A method for evaluating reactor core quadrant power tilt state

Abstract

The present invention relates to a method for evaluating the quadrant power tilt state of a reactor core, comprising the following steps: S1, obtaining the position information and deformation data corresponding to each fuel assembly of the previous cycle core; S2, obtaining the displacement of the fuel assembly in the core based on the deformation data of the fuel assembly; S3, correcting the modeling model corresponding to the current cycle core based on the displacement of the fuel assembly and the position information of the fuel assembly, so as to obtain the core power tilt data corresponding to the reactor according to the corrected modeling model; S4, obtaining the evaluation result of the core power tilt state according to the core power tilt data. The implementation of the present invention can derive the quadrant power tilt state of a nuclear power reactor during operation by simple means, so as to further ensure the operation safety of the core.

Description

Technical Field

[0001] The present invention relates to the field of nuclear power technology, and more specifically to a method for evaluating a reactor core quadrant power tilt state. Background Art

[0002] Core quadrant power tilt refers to the asymmetry of power levels in each quadrant of the core, with some areas being higher; its essence is that there is a systematic and regional deviation between the theoretical calculated power and the actual core power. The reasons for this phenomenon are numerous and complex. It is difficult to capture the power tilt state of the core before the core is started; only by conducting flux diagram experimental measurements during the operation of the core can its power tilt state be discovered. Once the core scheme is determined, the power tilt state will not be able to be effectively controlled after the core is started. Once the value exceeds the limit, it will restrict the safety and economy of the core operation. Therefore, the control of power tilt mainly depends on the scheme design in the refueling design stage.

[0003] In the prior art, the consideration of power tilt in the refueling design stage is mainly based on historical experience, through conscious and qualitative evaluation of possible power tilt states, and through the adjustment of the core loading plan, deliberately suppressing this possible trend. The above process is mainly based on personal experience, with a large impact of human factors, and lacks effective means of quantitative evaluation. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for evaluating the quadrant power tilt state of a reactor core in view of the above-mentioned technical defects of the prior art.

[0005] The technical solution adopted by the present invention to solve the technical problem is: constructing a method for evaluating the quadrant power tilt state of a reactor core, comprising the following steps:

[0006] S1, obtaining the position information and deformation data corresponding to each fuel assembly in the core of the previous cycle;

[0007] S2. acquiring the displacement of the fuel assembly in the core based on the deformation data of the fuel assembly;

[0008] S3, based on the displacement of the fuel assembly and the position information of the fuel assembly, correcting the modeling model corresponding to the core of the current cycle, so as to obtain the core power tilt data corresponding to the reactor according to the corrected modeling model;

[0009] S4. Obtaining an evaluation result of a core power tilt state according to the core power tilt data.

[0010] Preferably, in the reactor core quadrant power tilt state evaluation method of the present invention, in the step S1, the step of obtaining the position information and deformation data corresponding to each fuel assembly in the core of the previous cycle comprises:

[0011] During the refueling overhaul process of a nuclear power unit, the position information of each fuel assembly in the core and the deformation data of the fuel assembly in the previous cycle are obtained.

[0012] Preferably, in the reactor core quadrant power tilt state evaluation method of the present invention, it also includes:

[0013] The inherent deformation characteristics corresponding to each position in the core are obtained, so as to obtain the deformation data of the fuel assembly in the previous cycle according to the position information of the fuel assembly in the previous cycle and the inherent deformation characteristics corresponding to the position.

[0014] Preferably, in the reactor core quadrant power tilt state evaluation method of the present invention, it also includes:

[0015] The inherent deformation characteristics are obtained based on historical data during the overhaul of the nuclear power unit, wherein the historical data includes position information of each fuel assembly in the core and deformation data of the fuel assembly obtained during each refueling overhaul of the nuclear power unit.

[0016] Preferably, in the reactor core quadrant power tilt state evaluation method of the present invention, in the step S2, the displacement of the fuel assembly corresponding to the core is obtained based on the deformation data of the fuel assembly; comprising:

[0017] The deformation data of the fuel assembly is converted based on a preset conversion function to obtain a displacement of the fuel assembly relative to a preset position.

[0018] Preferably, in the reactor core quadrant power tilt state evaluation method described in the present invention, the preset conversion function is: F2=F1 / K, wherein F1 is the deformation data of the fuel assembly, F2 is the displacement of the fuel assembly, and K is a constant.

[0019] Preferably, in the reactor core quadrant power tilt state evaluation method of the present invention, in the step S3, the modeling model corresponding to the core of the current cycle is corrected based on the displacement of the fuel assembly and the position information of the fuel assembly, so as to obtain the core power tilt data corresponding to the reactor according to the corrected modeling model; comprising:

[0020] Based on the displacement of the fuel assembly and the position information of the fuel assembly, the gap between the fuel assemblies in the core of the current cycle is reset to update the modeling model corresponding to the core according to the new gap to obtain the core power tilt data.

[0021] Preferably, in the reactor core quadrant power tilt state evaluation method of the present invention, in step S4, obtaining the evaluation result of the core power tilt state according to the core power tilt data includes:

[0022] It is determined whether the core power tilt data is greater than a preset value, and when the core power tilt data is less than the preset value, it is determined that the core power tilt state is reasonable, otherwise it is determined that the core power tilt state is unreasonable.

[0023] Preferably, in the reactor core quadrant power tilt state evaluation method of the present invention, it also includes:

[0024] When it is determined that the core power tilt state is unreasonable, the power change state of the fuel assembly is obtained to adjust the position of the fuel assembly according to the power change state of the fuel assembly.

[0025] Preferably, in the reactor core quadrant power tilt state evaluation method of the present invention, it also includes:

[0026] When the power change state of the fuel assembly is increasing, the power change state of the fuel assembly at the symmetrical position corresponding to the fuel assembly is obtained, and the fuel assembly with a smaller power level is obtained for replacement;

[0027] When the power change state of the fuel assembly is decreasing, the power change state of the fuel assembly at the symmetrical position corresponding to the fuel assembly is obtained, and the fuel assembly with a larger power level is obtained for replacement.

[0028] The implementation of the reactor core quadrant power tilt state evaluation method of the present invention has the following beneficial effects: the quadrant power tilt state during operation of the nuclear power reactor can be derived by simple means to further ensure the safety of the core operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0030] Figure 1 It is a structural schematic diagram of a reactor core quadrant power tilt state evaluation method of the present invention;

[0031] Figure 2 It is a schematic diagram of the change of core gap;

[0032] Figure 3 is a schematic diagram of a first embodiment of a core layout;

[0033] Figure 4 is a schematic diagram of fuel assembly deformation;

[0034] Figure 5 It is a schematic diagram of power distribution of a normal core;

[0035] Figure 6 It is a schematic diagram of the power distribution of the core caused by the deformation of the fuel assembly;

[0036] Figure 7 It is a schematic diagram of the degree of power change of the core caused by the deformation of the fuel assembly;

[0037] Figure 8 This is a schematic diagram of the fuel assembly position adjustment process. DETAILED DESCRIPTION

[0038] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0039] like Figure 1 As shown, in a first embodiment of a reactor core quadrant power tilt state evaluation method of the present invention, the following steps are included: S1, obtaining the position information and deformation data corresponding to each fuel assembly in the core of the previous cycle. Specifically, in a reactor, the fuel assembly generally has a fixed installation position in the core. In the reactor, the reactor power distribution will meet the requirements according to the inherent design. However, during operation, the fuel assembly will be deformed due to various reasons, and the deformation of the fuel assembly will usually affect the power distribution of the core. That is, in each cycle, the deformation data of the core will affect the next cycle. Therefore, it is necessary to analyze the next cycle based on the deformation data of the previous cycle. Among them, the fuel assemblies at different positions have different power distributions in the reactor, and the deformation of the fuel assemblies has different effects on the power distribution of the entire reactor. Therefore, it is necessary to obtain the deformation data of the fuel assemblies at different positions for analysis. That is, it can be understood that it is necessary to simultaneously obtain the position information of the fuel assembly and the deformation data corresponding to the fuel assembly.

[0040] In one embodiment, in the step S1, the position information and deformation data corresponding to each fuel assembly in the core of the previous cycle are obtained; including: in the process of refueling overhaul of the nuclear power unit, the position information of each fuel assembly in the core of the previous cycle and the deformation data of the fuel assembly are obtained. That is, in the process of refueling overhaul of the nuclear power plant, all fuel assemblies can be unloaded and hoisted to a specific area, and the deformation measurement of the fuel assemblies can be carried out to obtain the deformation of each fuel assembly at different grid heights. Among them, the deformation measurement method of the fuel assembly can adopt currently common methods such as ultrasound and laser photography. In some embodiments, only the deformation data of a specific position of the fuel assembly can be obtained, for example, the deformation data of the 8-layer grid position of the fuel assembly can be obtained. That is, a fuel assembly is very high, and the deformation is inconsistent at different heights. Common fuel assemblies (such as those used in CPR1000 reactors) have 8 positioning grids on the axial height. When measuring, the measurement can be carried out at these 8 positions.

[0041] In one embodiment, the inherent deformation characteristics corresponding to each position in the core can also be obtained, so as to obtain the deformation data of the fuel assembly in the previous cycle according to the position information of the fuel assembly and the inherent deformation characteristics corresponding to the position. That is, in the reactor environment, the deformation of the fuel assembly at each position often has a certain inherent deformation trend, and for each position, the deformation measurement results of multiple cycles can be used as the inherent deformation distribution of the unit. That is, the inherent deformation characteristics of each position in the unit core are obtained. Based on the inherent deformation characteristics corresponding to the position, the deformation data of the fuel assembly at the position can be obtained. Finally, it can be understood that according to the position information of each fuel assembly in the core, the deformation data of the fuel assembly obtained during the previous cycle can be derived. It can be understood here that the deformation data is the data of the fuel assembly after the optimization of the core relative to the previous time. For example, it can be used to obtain the deformation caused by one cycle.

[0042] Optionally, in the reactor core quadrant power tilt state evaluation method of the present invention, the inherent deformation characteristics can be obtained based on historical data during the overhaul of the nuclear power unit, wherein the historical data includes the position information of each fuel assembly in the core and the deformation data of the fuel assembly obtained during each refueling overhaul of the nuclear power unit. That is, a measurement can be carried out at each refueling overhaul stage, and the deformation conditions at each position, i.e., the data of the past years, can be processed, for example, the average value can be taken as the inherent deformation characteristics of the unit. There is no need to take the average value for the first measurement, and the average value can be taken after multiple measurements.

[0043] S2. Obtain the displacement of the fuel assembly in the core based on the deformation data of the fuel assembly. Specifically, if the fuel assembly is deformed, its position in the core will move. At this time, the displacement of the fuel assembly in the core can be obtained based on the deformation data of the fuel assembly. In the process of displacement calculation, the XY direction (i.e., the horizontal direction) can be considered independently, and the deformation of the entire fuel assembly can be decomposed into displacements in the X and Y directions. In the axial direction (i.e., the z direction), according to the grid height segmentation, the grid at the same grid height adopts the deformation at this grid. The deformation will eventually affect the position of the fuel assembly in the core, and then the displacement of the fuel assembly in the core can be obtained based on the deformation.

[0044] Optionally, in step S2, the displacement of the fuel assembly in the core corresponding to the fuel assembly is obtained based on the deformation data of the fuel assembly; including: converting the deformation data of the fuel assembly based on a preset conversion function to obtain the displacement of the fuel assembly relative to a preset position. Among them, the displacement caused by the deformation of the fuel assembly has a specific rule, so the deformation data of the fuel assembly can be converted based on the preset conversion function to obtain the corresponding displacement. For example, the core has 157 positions for arranging components, and the center of each position is theoretically fixed; but in fact, due to the deformation of the fuel assembly, its center position will be offset, which corresponds to the displacement. Among them, the preset conversion function is: F2 = F1 / K, where F1 is the deformation data of the fuel assembly, F2 is the displacement of the fuel assembly, and K is a constant. In one embodiment, the value of K can be 1.4, and the value can also be adjusted according to different actual scenarios.

[0045] S3. Based on the displacement of the fuel assembly and the position information of the fuel assembly, the modeling model corresponding to the core in the current cycle is corrected to obtain the core power tilt data corresponding to the reactor according to the corrected modeling model. That is, after the fuel assembly is deformed, the parameters of the fuel assembly will also change, for example, the gap between the fuel assembly and the fuel assembly at different heights will change. The power distribution of the core will also change relative to the previous design value. In the new cycle process, the new core power distribution calculation process needs to be calculated based on new parameters such as gap data, that is, the gap between the fuel assembly and the fuel assembly in the core calculation model is adjusted accordingly to obtain the latest core power distribution. The new cycle can be understood as a cycle to be performed. In the new cycle, the gap between each fuel assembly in the core can be reset based on the displacement of the fuel assembly and the position information of the fuel assembly, so as to update the modeling model corresponding to the core according to the new gap to obtain the core power tilt data. The specific process is that in the core modeling process, the gap between the positions of each fuel assembly is reset. Changes in the gap between fuel assemblies will affect the local moderation conditions, thus causing changes in the core power distribution; when the deformation distribution of the fuel assemblies is distributed in a certain direction, quadrant power tilt will occur. It can be understood that this calculation process is a theoretical calculation process, which is equivalent to a prediction process. Ultimately, it is beneficial that the measurement data is based on the old cycle; the core model used for theoretical calculation is a model for the new cycle to predict the quadrant power tilt.

[0046] In a specific embodiment, if Figure 2 As shown, there are four fuel assemblies, 1, 2, 3, and 4, and their deformation measurement results are converted into the displacement of the fuel assembly in the stack. Assuming that the initial gap width between assembly 1 and assembly 2 is 2 mm, when assembly 1 deforms to the right (X+ direction) by 1.4 mm and displaces by 1 mm; while assembly 2 does not deform in the X direction and has a displacement of 0 mm; then the gap width between assembly 1 and assembly 2 is d = 2-1 + 0 = 1 (mm), and finally the core power distribution calculation needs to be performed based on the new gap.

[0047] S4. Obtain an evaluation result of the core power tilt state according to the core power tilt data. Specifically, finally obtain an evaluation result of the core power tilt state according to the core power tilt data. In one embodiment, it can be judged whether the core power tilt data is greater than a preset value, and when the core power tilt data is less than the preset value, the core power tilt state is judged to be reasonable, otherwise the core power tilt state is judged to be unreasonable. That is, it can be judged whether the current core tilt state is within an acceptable range according to the size of the core power tilt data. For example, if the current power tilt is less than 1%, the power tilt state of the current scheme is reasonable and acceptable. If the current power tilt is greater than 1%, the power tilt state of the current scheme is unreasonable and cannot be accepted.

[0048] Optionally, in the reactor core quadrant power tilt state evaluation method of the present invention, it also includes, when it is determined that the core power tilt state is unreasonable, obtaining the power change state of the fuel assembly to adjust the position of the fuel assembly according to the power change state of the fuel assembly. That is, when it is determined that the current core power tilt state is unreasonable, that is, the current core power arrangement is not ideal, the position of the fuel assembly can be adjusted at this time to make the power distribution of the core a more ideal state. Among them, the position adjustment method of the fuel assembly can be confirmed according to the power change state of the fuel assembly.

[0049] In one embodiment, when the power change state of the fuel assembly is increasing, the power change state of the fuel assembly at the symmetrical position corresponding to the fuel assembly is obtained, and the fuel assembly with a smaller power level is obtained for replacement. That is, when the power of the current fuel assembly at this position increases due to deformation, the fuel assembly at this position can be replaced with the fuel assembly at the symmetrical position with a smaller power level.

[0050] In one embodiment, when the power change state of the fuel assembly is decreasing, the power change state of the fuel assembly at the symmetrical position corresponding to the fuel assembly is obtained, and the fuel assembly with a larger power level is obtained for replacement. That is, when the power of the current fuel assembly at this position decreases due to deformation, the fuel assembly at this position can be replaced with the fuel assembly at the symmetrical position with a larger power level.

[0051] In a specific embodiment, Figure 3 As shown in the figure, there are 157 fuel assemblies in the core (one square represents one assembly); there is a certain gap between the fuel assemblies during the actual loading process. Conventional theoretical calculations do not take into account the deformation and offset of the actual fuel assemblies in the core. That is, the spacing between the fuel assemblies, up and down, left and right, are all nominal values ​​(specific / fixed values). Figure 4The figure shows the schematic structure of a fuel assembly. When the fuel assembly undergoes bending deformation (viewed axially), in a two-dimensional model, it is manifested as the fuel assembly shifting to the right with inconsistent deformation amounts at different heights. When applied to a two-dimensional model, generally the overall average value is taken. If the fuel assembly is deformed, its position within the reactor core will shift. As Figure 2 shown, the spacing between fuel assemblies changes.

[0052] For a given reactor core loading scheme, as Figure 5 shown, calculate the power distribution levels of each component in the reactor core when the fuel assembly gap distribution remains unchanged, Pa(i = 1,..., n); (where the typical value of n is 157, that is, 157 fuel assemblies). As Figure 6 shown, calculate the power distribution levels of each fuel assembly when considering the asymmetric fuel assembly gap distribution, Pb(i = 1,..., n). Obtain the calculation deviation between the two models as Figure 7 shown. Compare the magnitudes of Pa and Pb for each fuel assembly one by one. If Pa > Pb, it proves that the power at this position is low, and the fuel assemblies at the symmetric position should be appropriately swapped, placing the symmetric fuel assembly with high reactivity at this position; if Pa < Pb, it proves that the power at this position is low, and the fuel assemblies at the symmetric position should be appropriately swapped, placing the symmetric fuel assembly with low reactivity at this position. As Figure 8 shown, the adjustment process can be to swap the fuel assemblies at positions a, b, c, and d as needed.

[0053] During the above process, make appropriate adjustments in combination with the overall power tilt amplitude; if there are no suitable fuel assemblies for swapping, then do not change. The reactor core loading is generally quarter-rotation symmetric, and some positions are octant symmetric; due to certain non-uniformities during the burnup process of the early cycles, there are differences in the remaining enrichments between the fuel assemblies at each symmetric position, and there are also differences in their reactivity; by swapping high-reactivity and low-reactivity fuel assemblies at symmetric positions, it is possible to effectively suppress the quadrant power tilt state during the actual operation of the reactor core.

[0054] In the present invention, based on the deformation measurement data of old fuel assemblies, during the refueling design process, the quadrant power tilt state of a nuclear power reactor during operation can be preliminarily evaluated. It is also possible to quantitatively adjust and optimize the design scheme according to the obtained evaluation index to reduce the power tilt state. Reduce the degree of reactor core quadrant tilt and further ensure the safety of the reactor core.

[0055] It can be understood that the above embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the patent scope of the present invention. It should be pointed out that, for ordinary technicians in this field, the above technical features can be freely combined without departing from the concept of the present invention, and several deformations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should belong to the coverage of the claims of the present invention.

Claims

1. A method for evaluating the quadrant power tilt state of a reactor core, characterized in that: The following steps are involved: S1, obtaining the position information and deformation data corresponding to each fuel assembly in the core of the previous cycle; S2. acquiring the displacement of the fuel assembly in the core based on the deformation data of the fuel assembly; S3, based on the displacement of the fuel assembly and the position information of the fuel assembly, correcting the modeling model corresponding to the core of the current cycle, so as to obtain the core power tilt data corresponding to the reactor of the current cycle according to the corrected modeling model; S4. obtaining an evaluation result of a core power tilt state according to the core power tilt data; In the step S2, the displacement of the fuel assembly in the core is obtained based on the deformation data of the fuel assembly; including: Converting the deformation data of the fuel assembly based on a preset conversion function to obtain a displacement of the fuel assembly relative to a preset position; The preset conversion function is: F2= F1 / K, where F1 is the deformation data of the fuel assembly, F2 is the displacement of the fuel assembly, K is a constant, and in the process of calculating the displacement, the deformation of the fuel assembly is decomposed into displacements in the X and Y directions.

2. The reactor core quadrant power tilt state evaluation method according to claim 1, characterized in that: In the step S1, the step of obtaining the position information and deformation data corresponding to each fuel assembly in the core of the previous cycle includes: During the refueling overhaul process of a nuclear power unit, the position information of each fuel assembly in the core and the deformation data of the fuel assembly in the previous cycle are obtained.

3. The reactor core quadrant power tilt state evaluation method according to claim 1, characterized in that: The method further comprises: The inherent deformation characteristics corresponding to each position in the core are obtained, so as to obtain the deformation data of the fuel assembly in the previous cycle according to the position information of the fuel assembly in the previous cycle and the inherent deformation characteristics corresponding to the position.

4. The reactor core quadrant power tilt state evaluation method according to claim 3, characterized in that: The method further comprises: The inherent deformation characteristics are obtained based on historical data during the overhaul of the nuclear power unit, wherein the historical data includes position information of each fuel assembly in the core and deformation data of the fuel assembly obtained during each refueling overhaul of the nuclear power unit.

5. The reactor core quadrant power tilt state evaluation method according to claim 1, characterized in that: In the step S3, the modeling model corresponding to the core of the current cycle is corrected based on the displacement of the fuel assembly and the position information of the fuel assembly, so as to obtain the core power tilt data corresponding to the reactor according to the corrected modeling model; including: Based on the displacement of the fuel assembly and the position information of the fuel assembly, the gap between the fuel assemblies in the core of the current cycle is reset to update the modeling model corresponding to the core according to the new gap to obtain the core power tilt data.

6. The reactor core quadrant power tilt state evaluation method according to claim 1, characterized in that: In the step S4, obtaining the evaluation result of the core power tilt state according to the core power tilt data includes: It is determined whether the core power tilt data is greater than a preset value, and when the core power tilt data is less than the preset value, it is determined that the core power tilt state is reasonable, otherwise it is determined that the core power tilt state is unreasonable.

7. The reactor core quadrant power tilt state evaluation method according to claim 6, characterized in that: The method further comprises: When it is determined that the core power tilt state is unreasonable, the power change state of the fuel assembly is acquired to adjust the position of the fuel assembly according to the power change state of the fuel assembly.

8. The reactor core quadrant power tilt state evaluation method according to claim 7, characterized in that: The method further comprises: When the power change state of the fuel assembly is increasing, the power change state of the fuel assembly at the symmetrical position corresponding to the fuel assembly is obtained, and the fuel assembly with a smaller power level is obtained for replacement; When the power change state of the fuel assembly is decreasing, the power change state of the fuel assembly at the symmetrical position corresponding to the fuel assembly is obtained, and the fuel assembly with a larger power level is obtained for replacement.

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