A decision-making method for steam generator replacement in operating nuclear power units

Abstract

The present invention discloses a steam generator replacement decision-making method for an operating nuclear power unit, comprising the following steps: screening some components of the steam generator to participate in the decision-making evaluation and using them as target components; classifying the target components and assigning different numerical values to each of them as active evaluation indicators corresponding to each target component; calculating the failure probability distribution of the target components of the steam generator, and taking the vertical coordinate from the failure probability distribution as a passive evaluation indicator according to the probability requirement; calculating the comprehensive evaluation score of the steam generator based on the active evaluation indicators and passive evaluation scores of each target component, and assigning different numerical ranges of the comprehensive evaluation score to each decision; and taking corresponding decisions based on the numerical range into which the comprehensive evaluation score falls. The steam generator replacement decision-making method for an operating nuclear power unit provided by the present invention can accurately and quickly determine the replacement or maintenance operation, thereby improving overall safety.

Description

Technical Field

[0001] The present invention relates to the technical field of steam generator operation and maintenance, and in particular to a steam generator replacement decision method for an operating nuclear power unit. Background Art

[0002] Steam generators are key components of the primary circuit of a nuclear power plant. Their primary function is to transfer heat from the primary coolant to the secondary feedwater, generating saturated steam for the secondary power plant. They are a crucial component of the primary circuit's pressure boundary and a crucial safety barrier against radioactive leaks. Domestic steam generators are typically designed for a lifespan of 40 to 60 years, and as their lifespan nears, they inevitably face replacement.

[0003] According to the national nuclear power development plan, construction of 6-8 nuclear power units will begin annually over the coming period, leading to an increasing number of commercial nuclear power units in China. Consequently, the industry is urgently demanding steam generator replacement technology for operating nuclear power plants. Scientific and technological research and development are needed to address these shortcomings and master steam generator replacement technology for operating nuclear power plants.

[0004] The decision-making criteria for steam generator replacement in operating nuclear power units is one of the key cores of steam generator replacement technology in operating nuclear power plants. It is an important judgment to determine the timing of steam generator replacement and has key guiding significance for steam generator replacement.

[0005] At present, decision-making criteria for replacing steam generators in operating nuclear power units have not been established at home and abroad. There are no relevant scoring methods and evaluation indicators, and it is impossible to simultaneously assess whether the various components of the steam generator can continue to serve and whether these components can be repaired or replaced individually.

[0006] The disclosure of the above background technology content is only used to assist in understanding the inventive concept and technical solution of the present invention. It does not necessarily belong to the prior art of this patent application, nor does it necessarily provide technical guidance. In the absence of clear evidence that the above content has been disclosed before the filing date of this patent application, the above background technology should not be used to evaluate the novelty and creativity of this application. Summary of the Invention

[0007] In order to overcome the shortcomings of the existing technology, the present invention provides a steam generator replacement decision method for an operating nuclear power unit. The specific technical solution is as follows: A steam generator replacement decision method for an operating nuclear power unit comprises the following steps:

[0008] Based on the factors influencing the replacement of steam generators, select some components of steam generators to participate in decision-making evaluation and use them as target components;

[0009] Classifying the target components according to their corresponding design information and engineering technology into categories including components that cannot be repaired and replaced, components that cannot be repaired but can be replaced, and components that can be repaired but cannot be replaced, and assigning different values to each of the categories as active evaluation indicators corresponding to the target components;

[0010] The failure probability distribution of the target components of the steam generator is calculated. According to the probability requirement, the vertical coordinate is taken from the failure probability distribution as the passive evaluation index. After the passive evaluation index PEI is normalized, the passive evaluation score of each target component is obtained.

[0011] Based on the active evaluation index AEI and passive evaluation score PES of each target component, the comprehensive evaluation score CES of the steam generator is calculated. The calculation formula is as follows:

[0012] CES=min[AEI1*(PES1+1),AEI2*(PES2+1),…,AEI i *(PES i +1),…,AEI n *(PES n +1)]

[0013] Where i is the target component number, n is the total number of target components;

[0014] The steam generator replacement decision includes replacing the steam generator as a whole, replacing components of the steam generator, repairing components of the steam generator, and no need to repair or replace the steam generator; each decision is assigned a different numerical range of the comprehensive evaluation score; and a corresponding decision is taken based on the numerical range into which the comprehensive evaluation score falls.

[0015] Furthermore, the design information and engineering technology corresponding to the target component are quantitatively assigned values, denoted as K1 and K2 respectively. If the design information explicitly prohibits both component replacement and component repair, then K1 takes the value of 0. If the design information explicitly prohibits only component replacement, then K1 takes the value of x1. If the design information explicitly prohibits only component repair, then K1 takes the value of y1.

[0016] If the engineering technology cannot achieve component replacement and repair, then K2 takes the value of 0; if the engineering technology cannot achieve component replacement but can achieve component repair, then K2 takes the value of x2; if the engineering technology can achieve component replacement but cannot achieve component repair, then K2 takes the value of y2;

[0017] When classifying the target components, it is necessary to calculate the maintenance parameter MTP of the steam generator components. The calculation formula is as follows:

[0018] MTP=K1×K2

[0019] If MTP∈(0, x1y2, x2y1), the corresponding target component cannot be repaired and cannot be replaced. If MTP=y1y2, the corresponding target component cannot be repaired but can be replaced. If MTP=x1x2, the corresponding target component can be repaired but cannot be replaced.

[0020] Furthermore, if the target component cannot be repaired and cannot be replaced, the active evaluation index value is a; if the target component cannot be repaired but can be replaced, the active evaluation index value is b; if the target component can be repaired but cannot be replaced, the active evaluation index value is c; a, b, and c are all positive numbers, 2a<b, 2b<c.

[0021] Furthermore, a, b, and c are values of different orders of magnitude.

[0022] Furthermore, when the passive evaluation score PES ≤ σ, the target component does not meet the service conditions and cannot continue to serve; when the passive evaluation score PES > σ, the target component meets the service conditions and can continue to serve, but a decision needs to be made based on the comprehensive evaluation score to perform corresponding operations; where σ is the component service safety limit, 0 ≤ σ ≤ 1.

[0023] Furthermore, the calculation formula for the normalized passive evaluation index PEI is as follows:

[0024]

[0025] Where i is the target component number, PEI max It is the maximum passive evaluation score among all target components.

[0026] Furthermore, if the comprehensive evaluation score CES is not within any decision-making numerical range, the steam generator does not need to be repaired or replaced.

[0027] Furthermore, design information and in-service inspection information of target components of the steam generator are collected and recorded.

[0028] Furthermore, the target components include a heat transfer tube bundle, a water supply ring, and a lower head.

[0029] Furthermore, the Monte Carlo method is used to calculate the failure probability distribution of the target components of the steam generator.

[0030] Compared with the existing technology, the present invention has the following advantages: by setting the active evaluation index AEI and the passive evaluation index PEI to assign values to the conditions of each component, and through the calculation model of the comprehensive evaluation score, the comprehensive evaluation score CES of each component falls into different intervals according to its actual situation. The calculation model can also avoid the overlap of intervals in different situations, thereby achieving fast and accurate decision-making. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a flow chart of a steam generator replacement decision-making method for an operating nuclear power unit provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0033] It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and the accompanying drawings are used to distinguish similar items and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, such that the embodiments of the present invention described herein can be implemented in sequences other than those illustrated or described herein. Furthermore, the terms "including," "having," and any variations thereof are intended to cover non-exclusive inclusions.

[0034] In one embodiment of the present invention, a method for making a decision on steam generator replacement for an operating nuclear power unit is provided, comprising the following steps:

[0035] According to the factors affecting the replacement of the steam generator, some components of the steam generator are screened to participate in the decision-making evaluation and are used as target components; the design information and in-service inspection information of the target components of the steam generator are collected and recorded.

[0036] Classifying the target components according to their corresponding design information and engineering technology into categories including components that cannot be repaired and replaced, components that cannot be repaired but can be replaced, and components that can be repaired but cannot be replaced, and assigning different values to each of the categories as active evaluation indicators corresponding to the target components;

[0037] The design information and engineering technology corresponding to the target component are quantitatively assigned values, denoted as K1 and K2 respectively. If the design information explicitly prohibits both component replacement and component repair, then K1 takes the value of 0. If the design information explicitly prohibits only component replacement, then K1 takes the value of x1. If the design information explicitly prohibits only component repair, then K1 takes the value of y1.

[0038] If the engineering technology cannot achieve component replacement and repair, then K2 takes the value of 0. If the engineering technology cannot achieve component replacement but can achieve component repair, then K2 takes the value of x2. If the engineering technology can achieve component replacement but cannot achieve component repair, then K2 takes the value of y2, where x1≠y1 and x2≠y2.

[0039] When classifying the target components, it is necessary to calculate the maintenance parameter MTP of the steam generator component, which represents whether the steam generator component can be repaired or replaced. The calculation formula is as follows:

[0040] MTP=K1×K2

[0041] If MTP∈(0, x1y2, x2y1), the corresponding target component cannot be repaired or replaced. If MTP=y1y2, the corresponding target component cannot be repaired but can be replaced. If MTP=x1x2, the corresponding target component can be repaired but cannot be replaced. If the target component cannot be repaired or replaced, the active evaluation index value is a. If the target component cannot be repaired but can be replaced, the active evaluation index value is b. If the target component can be repaired but cannot be replaced, the active evaluation index value is c. a, b, and c are all positive numbers, 2a<b, 2b<c, and a, b, and c are values of different orders of magnitude.

[0042] The Monte Carlo method is used to calculate the failure probability distribution of the target components of the steam generator. The vertical coordinate of the failure probability distribution is taken as the passive evaluation index according to the probability requirement P. The value range of P is: 0<P<1. After normalizing the passive evaluation index PEI, the passive evaluation score of each target component is obtained.

[0043] The calculation formula for the normalized passive evaluation index PEI is as follows:

[0044]

[0045] Where i is the target component number, PEI max It is the maximum passive evaluation score among all target components.

[0046] The passive evaluation score PES represents the service status of each component of the steam generator. When the passive evaluation score PES ≤ σ, the target component does not meet the service conditions and cannot continue to serve. When the passive evaluation score PES > σ, the target component meets the service conditions and can continue to serve, but a decision needs to be made based on the comprehensive evaluation score to perform corresponding operations. Among them, σ is the component service safety limit, 0 ≤ σ ≤ 1.

[0047] Based on the active evaluation index AEI and passive evaluation score PES of each target component, the comprehensive evaluation score CES of the steam generator is calculated. The calculation formula is as follows:

[0048] CES=min[AEI1*(PES1+1),AEI2*(PES2+1),…,AEI i *(PES i +1),…,AEI n *(PES n +1)]

[0049] Where i is the target component number, and n is the total number of target components.

[0050] The steam generator replacement decision includes replacing the entire steam generator, replacing steam generator components, repairing steam generator components, and not repairing or replacing the steam generator. Each decision is pre-assigned a different comprehensive evaluation score numerical range. The corresponding decision is made based on the numerical range in which the comprehensive evaluation score falls. If the comprehensive evaluation score CES does not fall within the numerical range of any decision, then the steam generator does not need to be repaired or replaced. Specifically, if the value of the comprehensive evaluation score CES is within the range [a, 2a], then the entire steam generator needs to be replaced. If the value of the comprehensive evaluation score CES is within the range [b, 2b], then the steam generator components need to be replaced, and the entire steam generator does not need to be replaced. If the value of the comprehensive evaluation score CES is within the range [c, 2c], then the steam generator components need to be repaired, and there is no need to replace the entire steam generator or replace the steam generator components. If the value of the comprehensive evaluation score CES is not within any of the above ranges, then the steam generator does not need to be repaired or replaced. Among them, the numerical ranges of the comprehensive evaluation scores corresponding to the overall replacement of the steam generator, replacement of steam generator components, and repair of steam generator components are [a, 2a], [b, 2b], and [c, 2c], respectively. The numerical range of the comprehensive evaluation score corresponding to the situation where there is no need to repair or replace the steam generator is the numerical range excluding the above three ranges.

[0051] In one embodiment of the present invention, see Figure 1 , the steam generator replacement decision-making method includes the following steps:

[0052] Step 1. Based on the feedback from domestic and international peers and the service status of each steam generator component, select the steam generator components that need to be included in the steam generator replacement decision criteria for operating nuclear power units: heat transfer tube bundle, feedwater ring, and lower head;

[0053] Step 2. Collect and record the design information and in-service inspection information of the steam generator's heat transfer tube bundle, water feed ring, and lower head;

[0054] Step 3. Based on design information and engineering expertise, the heat transfer tube bundle cannot be repaired or replaced as a whole. The active evaluation index (AEI) value is a = 0.1. The feedwater ring can be replaced. The active evaluation index (AEI) value is b = 1. The lower head can be repaired. The active evaluation index (AEI) value is c = 10. At this point, the comprehensive evaluation score ranges for replacing the entire steam generator, replacing steam generator components, and repairing steam generator components are [0.1, 0.2], [1, 2], and [10, 20], respectively. The remaining range corresponds to no need for steam generator repair or replacement.

[0055] Step 4. Calculate the passive evaluation index (PEI) of each steam generator component based on the in-service inspection information and the preset evaluation model. The PEI of the heat transfer tube bundle is 70; the PEI of the feedwater ring is 80; and the PEI of the lower head is 98.

[0056] According to the normalization formula:

[0057]

[0058] The passive evaluation score PES of the heat transfer tube bundle is 0.714; the passive evaluation score PES of the water supply ring is 0.816; the passive evaluation score PES of the lower head is 1.00, and the value of σ is 0.8;

[0059] Step 5. Based on the active evaluation index AEI and passive evaluation score PES of the heat transfer tube bundle, water supply ring, and lower head, the comprehensive evaluation score CES of the steam generator is calculated to be 0.1714.

[0060] Step 6. The value of the comprehensive evaluation score CES of the steam generator is in the range of [0.1, 0.2], and the steam generator needs to be replaced as a whole.

[0061] The steam generator replacement decision-making method provided by the present invention assigns values to the conditions of each component by setting an active evaluation index AEI and a passive evaluation index PEI, and uses a calculation model for the comprehensive evaluation score to ensure that the comprehensive evaluation score CES of each component falls within different intervals according to its actual situation. The calculation model can also avoid overlap of intervals for different situations, thereby achieving fast and accurate decision-making.

[0062] The above description is only a preferred embodiment of the present invention and does not limit the scope of the patent. Any equivalent structure or equivalent process transformation made by using the contents of the description and drawings of the present invention, directly or indirectly applied in other related technical fields, is also included in the scope of patent protection of the present invention.

Claims

1. A steam generator replacement decision method for an operating nuclear power unit, characterized in that: The following steps are involved: Based on the factors influencing the replacement of steam generators, select some components of steam generators to participate in decision-making evaluation and use them as target components; Classifying the target components according to their corresponding design information and engineering technology into categories including components that cannot be repaired and replaced, components that cannot be repaired but can be replaced, and components that can be repaired but cannot be replaced, and assigning different values to each of the categories as active evaluation indicators corresponding to the target components; The failure probability distribution of the target components of the steam generator is calculated. According to the probability requirement, the vertical coordinate is taken from the failure probability distribution as the passive evaluation index. After the passive evaluation index PEI is normalized, the passive evaluation score of each target component is obtained. Based on the active evaluation index AEI and passive evaluation score PES of each target component, the comprehensive evaluation score CES of the steam generator is calculated. The calculation formula is as follows: CES=min[AEI1*(PES1+1),AEI2*(PES2+1),…,AEI i *(PES i +1),…,AEI n *(PES n +1)] Where i is the target component number, n is the total number of target components; The steam generator replacement decision includes replacing the entire steam generator, replacing steam generator components, repairing steam generator components, and not repairing or replacing the steam generator; each decision is assigned a different numerical range of a comprehensive evaluation score; and a corresponding decision is taken based on the numerical range in which the comprehensive evaluation score falls. Quantify the design information and engineering technology corresponding to the target component and assign them values, denoted as K1 and K2 respectively. If the design information explicitly prohibits both component replacement and component repair, then K1 is 0. If the design information explicitly prohibits only component replacement, then K1 is x1. If the design information explicitly prohibits only component repair, then K1 is y1. If the engineering technology cannot achieve component replacement and repair, then K2 takes the value of 0; if the engineering technology cannot achieve component replacement but can achieve component repair, then K2 takes the value of x2; if the engineering technology can achieve component replacement but cannot achieve component repair, then K2 takes the value of y2; When classifying the target components, it is necessary to calculate the maintenance parameter MTP of the steam generator components. The calculation formula is as follows: MTP=K1×K2 If MTP∈(0, x1y2, x2y1), the corresponding target component cannot be repaired and cannot be replaced. If MTP=y1y2, the corresponding target component cannot be repaired but can be replaced. If MTP=x1x2, the corresponding target component can be repaired but cannot be replaced. If the target component cannot be repaired and cannot be replaced, the active evaluation index value is a; if the target component cannot be repaired but can be replaced, the active evaluation index value is b; if the target component can be repaired but cannot be replaced, the active evaluation index value is c; a, b, and c are all positive numbers, 2a<b, 2b<c.

2. The steam generator replacement decision method according to claim 1, characterized in that: a, b, and c are numerical values of different orders of magnitude.

3. The steam generator replacement decision method according to claim 1, characterized in that: When the passive evaluation score PES ≤ σ, the target component does not meet the service conditions and cannot continue to serve; when the passive evaluation score PES > σ, the target component meets the service conditions and can continue to serve, but a decision needs to be made based on the comprehensive evaluation score to perform corresponding operations; where σ is the component service safety limit, 0 ≤ σ ≤ 1.

4. The steam generator replacement decision method according to claim 1, characterized in that: The calculation formula for the normalized passive evaluation index PEI is as follows: Where i is the target component number, PEI max It is the maximum passive evaluation score among all target components.

5. The steam generator replacement decision method according to claim 1, characterized in that: If the comprehensive evaluation score CES is not within any decision-making value range, the steam generator does not need to be repaired or replaced.

6. The steam generator replacement decision method according to claim 1, characterized in that: The numerical ranges of the comprehensive evaluation scores for replacing the entire steam generator, replacing the components of the steam generator, and repairing the components of the steam generator are [a, 2a], [b, 2b], and [c, 2c] respectively.

7. The steam generator replacement decision method according to claim 1, characterized in that: The target components include a heat transfer tube bundle, a water supply ring, and a lower head.

8. The steam generator replacement decision method according to claim 1, characterized in that: The Monte Carlo method is used to calculate the failure probability distribution of target components of steam generators.

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