into the core, they will present an inconsistent power distribution with other symmetrically positioned fuel assemblies in the core, causing the PWR core to exhibit asymmetric loading characteristics. Fuel assemblies that cause asymmetric loading characteristics in the core are called asymmetric assemblies. For asymmetric cores, the core power distribution cannot be completely symmetrical. Reasonable methods are needed to check that the core power and its distribution are within appropriate operating limits and conditions, which is of great significance to the operational safety of the reactor. Summary of the Invention
[0003] The purpose of the present invention is to provide a method for checking the symmetry of the power distribution of an asymmetrically loaded hexagonal core in a nuclear power plant. By checking the monitoring reliability and relative deviation of the fuel assembly power crest factor (the ratio of the power of a certain fuel assembly to the average power of the core, hereinafter referred to as Kq) in the core measurement system, and reasonably adjusting the evaluation criteria for asymmetric components, it is determined that the core power distribution has good symmetry, which can improve the safety and reliability of the operation of the nuclear power unit.
[0004] In order to achieve the above object, the technical solution adopted by the present invention is:
[0005] A method for checking the symmetry of power distribution in an asymmetrically loaded hexagonal core of a nuclear power plant:
[0006] Step 1: Confirm that the core measurement system is working properly and the neutron flux detectors arranged in the reactor are usable;
[0007] Step 2: Divide the fuel assembly loading area in the core into symmetric groups; determine the symmetry of the core power distribution by examining the relative deviation of Kq within the symmetric groups; Kq is the ratio of a fuel assembly power to the average core power;
[0008] Step 3: Select a suitable initial state, with the reactor power required to be no less than 40% of the rated power, to achieve xenon equilibrium;
[0009] Step 4: Check the reliability of Kq monitoring at the core center. When the Kq of the fuel assembly at the center meets the design boundary value requirements, the Kq monitoring at this position is considered reliable.
[0010] Step 5: Check the reliability of Kq monitoring of all symmetrically positioned fuel assemblies in a symmetrical group divided in Step 2, and confirm one by one that the Kq of the fuel assemblies at the aforementioned symmetrical positions meet the design boundary requirements. Otherwise, the Kq monitoring at the corresponding position is considered unreliable.
[0011] Step 6: Calculate the average Kq of all symmetrically positioned fuel assemblies in the symmetrical group selected in step 5;
[0012] Step 7: Calculate the deviation between the Kq of each symmetrically positioned fuel assembly in the symmetrical group selected in Step 5 and the average Kq of all symmetrically positioned fuel assemblies in the symmetrical group calculated in Step 6;
[0013] Step 8: Repeat steps 5, 6, and 7 to calculate the absolute value of the difference between the Kq of all symmetric positions in all symmetric groups and the average Kq of the symmetric groups to which they belong, to obtain the relative power deviation of the entire core;
[0014] Step 9: Check the reliability and relative deviation of Kq monitoring of the entire core and determine the symmetry of the hexagonal core power distribution.
[0015] The step 1: the neutron flux detectors arranged in the reactor need to be more than 90% available.
[0016] Step 2: Divide the fuel assemblies in the core into several symmetrical groups based on the fuel assembly type, namely, the difference in uranium 235 enrichment and the difference in the number of gadolinium-containing fuel rods.
[0017] The second step is: for the hexagonal core, the core is divided into symmetry groups according to 60° symmetry or 30° symmetry.
[0018] Step 3: A reactor with this feature will not have obvious power distortion, and the Kq at any position in the core will not be too large. Otherwise, the Kq monitoring at this position is considered unreliable, and necessary inspections and processing are required to ensure the reliability of Kq monitoring of the entire core and carry out power distribution symmetry inspections.
[0019] The fourth step: For the center position of the hexagonal core, there is no symmetrical position at this position. It is only necessary to check the Kq monitoring reliability of this position without checking the symmetry.
[0020] Step nine: The symmetry of the power distribution of the hexagonal core is determined by the following method: Kq of the entire core is less than the design boundary value at the corresponding power level; the relative power deviation of the entire core meets the evaluation standard requirements. If all the above conditions are met, it is determined that the power distribution of the asymmetrically loaded hexagonal core meets the design expectations, exhibits good symmetry, and the reactor is in a safe operating state.
[0021] Regarding the evaluation criteria for the relative deviation of Kq in a symmetric group, different evaluations should be made according to the average load of the symmetric group. For a high-load symmetric group, the neutron flux at the corresponding core position is larger, the monitoring and calculation error of the core measurement system at this position is smaller, and the Kq monitoring and calculation accuracy at this position is higher. Therefore, compared with a low-load symmetric group, the evaluation criteria for the relative deviation of Kq in a high-load symmetric group should be stricter; if a symmetric group contains asymmetric components, then when evaluating the power distribution symmetry of the asymmetric components and other components in the symmetric group, it is necessary to superimpose the asymmetry on the basis of the original symmetry evaluation criteria. The asymmetry is calculated by the core designer, and the core design software is used to calculate the theoretical calculation deviation between the power peak factor of the asymmetric component and the average power peak factor of other components in the symmetric group. By superimposing this theoretical calculation deviation on the basis of the original symmetry evaluation criteria, a reliable asymmetric component power distribution symmetry evaluation standard can be obtained.
[0022] The beneficial effects achieved by the present invention are:
[0023] In view of the particularity of the asymmetric loading method of the hexagonal core of a nuclear power plant, the present invention divides the fuel assembly loading area in the core into several symmetric groups in different symmetric ways to check the relative deviation of the power peak factor of the fuel assembly, and provides the boundary value and relative deviation evaluation standard of the fuel assembly power peak factor, and reasonably adjusts the evaluation standard of the asymmetric assembly power peak factor. This provides a method for checking the power distribution symmetry of the asymmetric loaded hexagonal core of a nuclear power plant during the power operation stage, which can assist in judging the safety status of the reactor and provide technical guarantee for the safe and stable operation of the nuclear power unit. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 This is a diagram of the layout of neutron flux detectors and adjustment rods in the hexagonal core of a nuclear power plant;
[0025] Figure 2 This is a schematic diagram of the nuclear fuel assembly loading layout for a hexagonal core of a nuclear power plant;
[0026] Figure 3is the boundary value of Kq when the hexagonal core of a nuclear power plant operates at different reactor powers. DETAILED DESCRIPTION
[0027] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
[0028] The core measurement system of a nuclear power plant can generally monitor and calculate the Kq of the entire core. Based on this function, the method provided by the present invention is used to check the symmetry of the power distribution of an asymmetrically loaded hexagonal core.
[0029] Step 1: Confirm that the core measurement system is working properly. The neutron flux detectors arranged in the reactor need to be more than 90% available.
[0030] Step 2: Divide the fuel assembly loading area within the core into symmetry groups. Generally, fuel assemblies within the core are divided into several symmetry groups based on fuel assembly type (e.g., differences in uranium-235 enrichment, differences in the number of gadolinium-containing fuel rods, etc.). For hexagonal cores, symmetry groups can generally be divided according to 60° or 30° symmetry. The symmetry of the core power distribution can be determined by examining the relative deviation of Kq within the symmetry group.
[0031] Step 3: Select an appropriate initial state, with the reactor power requirement being no less than 40% of rated power to achieve xenon equilibrium. The reactor of the target nuclear power unit must be operating at a relatively high power level and in xenon equilibrium to exhibit a distinct and stable power distribution. Reactors with these characteristics will exhibit no significant power distortion, and the Kq value at any location within the core will not be excessively large. If this is not the case, Kq monitoring at that location is considered unreliable and requires necessary inspection and action. To ensure the reliability of Kq monitoring throughout the entire core, a power distribution symmetry check should be conducted.
[0032] Step 4: Check the reliability of Kq monitoring at the core center. When the Kq of the fuel assembly at the center meets the design boundary value requirements, Kq monitoring at this location is considered reliable. For the center of a hexagonal core, since there is no symmetry at this location, only the reliability of Kq monitoring at this location needs to be checked, without checking symmetry.
[0033] Step 5: Check the reliability of Kq monitoring for all symmetrically located fuel assemblies within a symmetrical group identified in Step 2. Confirm that the Kq of each symmetrically located fuel assembly meets the design boundary requirements. Otherwise, the Kq monitoring at the corresponding location is considered unreliable.
[0034] Step 6: Calculate the average Kq of all symmetrically positioned fuel assemblies in the symmetrical group selected in Step 5.
[0035] Step 7: Calculate the deviation between the Kq of each symmetrically positioned fuel assembly in the symmetrical group selected in Step 5 and the average Kq of all symmetrically positioned fuel assemblies in the symmetrical group calculated in Step 6.
[0036] Step 8: Repeat steps 5, 6, and 7 to calculate the absolute value of the difference between the Kq of all symmetric positions in all symmetric groups and the average Kq of the symmetric groups to which they belong, and obtain the relative power deviation of the entire core.
[0037] Step 9: Check the reliability and relative deviation of Kq monitoring of the entire core, and use the following method to determine the symmetry of the hexagonal core power distribution.
[0038] 1) The Kq of the entire core is less than the design boundary value at the corresponding power level;
[0039] 2) The relative power deviation of the entire core meets the evaluation standard requirements. The evaluation standard for the relative deviation of Kq in the symmetry group should be evaluated differently according to the average load of the symmetry group. For the high-load symmetry group, since the neutron flux at the corresponding core position is larger, the monitoring and calculation error of the core measurement system at this position is smaller, and the Kq monitoring and calculation accuracy at this position is higher. Therefore, compared with the low-load symmetry group, the evaluation standard for the relative deviation of Kq in the high-load symmetry group should be stricter. If a symmetry group contains asymmetric components, when evaluating the power distribution symmetry of the asymmetric components and other components in the symmetry group, it is necessary to superimpose the asymmetry on the basis of the original symmetry evaluation standard. The asymmetry is generally calculated by the core designer. The core design software is used to calculate the theoretical calculation deviation of the power peak factor of the asymmetric component and the average power peak factor of other components in the symmetry group. By superimposing this theoretical calculation deviation on the basis of the original symmetry evaluation standard, a reliable asymmetric component power distribution symmetry evaluation standard can be obtained.
[0040] If the above conditions 1) and 2) are met, it can be judged that the power distribution of the asymmetric loaded hexagonal core meets the design expectations, shows good symmetry, and the reactor is in a safe operating state.
[0041] Taking a hexagonal core unit of a nuclear power plant as an example, the method provided by the present invention is described in detail. The specific implementation method is as follows:
[0042] Step 1: Verify that the core measurement system is functioning properly. The neutron flux detectors deployed in the reactor must be at least 90% operational. In this case, the reactor has 54 x 7 neutron flux detectors (54 groups, each with 7 detectors evenly spaced along the height of the fuel assembly). Therefore, at least 341 neutron flux detectors must be operational.
[0043] Step 2: Divide the fuel assembly loading areas in the core into symmetric groups. In this case, the 163 fuel assembly loading areas in the core are divided into symmetric groups. For a hexagonal core, the groups can generally be divided according to 60° symmetry. That is, the core is divided into 6 sectors, and a position is symmetrically selected in each sector as a symmetric group, totaling 28 groups, as shown in Table 1.
[0044] Table 1 The hexagonal core of a nuclear power plant is divided into symmetry groups based on 60° symmetry
[0045]
[0046]
[0047] When only the main regulating rod group is inserted into the core, the 28 60° symmetric groups can be further integrated, that is, divided into groups with 30° symmetry. The symmetry of different types of nuclear fuel assemblies relative to the main regulating rod bundle needs to be considered. Figure 2 Taking the core loading shown in FIG2 as an example, it can be divided into 19 30° symmetry groups, as shown in Table 2.
[0048] Table 2 The hexagonal core of a nuclear power plant is divided into symmetry groups based on 30° symmetry
[0049]
[0050]
[0051] When the regulating rod group other than the main regulating rod group is inserted into the core, the symmetry check can be performed by dividing the rods into groups with 60° symmetry. When only the main regulating rod group is inserted into the core, the symmetry check can be performed by dividing the rods into groups with 30° symmetry. This can expand the comparison range of some core areas and thus improve the reliability of the symmetry check. Figure 1 shown.
[0052] Step 3: Select an appropriate initial state. The reactor power must be at least 40% of rated power to achieve xenon equilibrium. In this case, the reactor power is 100% of rated power, and only the main regulating rod assembly is inserted into the core.
[0053] Step 4: Check the reliability of Kq monitoring of the only 08-29 position in the first symmetric group. Figure 3 The Kq monitoring at positions 08-29 is considered reliable when the power-dependent boundary values are shown. In this case, the reactor power is 100% rated power. The Kq at any position in the core should be less than 1.35; otherwise, the Kq monitoring at the corresponding position is considered unreliable.
[0054] Step 5: Check the reliability of Kq monitoring at the six symmetrical positions in the second symmetrical group (08-31, 09-30, 09-28, 08-27, 07-28, and 07-30). Confirm that Kq at each of the six symmetrical positions is less than 1.35; otherwise, the Kq monitoring at the corresponding position is considered unreliable.
[0055] Step 6: Calculate the average value aveKq2 of Kq of all 6 symmetric positions in the second symmetry group. The calculation method of aveKq2 is
[0056] In the formula, aveKq i is the average value of Kq of all symmetric positions in the i-th symmetry group (if the i-th symmetry group contains asymmetric components, then aveKq i is the average value of the remaining components Kq after removing the asymmetric component Kq in the i-th symmetric group), Kq ij is the Kq of the jth symmetric position in the i-th symmetry group; n is the total number of symmetric positions in the symmetry group.
[0057] Step 7: Calculate Kq of the first symmetric position 08-31 in the second symmetric group 21 The deviation ΔKq from aveKq2 of the symmetry group 21 , ΔKq 21 The calculation method is △Kq ij =|Kq ij -aveKq i |, calculate Kq of all symmetric positions in the second symmetry group in turn 2j The deviation ΔKq from aveKq2 of the symmetry group 2j .
[0058] Step 8: Repeat steps 5, 6, and 7 to calculate Kq for all symmetric positions in all symmetric groups. ij and aveKq of the symmetry group to which it belongs i The absolute value of the difference between the two is used to obtain the relative power deviation of the whole core ΔKq ij .
[0059] Step 9: Check the reliability and relative deviation of Kq monitoring of the entire core, and use the following method to determine the symmetry of the hexagonal core power distribution.
[0060] 1) The Kq of the entire core is less than the boundary value at the corresponding power level;
[0061] 2) ΔKq of the entire core ij≤△. When aveKq of the symmetric group to which a certain symmetrical position in the core belongs is greater than 1.1, the corresponding △ is 0.1; when aveKq of the symmetric group to which a certain symmetrical position in the core belongs is less than or equal to 1.1, the corresponding △ is 0.25. For the evaluation of asymmetric components, the asymmetry u must be superimposed on the aforementioned △ value standard, that is, when aveKq of the symmetric group to which an asymmetric component belongs is greater than 1.1, the corresponding △ of the asymmetric component is evaluated as 0.1+u; when aveKq of the symmetric group to which an asymmetric component belongs is less than or equal to 1.1, the corresponding △ of the asymmetric component is evaluated as 0.25+u. The calculation method of asymmetry is u=|Kq i′j′ -aveKq i′ |, where aveKq i′ is the average value of Kq calculated at the jth symmetric position (excluding asymmetric component positions) in the i-th symmetry group using the core design software, Kq i′j′ is the calculated value of Kq for the asymmetric component position calculated using the core design software.
[0062] If the above conditions 1) and 2) are met, it can be judged that the power distribution of the asymmetric loaded hexagonal core meets the design expectations, shows good symmetry, and the reactor is in a safe operating state.
Claims
1. A method for checking the symmetry of power distribution in an asymmetrically loaded hexagonal core of a nuclear power plant, characterized by: The following steps are involved: Step 1: Confirm that the core measurement system is working properly and the neutron flux detectors arranged in the reactor are usable; Step 2: Divide the fuel assembly loading area in the core into symmetric groups; determine the symmetry of the core power distribution by examining the relative deviation of Kq within the symmetric groups; Kq is the ratio of a fuel assembly power to the average core power; Step 3: Select a suitable initial state, with the reactor power required to be no less than 40% of the rated power, to achieve xenon equilibrium; Step 4: Check the reliability of Kq monitoring at the core center. When the Kq of the fuel assembly at the center meets the design boundary value requirements, the Kq monitoring at this position is considered reliable. Step 5: Check the reliability of Kq monitoring of all symmetrically positioned fuel assemblies in a symmetrical group divided in Step 2, and confirm one by one that the Kq of the fuel assemblies at the aforementioned symmetrical positions meet the design boundary requirements. Otherwise, the Kq monitoring at the corresponding position is considered unreliable. Step 6: Calculate the average Kq of all symmetrically positioned fuel assemblies in the symmetrical group selected in step 5; Step 7: Calculate the deviation between the Kq of each symmetrically positioned fuel assembly in the symmetrical group selected in Step 5 and the average Kq of all symmetrically positioned fuel assemblies in the symmetrical group calculated in Step 6; Step 8: Repeat steps 5, 6, and 7 to calculate the absolute value of the difference between the Kq of all symmetric positions in all symmetric groups and the average Kq of the symmetric groups to which they belong, to obtain the relative power deviation of the entire core; Step 9: Check the reliability and relative deviation of Kq monitoring of the entire core and determine the symmetry of the hexagonal core power distribution.
2. The method for checking the symmetry of power distribution in an asymmetrically loaded hexagonal core of a nuclear power plant according to claim 1, characterized in that: Step 1: The neutron flux detectors arranged in the reactor need to be more than 90% available.
3. The method for checking the symmetry of power distribution in an asymmetrically loaded hexagonal core of a nuclear power plant according to claim 1, characterized in that: Step 2: Divide the fuel assemblies in the core into several symmetrical groups based on the fuel assembly type, the difference in uranium-235 enrichment, and the difference in the number of gadolinium-containing fuel rods.
4. The method for checking the symmetry of power distribution in a hexagonal core with asymmetrical loading in a nuclear power plant according to claim 3, characterized in that: Step 2: For hexagonal cores, divide the cores into symmetry groups according to 60° symmetry or 30° symmetry.
5. The method for checking the symmetry of power distribution in an asymmetrically loaded hexagonal core of a nuclear power plant according to claim 1, characterized in that: Step 3: A reactor with this feature will not have obvious power distortion, and the Kq at any position in the core will not be too large. Otherwise, the Kq monitoring at that position is considered unreliable, and necessary inspections and processing are required to ensure the reliability of Kq monitoring of the entire core and carry out power distribution symmetry inspections.
6. The method for checking the symmetry of power distribution in an asymmetrically loaded hexagonal core of a nuclear power plant according to claim 1, characterized in that: Step 4: For the center position of the hexagonal core, there is no symmetrical position at this position. It is only necessary to check the Kq monitoring reliability of this position without checking the symmetry.
7. The method for checking the symmetry of power distribution in an asymmetrically loaded hexagonal core of a nuclear power plant according to claim 1, characterized in that: Step 9: Use the following method to determine the symmetry of the hexagonal core power distribution: the Kq of the entire core is less than the design boundary value at the corresponding power level; the relative power deviation of the entire core meets the evaluation standard requirements. If all the above conditions are met, it is determined that the power distribution of the asymmetric hexagonal core meets the design expectations, shows good symmetry, and the reactor is in a safe operating state.
8. The method for checking the symmetry of power distribution in an asymmetrically loaded hexagonal core of a nuclear power plant according to claim 7, characterized in that: Regarding the evaluation criteria for the relative deviation of Kq in a symmetric group, different evaluations should be made according to the average load of the symmetric group. For a high-load symmetric group, the neutron flux at the corresponding core position is larger, the monitoring and calculation error of the core measurement system at this position is smaller, and the Kq monitoring and calculation accuracy at this position is higher. Therefore, compared with a low-load symmetric group, the evaluation criteria for the relative deviation of Kq in a high-load symmetric group should be stricter; if a symmetric group contains asymmetric components, then when evaluating the power distribution symmetry of the asymmetric components and other components in the symmetric group, it is necessary to superimpose the asymmetry on the basis of the original symmetry evaluation criteria. The asymmetry is calculated by the core designer, and the core design software is used to calculate the theoretical calculation deviation between the power peak factor of the asymmetric component and the average power peak factor of other components in the symmetric group. By superimposing this theoretical calculation deviation on the basis of the original symmetry evaluation criteria, a reliable asymmetric component power distribution symmetry evaluation standard can be obtained.