System and method for replacement operation of control rod assemblies

Abstract

A method for replacement operation of control rod assemblies, according to one embodiment of the present invention, comprises the steps of: calculating a minimum degree of burnup of control rod assemblies required per cycle for each bank of a nuclear reactor based on an operation DB of a nuclear power plant; determining and classifying, as control rod assemblies to be disposed, control rod assemblies if the degree of burnup thereof is less than the product of the minimum degree of burnup and a margin of a set value; determining and classifying, as replaceable spare control rod assemblies, control rod assemblies having a degree of burnup greater than or equal to a difference between 100% and the minimum degree of burnup; determining and classifying, as control rod assemblies to be replaced, control rod assemblies having a degree of burnup that is less than the difference between 100% and the minimum degree of burnup and greater than or equal to a predetermined multiple of the product of the minimum degree of burnup and the margin of the set value; replacing, with the spare control rod assemblies, the control rod assemblies to be replaced; and managing, as history for an N+1 cycle, the remaining control rod assemblies from among the control rod assemblies to be replaced.

Description

Control rod assembly replacement operation system and method

[0001] The present invention relates to a method for operating a control rod assembly replacement, and more specifically, to a control rod assembly replacement operating system and method capable of extending the lifespan of a control rod assembly.

[0002] The reactor core output and power distribution of a nuclear power plant are primarily controlled by control rods (assemblies).

[0003] As shown in Fig. 1, the nuclear fuel assembly and control rod assembly are configured in a quadrant-symmetric form, and each control rod assembly is controlled in bank units.

[0004] Each control rod assembly can perform different functions, such as power output, power distribution, and reactor shutdown, depending on the group of control rod assemblies; therefore, their performance (absorber material, assembly composition) is configured differently.

[0005] For example, the neutron absorption capacity can be different using full-forced control rods (FSCEA) and partial-forced control rods (PSCEA), or the number of control rods per control rod assembly (12, 4, etc.) can be different.

[0006] As shown in Figure 2, in the case of current operating nuclear power plants, the insertion depth limit is set so that the insertion overlaps by a certain length for each bank. Therefore, in the case of the bank inserted first, such as Bank #5, which is the leading control group, there is a problem in that combustion proceeds rapidly and the replacement cycle is shortened.

[0007] Generally, the concept of 'life' for control rods is defined based on the burnup of the internal material, and the rods are replaced according to that burnup; additionally, the decision to replace the rods is made by evaluating their structural integrity.

[0008] However, as the demand for load-following operation methods for nuclear power plants has recently increased, the frequency of control rod usage is expected to rise. Consequently, differences in burnup between reactors and banks may increase, and this difference may be particularly significant in cases where a large number of control rods are used, such as in SMRs, making measures to improve control rod lifespan even more important.

[0009] The present invention aims to solve the problem that, as the frequency of control rod usage increases due to load-following operation, the burnout of a specific bank becomes greater, which can lead to significant differences in burnout between groups of assemblies and inevitably result in differences in structural integrity for each bank. The objective of the present invention is to provide a control rod assembly replacement operation system and method that can significantly improve the lifespan of control rod assemblies by replacing and circulating a bank (or single control rod assembly) that is not frequently used.

[0010] A method for operating the replacement of control rod assemblies according to one embodiment of the present invention comprises: a step of calculating the minimum burnup of control rod assemblies required per cycle for each bank of a reactor based on a nuclear power plant operation DB; a step of determining and classifying a control rod assembly as a disposal target if it has a burnup less than the product of the minimum burnup and the margin of a set value; a step of determining and classifying a control rod assembly having a burnup greater than or equal to the difference of the minimum burnup relative to 100% as a replaceable spare control rod assembly; a step of determining and classifying a control rod assembly having a burnup less than the difference of the minimum burnup relative to 100% and greater than or equal to a predetermined multiple of the product of the minimum burnup and the margin of a set value as a replacement target control rod assembly; a step of replacing the spare control rod assembly and the replacement target control rod assembly; and a step of managing the remaining control rod assemblies among the replacement target control rod assemblies as N+1 cycle targets.

[0011] According to a control rod assembly replacement operation system and method according to one embodiment of the present invention, even if the frequency of control rod usage increases due to load-following operation and the burnout of a specific bank becomes greater, causing a large difference in burnout between groups of control rod assemblies, and even if the difference in structural integrity inevitably occurs on a bank-by-bank basis, the lifespan of the control rod assemblies can be significantly improved by replacing and circulating with a bank (or single control rod assembly) that is not frequently used.

[0012] FIG. 1 is a plan view showing a nuclear fuel assembly and a control rod assembly,

[0013] FIG. 2 is a conceptual diagram explaining the insertion depth limit criteria for each bank of current operating nuclear power plants,

[0014] FIG. 3 is a block diagram showing the configuration of a control rod assembly replacement operation system according to an embodiment of the present invention,

[0015] FIG. 4 is a flowchart illustrating a method for operating a control rod assembly replacement according to an embodiment of the present invention,

[0016] FIG. 5 is an example diagram of control rod assembly burnup evaluation and replacement according to FIG. 4.

[0017] FIG. 6 is a diagram illustrating the control rod assembly exchange algorithm in FIG. 4, and

[0018] FIG. 7 is a diagram illustrating a method for integrally managing the burnup (life) of a control rod assembly.

[0019] The present invention will be described in more detail below with reference to the drawings. The drawings presented below are provided as examples to ensure that the concept of the present invention is sufficiently conveyed to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms. Furthermore, throughout the specification, the same reference numerals indicate the same components. It should be noted that the same components in the drawings are indicated by the same reference numerals wherever possible. Additionally, unless otherwise defined, technical and scientific terms used have the meaning commonly understood by those skilled in the art to which this invention pertains, and descriptions of known functions and configurations that could unnecessarily obscure the essence of the present invention are omitted in the following description and the accompanying drawings.

[0020] As the frequency of control rod usage increases due to load-following operation, the burnup of a specific bank becomes higher, which can lead to significant differences in burnup between groups of assemblies. Furthermore, differences in structural integrity can inevitably occur between banks. Therefore, replacing a bank (or single control rod assembly) that is not frequently used can significantly extend the lifespan of the control rod assemblies.

[0021] Now, with reference to FIG. 3, the control rod assembly replacement operation system of the present invention will be described.

[0022] FIG. 3 is a block diagram showing the configuration of a control rod assembly replacement operation system according to one embodiment of the present invention.

[0023] As illustrated in FIG. 3, a control rod assembly replacement operation system according to one embodiment of the present invention includes a control rod burnout judgment device (100) that determines the control rod burnout (A) using an operation DB (101), a structural integrity judgment device (200) that determines various structural integrity evaluation elements (B) in conjunction with a structural integrity DB (201) that evaluates various structural integritys such as unusable, caution, and good, and a replacement module device (300) that determines a replaceable control rod assembly by establishing a single control rod assembly replacement standard in conjunction with an integrated management DB (301) that manages a single control rod assembly.

[0024] The above control rod burnup determination device (100) comprises a minimum burnup calculation unit (110) that calculates the minimum burnup (a%, etc.) of a control rod assembly required per cycle per bank based on nuclear power plant operation experience, a disposal target determination unit (120) that classifies a control rod assembly as a replacement (disposal) target (C) when it has a burnup (life) less than [1.1 × a] by setting a margin of 10% for the minimum burnup, a margin target determination unit (130) that determines a control rod assembly having a burnup (life) of [100% - a%] or more as a replaceable control rod assembly (D), and a control rod assembly having a burnup (life) between [1.1 × a] and [(1.1 × a) × 2] as a replacement target (E) and extends its life by replacing (circulating) it with a control rod assembly (D) that has a burnup margin, and other control rod assemblies are replaced target (F) in the N+1 cycle It includes an N+1 cycle replacement target determination unit (140) managed in the operation DB (101).

[0025] The above structural integrity judgment device (200) may include a wear amount judgment unit (210) for judging the wear amount of various structures, a cladding thickness judgment unit (220) for judging the thickness of the cladding tube, a crack length judgment unit (230) for judging the crack length of the cladding tube, and other judgment units (240) related to structural integrity, and may be set with various structural integrity standards.

[0026] The above structural integrity judgment device (200) can determine whether the control rod assembly is subject to replacement (F) by comparing it with the design criteria values ​​(b[%], c[%], d[″]) of the above control rod burnup judgment device (100), and additionally, depending on the condition, the structural integrity DB (201) can be classified into unusable DB (201a), caution DB (201b), and good DB (201c) to manage the history.

[0027] The above replacement module device (300) may include a bank-unit replacement module (310) because, since the control rods are controlled in bank units, the burnup (life, use) of the control rod assembly within the same bank is almost identical, and as long as there is no particular problem with the integrity of the control rod assembly of a single control rod assembly within the same bank, it is convenient in terms of nuclear power plant operation to perform bank-unit replacement (circulation).

[0028] Additionally, the above replacement module device (300) may include a periodic replacement module unit (320) that determines the replacement module for each period by calculating the minimum burnup (a%) of the control rod assembly based on nuclear power plant operation experience and conservatively calculating the burnup of the control rod assembly to maximize the flexible operation period that can be performed each period.

[0029] The above replacement module device (300) may include a physical replacement module part (330) that performs the exchange of a control rod assembly by changing the physical position of the control rod assembly, and an algorithmic replacement module part (340) that performs the exchange of a control rod assembly by changing the control algorithm of the control rod assembly when the control rod assembly is exchanged within the same power plant (unit n).

[0030] Now, with reference to FIGS. 4 to 7, the method for operating the replacement of a control rod assembly according to the present invention will be described.

[0031] As illustrated in FIG. 4, according to an embodiment of the present invention, a control rod assembly replacement operation method determines a replaceable control rod assembly by establishing a single control rod assembly replacement criterion. The replacement criterion includes control rod burnout (A) and various structural integrity evaluation factors (B).

[0032] There are no restrictions on reactor types, such as PWRs and SMRs.

[0033] According to a control rod assembly replacement operation method according to one embodiment of the present invention, the minimum burnup calculation unit (110) calculates the minimum burnup (a%, etc.) of the control rod assembly required per cycle per bank based on nuclear power plant operation experience and starts a burnup evaluation (S110).

[0034] The disposal target determination unit (120) determines whether the burnup (a) is greater than the burnup margin value [1.1 × a] with a margin of 10% (S120), and if the burnup (life) is less than the burnup margin value [1.1 × a], the control rod assembly is classified as a replacement (disposal) target (C) (S121).

[0035] The above-mentioned margin target determination unit (130) determines whether the burnup margin value [1.1 × a], which is set to 10% margin for burnup (a), is greater than [100% - a%] because there is more remaining life than the minimum burnup (S130), and classifies the control rod assembly having a burnup (life) of [100% - a%] or greater as a replaceable margin control rod assembly (D) (S131).

[0036] The above N+1 cycle target determination unit (140) determines whether it has a burnup (life) smaller than [(1.1 × a) × 2] (S140), and classifies a control rod assembly having a burnup (life) between [1.1 × a] and [(1.1 × a) × 2] as an N+1 cycle replacement target (E) (S141).

[0037] If the burnup (life) is smaller than [(1.1 × a) × 2], it is determined to be a candidate for control rod assembly replacement (S150)

[0038] To determine whether a control rod assembly is eligible for replacement, the evaluation of replacement eligibility is initiated by assessing whether structural integrity is satisfied, independently of burnup.

[0039] The step of determining whether the structural integrity of the above control rod assembly is satisfied involves establishing an integrity judgment criterion (S210), determining whether the amount of wear is less than b[%] (S220), and classifying it as unusable or caution according to the history management criteria if the amount of wear is b[%] or greater (S221).

[0040] Determine whether the thickness of the cladding tube is less than c[%] (S230), and if the thickness of the cladding tube is greater than or equal to c[%], classify it as unusable or caution according to the history management criteria (S231).

[0041] It is determined whether the crack length is smaller than d["] (S240), and if the crack length is d["] or greater, it is classified as unusable or caution according to the history management criteria (S241).

[0042] For example, it is possible to determine whether the control rod assembly is subject to replacement (F) by comparing it with the design criteria (b[%], c[%], d[″]), and additionally, the history can be managed by classifying it into unusable, caution, and good stages depending on its condition.

[0043] Now, with reference to FIGS. 5 to 7, a method for operating a control rod assembly replacement according to an embodiment of the present invention according to FIG. 4 will be described in detail.

[0044] Figure 5 is an example of the burnup evaluation and replacement of a control rod assembly according to Figure 4.

[0045] Since control rods are controlled on a bank basis, the burnup (life, use) of control rod assemblies within the same bank is almost identical.

[0046] Therefore, if there is no particular problem with the integrity of a single control rod assembly within the same bank, it may be convenient from the perspective of nuclear power plant operation to perform bank-level replacement (rotation).

[0047] Based on nuclear power plant operation experience, the minimum burnup (a%) of control rod assemblies can be calculated. While this process can be somewhat complex when incorporating flexible operation, the burnup is conservatively calculated by maximizing the duration of flexible operation that can be performed per cycle.

[0048] As shown in Fig. 5, the burnup (life) of each bank is evaluated, and the necessity and feasibility of replacement are determined by comparing the minimum burnup (a%) required for one cycle, for example, N cycles, and, for example, Bank 5 and Bank 3 are replaced (circulated).

[0049] At this time, as illustrated in FIG. 4, the minimum burnup (a%, etc.) required per cycle for each bank can be calculated based on nuclear power plant operation experience, and a margin of 10% is set so that if the burnup (life) is less than [1.1 × a], the control rod assembly is considered for replacement (disposal) (C), if the burnup (life) is greater than [100% - a%], the control rod assembly is considered a replaceable control rod assembly (D), and if the burnup (life) is between [1.1 × a] and [(1.1 × a) × 2], the control rod assembly is considered for replacement (E).

[0050] The control rod assembly can be replaced by changing the physical location of the above control rod assembly. For example, a method can be applied in which the control rod assembly to be replaced is temporarily stored in an SFP and then assembled in its original location.

[0051] Figure 6 is a diagram illustrating the control rod assembly exchange algorithm in Figure 4.

[0052] When exchanging control rod assemblies within the same power plant (Unit n), the exchange of control rod assemblies can be performed by changing the control algorithm of the control rod assemblies.

[0053] As illustrated in FIG. 6, the step of giving a first signal (cable, etc.) to Bank #5, which is the target of exchange in the existing control rod assembly control logic (S341) and the step of giving a second signal (cable, etc.) to Bank #3 (S342) can be replaced with the step of giving a second signal (cable, etc.) to Bank #5, which is the target of exchange in the new control rod assembly control logic (S342) and the step of giving a first signal (cable, etc.) to Bank #3 (S341).

[0054] In cases where multiple modules coexist within a single power plant, such as in Small Modular Reactors (SMRs), control rod assemblies can be replaced in various ways.

[0055] As SMRs are expected to operate under load-following conditions at a high frequency, the burnup of control rod assemblies may vary by module. Therefore, burnup is managed integrally to select replaceable control rod assemblies and perform replacement (rotation).

[0056] In nuclear power plants with multiple modules, such as SMRs, the burnup (life) of control rod assemblies can be determined for each module to perform the replacement (rotation) of control rod assemblies between banks. At this time, the banks subject to replacement are not limited to the same module.

[0057] Figure 7 is a diagram illustrating a method for integrally managing the burnup (life) of a control rod assembly.

[0058] As shown in Fig. 7, the initial core has a lifespan of 100% for each bank, and after one cycle of combustion, usage varies by bank in Modules A to D and the lifespan can be calculated differently.

[0059] After two cycles of combustion, modules A and B are modules that perform maximum elastic operation, and by assuming that banks #5 to #1 all have the same performance (materials, configuration, etc.), the burnup (life) of the control rod assemblies can be managed integrally so that bank 5 of module A and bank 5 of module B can be replaced.

[0060] After the third cycle of combustion, modules A and B are modules that perform maximum elastic operation, and by assuming that banks #5 to #1 all have the same performance (materials, configuration, etc.), the burnup (life) of the control rod assemblies is managed integrally, so that bank 5 of module A and bank 5 of module B are targeted for disposal, and banks 4 and 3 can be replaced.

[0061] Even when the banks to be replaced are different modules, the control rod assembly replacement target can be determined by the control rod assembly replacement operation method according to an embodiment of the present invention of FIG. 4. Similarly, different burnout levels (a, b, c...%) can be set for each bank to operate in a complex manner.

[0062] If changes are made within the same module, the algorithm can be modified and applied without any physical changes.

[0063]

[0064]

[0065] According to a control rod assembly replacement operation system and method according to one embodiment of the present invention, even if the frequency of control rod usage increases due to load-following operation and the burnout of a specific bank becomes greater, causing a large difference in burnout between groups of control rod assemblies, and even if the difference in structural integrity inevitably occurs on a bank-by-bank basis, the lifespan of the control rod assemblies can be significantly improved by replacing and circulating with a bank (or single control rod assembly) that is not frequently used.

Claims

1. A step of calculating the minimum burnup of control rod assemblies required per cycle per reactor bank based on the nuclear power plant operation DB; A step of determining and classifying a control rod assembly as a disposal target if it has a burnup less than the product of the minimum burnup and the margin of the set value; A step of determining and classifying a control rod assembly having a burnup greater than or equal to the difference in minimum burnup relative to 100% as a replaceable spare control rod assembly; A step of determining and classifying a control rod assembly as a replacement target control rod assembly having a burnup degree smaller than the difference from the minimum burnup degree to the above 100% and greater than a predetermined multiple of the product of the minimum burnup degree and the margin of the set value; A step of replacing the above spare control rod assembly and the above replacement target control rod assembly; and A control rod assembly replacement operation method comprising the step of managing the remaining control rod assemblies among the above-mentioned replacement target control rod assemblies as N+1 cycle replacement targets.

2. In Paragraph 1, The method further includes a step of determining whether the structural integrity of the control rod assembly is satisfied, The step of determining whether the structural integrity of the control rod assembly is satisfied includes the step of determining whether the control rod assembly is a control rod assembly subject to replacement by comparing the amount of wear of various structures, the thickness of the cladding, and the crack length with design criteria. A method for operating a control rod assembly replacement, comprising a step of determining whether the structural integrity of the control rod assembly is satisfied, and a step of managing the history by classifying it into unusable, caution, and good stages according to the condition compared with the design criteria.

3. In Paragraph 2, The step of replacing the above spare control rod assembly and the above replacement target control rod assembly is a control rod assembly replacement operation method in which a single control rod assembly within the same bank satisfies the above structural integrity and is replaced on a bank basis.

4. In Paragraph 1, The step of calculating the minimum burnup of the control rod assembly required per cycle for each bank includes the step of calculating the burnup of the control rod assembly by maximizing the flexible operation period that can be performed per cycle, and A control rod assembly replacement operation method comprising the step of evaluating the burnup of each bank by period and determining whether replacement is necessary and possible through comparison with the minimum burnup required for one period.

5. In Paragraph 1, The step of replacing the above spare control rod assembly and the above replacement target control rod assembly is a control rod assembly replacement operation method that replaces the above spare control rod assembly and the above replacement target control rod assembly by changing the physical position.

6. In Paragraph 1, The step of replacing the above spare control rod assembly and the above replacement target control rod assembly is a control rod assembly replacement operation method in which the exchange is performed by changing the control algorithm when replacing the above spare control rod assembly and the above replacement target control rod assembly within the same power plant.

7. In Paragraph 6, A control rod assembly replacement operation method comprising the step of performing an exchange by changing the control algorithm above, which includes the step of exchanging signals between the spare control rod assembly and the control rod assembly to be replaced.

8. In Paragraph 1, The above reactor is an SMR that performs load-following operation, and A step for integrally managing different burnup degrees of control rod assemblies for each SMR module, and A control rod assembly replacement operation method that determines the burnout of the control rod assemblies for each module and performs control rod assembly replacement between banks.

9. In Paragraph 8, A control rod assembly replacement operation method that integrally manages the burnup of control rod assemblies by assuming that the banks to be replaced are different first and second modules, that the first and second modules perform elastic operation to the maximum, and that all banks have the same performance (material, configuration, etc.).

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