Method for analyzing influence of overhaul cycle on initiating event of multi-module high temperature gas cooled reactor

Abstract

The present application belongs to the field of nuclear safety analysis, in particular to the field of probabilistic safety analysis of multi-module nuclear power plant, and more particularly to a method for analyzing the influence of the overhaul cycle of multi-module high-temperature gas-cooled reactor on initiating event, comprising: step 1, dividing operating conditions to determine the overhaul cycle and the duration of the overhaul under different operating conditions; step 2, identifying the list of initiating events under different operating conditions by using the FMEA method; step 3, calculating the annual average share of each operating condition; step 4, calculating the total annual average frequency of initiating events; and step 5, calculating the annual average frequency of initiating events under each operating condition. The method can make the results of initiating event analysis more consistent with the actual operation of the nuclear power plant, thereby reducing the uncertainty of the PSA model and making the quantitative results of the PSA more accurate.

Description

Technical Field

[0001] This invention belongs to the field of nuclear safety analysis, and particularly relates to the field of probabilistic safety analysis of multi-module reactor nuclear power plants. Specifically, it relates to a method for analyzing the impact of overhaul cycles on initiating events in multi-module high-temperature gas-cooled reactors. Background Technology

[0002] High-temperature gas-cooled reactor (HTGR) nuclear power plants deploy multiple modular reactors, with each module consisting of two reactors. Multiple modules together form a single unit for heating and power generation. To ensure the continuous and stable production of high-quality industrial steam, the unit design employs a periodic, rotating overhaul scheme for each module. When one module enters a shutdown maintenance period, the other modules continue operating normally and producing industrial steam. Extending the overhaul cycle reduces the economic losses caused by frequent shutdowns, thereby effectively improving the economic efficiency of the HTGR nuclear power plant. One prerequisite for implementing long-cycle overhauls is analyzing the impact of long-cycle overhauls on probabilistic safety analysis (PSA) to assess whether the impact of long-cycle overhauls on the safety of the nuclear power plant is within acceptable limits.

[0003] Initiating event analysis (IPA) is the starting point for Power Condition Internal Event Analysis (PSA) of a nuclear power plant. Its purpose is to identify events that cause disturbances to the nuclear power plant and may lead to radioactive releases, and to calculate the annual average frequency of such events as input for the PSA model. Because high-temperature gas-cooled reactors (HTGRs) have a multi-module design, the scope of influence of a specific initiating event must be identified in IPA, i.e., whether the initiating event affects a single module reactor or multiple modules.

[0004] Existing methods exist for identifying multi-module initiation events, but these methods only consider the identification of multi-module initiation events when all modules of the unit are in power operation. They do not consider the changes in the initiation event list when each module of the multi-module high-temperature gas-cooled reactor unit is in power operation and overhaul respectively, nor can they analyze the impact of extended overhaul cycles on the frequency of initiation events.

[0005] To accurately analyze the impact of long-cycle overhauls on the safety of multi-module high-temperature gas-cooled reactor nuclear power plants, and thus support the adoption of longer overhaul cycles to improve the operational economy of nuclear power plants, a new method is needed to identify the impact of long-cycle overhauls on the initiation events and their frequency in nuclear power plants. Summary of the Invention

[0006] The purpose of this invention is to provide a method for analyzing the impact of overhaul cycles on initiation events in multi-module high-temperature gas-cooled reactors. This method identifies newly added multi-module initiation events in nuclear power plants under single-module overhaul conditions by analyzing overhaul plans and multi-module initiation event lists. It also calculates the frequency of these events, making the results of initiation event analysis more consistent with the actual operation of nuclear power plants. This reduces the uncertainty of the PSA model and makes the quantitative results of PSA more accurate.

[0007] Technical solution to achieve the purpose of this invention: A method for analyzing the impact of overhaul cycles on initiating events in multi-module high-temperature gas-cooled reactors, the method comprising: Step 1: Divide the operating conditions and determine the overhaul cycle and duration of overhaul for different operating conditions; Step 2: Use the FMEA method to identify the list of initiating events under different operating conditions; Step 3: Calculate the average annual share for each operating condition; Step 4: Calculate the total annual average frequency of the initiating event; Step 5: Calculate the annual average frequency of the initiating event under each operating condition.

[0008] Furthermore, the operating conditions include full unit power operation, single module overhaul, and full unit overhaul.

[0009] Further, step 2 includes: Step 2.1: List all systems within the analysis boundary of the high-temperature gas-cooled reactor nuclear power plant; Step 2.2: Based on the system functions and composition, analyze each failure mode and its failure impact under three operating conditions: full unit power operation, single module overhaul, and full unit overhaul. Step 2.3: Determine the failure impact of the failure mode and identify the initiating events under the three operating conditions; Step 2.4: Classify the initiating events to form a list of initiating events of different categories under the three operating conditions.

[0010] Furthermore, the method for determining the initiating event in step 2.3 is as follows: determine whether the failure effect of a specific failure mode of the system will cause one or more module stacks to trigger an emergency shutdown. If so, the emergency shutdown caused by the failure of the system is an initiating event.

[0011] Furthermore, in step 2.3, for the different system configurations under the three operating conditions of full unit power operation, single module overhaul, and full unit overhaul, the emergency shutdown caused by system failure under the three operating conditions is determined, and the initiation event under each of the three operating conditions is obtained.

[0012] Furthermore, in step 2.3, determining whether the failure impact of a specific failure mode of the system will cause one or more module stacks to trigger an emergency shutdown further includes: for different system configurations under three operating conditions—full unit power operation, single module overhaul, and full unit overhaul—determining which failure modes of the system will trigger an emergency shutdown of one or more module stacks under each of the three operating conditions, identifying which module stacks(s) will trigger the emergency shutdown, and determining the module stacks(s) affected by the system failure.

[0013] Further, step 2.4 specifically involves classifying the determined initiating events according to their type and the number of affected modules to obtain a series of single-module initiating events, dual-module initiating events, and multi-module initiating events, forming complete initiating event lists for the three operating conditions.

[0014] Furthermore, the formula for calculating the annual average share of each operating condition in step 3 is as follows: ; ; ; Among them, F1, F2, and F3 represent the annual average share of three operating conditions: full unit power operation, single module overhaul, and full unit overhaul, respectively; n represents the number of modules in the high-temperature gas-cooled reactor nuclear power plant; T cycle,m For single module overhaul cycle, T cycle,u For the overhaul cycle of the entire unit, T outage,m For single-module overhaul duration, T outage,u The duration of the overhaul of the entire unit.

[0015] Furthermore, in step 5, the method for calculating the annual average frequency of the initiating event under each operating condition is to multiply the total annual average frequency of the initiating event by the annual average share of the operating condition to obtain the annual average frequency of the initiating event under that operating condition.

[0016] Furthermore, the method also includes: Step 6: Evaluate the impact of long-cycle overhauls on the frequency of initiating events: Substitute different overhaul cycles into Step 3 to obtain the annual average share of each operating condition corresponding to different overhaul cycles; further substitute into Step 5 to obtain the annual average frequency of initiating events under each operating condition corresponding to different overhaul cycles.

[0017] The beneficial technical effects of this invention are as follows: 1. The method of the present invention divides the operating conditions of nuclear power plants, identifies the initiating events under different operating conditions, and calculates the annual average frequency of different initiating events under each operating condition based on the annual average share of each operating condition. This makes the results of initiating event analysis more consistent with the actual operating conditions of nuclear power plants, thereby reducing the uncertainty of the PSA model and making the quantitative results of PSA more accurate. 2. The method of this invention can analyze the impact of changes in the overhaul cycle on the frequency of initiating events. As a component of the analysis of the impact of long-cycle overhauls on PSA, it can effectively support the feasibility demonstration of long-cycle overhaul schemes and help long-cycle overhaul schemes gain the approval of nuclear safety regulatory authorities.

[0018] 3. The method of the present invention effectively solves the technical defects of the previous technology, which can only identify the initiation events of all modules of a multi-module high-temperature gas-cooled reactor nuclear power plant when they are in power operation conditions, without considering the changes of multi-module initiation events when the whole unit is in power operation conditions or when a single module enters the overhaul shutdown condition, and also cannot analyze the impact of the extension of the overhaul cycle on the frequency changes of multi-module initiation events. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the embodiments.

[0020] This invention provides a method for analyzing the impact of overhaul cycles on initiating events in multi-module high-temperature gas-cooled reactors, specifically including the following steps: Step 1: Divide the operating conditions and determine the overhaul cycle and duration of overhaul for different operating conditions.

[0021] Because high-temperature gas-cooled reactor (HTGR) nuclear power plants have different system configurations under different operating conditions, these differences can lead to variations in the initiation events and their frequencies under different operating conditions. Therefore, based on the characteristics of the HTGR nuclear power plant's operation and maintenance strategy, the unit's operating conditions should be divided into at least three different operating conditions, including but not limited to full unit power operation, single module overhaul, and full unit overhaul. Furthermore, the single module overhaul cycle T should be determined based on the overhaul cycle and overhaul duration specified in the nuclear power plant's operation and maintenance strategy. cycle,m The overhaul cycle of the entire unit is T cycle,u Single module overhaul duration T outage,m The duration of the entire unit overhaul is T. outage,u .

[0022] In a specific implementation, the two sets of typical values ​​are as follows: (1) The actual / planned execution cycle and duration of the high-temperature gas-cooled reactor nuclear power plant are as follows: T cycle,m =2 years, T cycle,u =6 years, T outage,m = T outage,u=February; (2) The target values ​​for the cycle and duration that a high-temperature gas-cooled reactor nuclear power plant is expected to achieve in the future through long-cycle overhaul analysis and demonstration methods are: T cycle,m =3 years, T cycle,u =9 years, T outage,m = T outage,u =February. This method is a component of the long-cycle overhaul analysis and demonstration method.

[0023] Step 2: Use the FMEA method to identify the list of initiating events under different operating conditions.

[0024] The specific steps include: Step 2.1: List all systems within the analysis boundary of the high-temperature gas-cooled reactor nuclear power plant; Step 2.2: Based on the system's functions and composition, analyze each failure mode and its impact under the three operating conditions. System failure modes and failure effects are related to the system's function and structural composition. Starting from the system function, the failure mode is the failure of a specific function of the system, while the failure effect requires determining what impact the failure of the system function will have on the nuclear power plant.

[0025] For different system configurations under three operating conditions—full unit power operation, single module overhaul, and full unit overhaul—the failure modes and failure effects of the system under each of the three conditions are determined.

[0026] Step 2.3: Determine the failure impact of the failure mode and identify the initiating events under the three operating conditions. Determine whether the failure effect of a specific failure mode of the system will cause one or more modules to trigger an emergency shutdown. If so, the emergency shutdown caused by the system failure is a triggering event. Triggering an emergency shutdown includes automatically triggered emergency shutdowns and manually triggered emergency shutdowns.

[0027] For different system configurations under three operating conditions—full unit power operation, single module overhaul, and full unit overhaul—the emergency shutdown caused by system failure under each of the three operating conditions is determined, and the initiation event under each of the three operating conditions is obtained.

[0028] Different failure modes of the same system may affect different module reactors; even for the same failure mode, the scope of its impact may change under different operating conditions due to changes in the operating configuration of the nuclear power plant.

[0029] Determining whether the failure effect of a specific failure mode in the system would lead to an emergency shutdown of one or more modules further includes: For different system configurations under three operating conditions—full unit power operation, single module overhaul, and full unit overhaul—it is determined which failure modes will trigger an emergency shutdown of one or more module stacks under each of the three operating conditions, and which module stacks or modules will trigger the emergency shutdown, thus identifying the module stacks affected by the system failure.

[0030] Based on the emergency shutdowns triggered by the module stacks affected by system failures under the three operating conditions, the initiation events for each of the three operating conditions are obtained.

[0031] Step 2.4: Classify the initiating events to form a list of initiating events of different categories under the three operating conditions. The initiating events identified in the above steps are categorized according to their type and the number of affected modules, resulting in a series of single-module initiating events, dual-module initiating events, and multi-module initiating events, forming complete initiating event lists for three different operating conditions.

[0032] Initiating event type is a classification in initiating event analysis based on how the initiating event affects the nuclear power plant. It is usually divided into a dozen to twenty different types, and the specific type is related to the reactor type.

[0033] The specific classification method mainly involves analyzing whether the integrity of the primary / secondary circuit boundaries, the systems performing accident mitigation functions, and their support systems are affected when the initiating event occurs. For example, if an emergency shutdown does not affect the integrity of the primary / secondary circuit boundaries or any mitigation systems, it is classified as a general transient initiating event. If the initiating event is caused by a rupture in the primary circuit piping, it is classified as a LOCA (Locally Occurring Complicated Event) initiating event because it affects the integrity of the primary circuit pressure boundary. Depending on the size and location of the rupture, the subsequent mitigation actions of the power plant will also differ, and LOCA initiating events will be further subdivided based on this.

[0034] It should be noted that this classification method is also a mature method already in use in the industry, and the type of initiating event is highly related to the heap type and system design.

[0035] Step 3: Calculate the average annual share for each operating condition.

[0036] This annual average share is used to calculate the annual average frequency of initiating events under different operating conditions. The specific calculation formula is as follows: ; ; ; In the above formula, F1, F2, and F3 are the annual average proportions of three operating conditions: full unit power operation, single module overhaul, and full unit overhaul, respectively; n is the number of modules in the high-temperature gas-cooled reactor nuclear power plant.

[0037] Step 4: Calculate the total annual average frequency of the initiating event.

[0038] The total annual average frequency of initiating events can be calculated using a variety of methods known in the art, including using general data, statistical estimation based on specific nuclear power plant operating data, fault tree modeling, and specific calculations.

[0039] In the PSA (Physical Safety Association) field, methods for calculating the frequency of initiating events other than statistical estimation and fault tree modeling are collectively referred to as specific calculations. There are two main specific calculation methods: one is to estimate the frequency of pipe ruptures by statistically analyzing the system's pipe length; the other is to assess the failure rate of specific equipment through reliability modeling and failure mechanism studies.

[0040] In practical implementation, system configurations may differ under different operating conditions, and these differences will be reflected in the fault tree model or specific calculations. If fault tree modeling and specific calculation methods are used to calculate the total annual average frequency of initiating events, modeling and calculation should be performed separately for the different system configurations under three operating conditions: full unit power operation, single module overhaul, and full unit overhaul. If other methods are used to calculate the total annual average frequency of initiating events, since these methods mainly rely on statistical data for calculation, and the data source generally provides the applicable operating conditions for the reference data, it is not necessary to perform separate modeling and calculations for different operating conditions.

[0041] Step 5: Calculate the annual average frequency of the initiating event under each operating condition.

[0042] The annual average frequency of the initiating event under each operating condition (full unit power operation, single module overhaul, and full unit overhaul) is calculated by multiplying the total annual average frequency of the initiating event by the annual average share of that operating condition to obtain the annual average frequency of the initiating event under that operating condition.

[0043] Step 6: Assess the impact of long-cycle overhauls on the frequency of initiating events.

[0044] The specific method is to substitute different overhaul cycles in step 3 to obtain the annual average share of each operating condition corresponding to different overhaul cycles; and further substitute into step 5 to obtain the annual average frequency of the initiating event under each operating condition corresponding to different overhaul cycles.

[0045] By comparing and analyzing the changes in the annual average frequency of initiating events corresponding to different overhaul cycles, and combining this with the actual operating characteristics of high-temperature gas-cooled reactor nuclear power plants, the analysis results show that they can more accurately reflect the actual operating characteristics of high-temperature gas-cooled reactor nuclear power plants, providing input for subsequent PSA modeling and risk quantification.

[0046] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. All contents not described in detail in the present invention can be derived from existing technologies.

Claims

1. A method for analyzing the impact of overhaul cycles on initiating events in a multi-module high-temperature gas-cooled reactor, characterized in that, The method includes: Step 1: Divide the operating conditions and determine the overhaul cycle and duration of overhaul for different operating conditions; Step 2: Use the FMEA method to identify the list of initiating events under different operating conditions; Step 3: Calculate the average annual share for each operating condition; Step 4: Calculate the total annual average frequency of the initiating event; Step 5: Calculate the annual average frequency of the initiating event under each operating condition.

2. The method for analyzing the impact of overhaul cycles on initiating events in a multi-module high-temperature gas-cooled reactor according to claim 1, characterized in that, The operating conditions include full unit power operation, single module overhaul, and full unit overhaul.

3. The method for analyzing the impact of overhaul cycles on initiating events in a multi-module high-temperature gas-cooled reactor according to claim 2, characterized in that, Step 2 includes: Step 2.1: List all systems within the analysis boundary of the high-temperature gas-cooled reactor nuclear power plant; Step 2.2: Based on the system functions and composition, analyze each failure mode and its failure impact under three operating conditions: full unit power operation, single module overhaul, and full unit overhaul. Step 2.3: Determine the failure impact of the failure mode and identify the initiating events under the three operating conditions; Step 2.4: Classify the initiating events to form a list of initiating events of different categories under the three operating conditions.

4. The method for analyzing the impact of overhaul cycles on initiating events in a multi-module high-temperature gas-cooled reactor according to claim 3, characterized in that, The method for determining the initiating event in step 2.3 is as follows: determine whether the failure effect of a specific failure mode of the system will cause one or more modules to trigger an emergency shutdown. If so, the emergency shutdown caused by the failure of the system is an initiating event.

5. The method for analyzing the impact of overhaul cycles on initiating events in a multi-module high-temperature gas-cooled reactor according to claim 4, characterized in that, In step 2.3, for different system configurations under three operating conditions—full unit power operation, single module overhaul, and full unit overhaul—the emergency shutdown caused by system failure under each of the three operating conditions is determined, and the initiation event under each of the three operating conditions is obtained.

6. The method for analyzing the impact of overhaul cycles on initiating events in a multi-module high-temperature gas-cooled reactor according to claim 5, characterized in that, In step 2.3, determining whether the failure impact of a specific failure mode of the system will cause one or more module stacks to trigger an emergency shutdown further includes: for different system configurations under three operating conditions—full unit power operation, single module overhaul, and full unit overhaul—determining which failure modes of the system will trigger an emergency shutdown of one or more module stacks under each of the three operating conditions, identifying which module stacks or modules will trigger the emergency shutdown, and determining the module stacks affected by the system failure.

7. The method for analyzing the impact of overhaul cycles on initiating events in a multi-module high-temperature gas-cooled reactor according to claim 3, characterized in that, Step 2.4 specifically involves classifying the identified initiating events according to their type and the number of affected modules, resulting in a series of single-module initiating events, dual-module initiating events, and multi-module initiating events, forming complete initiating event lists for the three operating conditions.

8. The method for analyzing the impact of overhaul cycles on initiating events in a multi-module high-temperature gas-cooled reactor according to claim 2, characterized in that, The formula for calculating the average annual share of each operating condition in step 3 is as follows: ； ； ； Among them, F1, F2, and F3 represent the annual average share of three operating conditions: full unit power operation, single module overhaul, and full unit overhaul, respectively; n represents the number of modules in the high-temperature gas-cooled reactor nuclear power plant; T cycle,m For single module overhaul cycle, T cycle,u For the overhaul cycle of the entire unit, T outage,m For single-module overhaul duration, T outage,u The duration of the overhaul of the entire unit.

9. The method for analyzing the impact of overhaul cycles on initiating events in a multi-module high-temperature gas-cooled reactor according to claim 2, characterized in that, The method for calculating the annual average frequency of the initiating event under each operating condition in step 5 is to multiply the total annual average frequency of the initiating event by the annual average share of the operating condition to obtain the annual average frequency of the initiating event under that operating condition.

10. The method for analyzing the impact of overhaul cycles on initiating events in a multi-module high-temperature gas-cooled reactor according to claim 2, characterized in that, The method further includes: Step 6: Evaluate the impact of long-cycle overhauls on the frequency of initiating events: Substitute different overhaul cycles into Step 3 to obtain the annual average share of each operating condition corresponding to different overhaul cycles; further substitute into Step 5 to obtain the annual average frequency of initiating events under each operating condition corresponding to different overhaul cycles.

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