Method and device for shortening refueling overhaul time of pebble bed high temperature gas cooled reactor

Abstract

The application discloses a method and device for shortening the refueling overhaul time of a pebble bed high-temperature gas cooled reactor, and relates to the technical field of fourth-generation nuclear reactor operation maintenance and nuclear safety supervision. The method comprises the following steps: constructing a probabilistic safety assessment model of the safety characteristics and shutdown conditions of the pebble bed high-temperature gas cooled reactor, and calculating the baseline risk value under each operating state; performing risk assessment on the maintenance, in-service inspection and supervision test according to the model and the baseline risk, and forming an optimization strategy; formulating a special risk acceptable criterion suitable for the reactor type, checking the risk increment of the optimization strategy, and establishing a relaxation rule for the state conversion of the overhaul; integrating the checked strategy and rule, forming an optimization scheme of the overhaul period, slowing down the decay of the short-lived fission products in the core by shortening the shutdown time, and completing the optimization of the overhaul period of the pebble bed high-temperature gas cooled reactor. Through multi-dimensional overhaul optimization and risk quantitative control, the application realizes the compression of the period and the division of the fuel area, and solves the problems of long overhaul and difficult identification of components.

Description

Technical Field

[0001] This invention relates to the field of fourth-generation nuclear reactor operation, maintenance and nuclear safety supervision technology, and in particular to a method and apparatus for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor. Background Technology

[0002] The pebble bed high-temperature gas-cooled reactor is one of the representative reactor types of fourth-generation advanced nuclear energy systems. It adopts fully ceramic-coated spherical fuel elements, helium coolant, and graphite moderation structure, possessing outstanding inherent safety characteristics. Under any credible accident condition, the maximum core temperature is still limited to below 1620°C, far below the melting point of the fuel elements and reactor internals materials (graphite), therefore, core meltdown is theoretically impossible.

[0003] However, existing pebble bed high-temperature gas-cooled reactors (such as the HTR-PM high-temperature gas-cooled reactor nuclear power plant demonstration project) have an initial overhaul time of over 90 days, significantly longer than the 25-35 days of traditional pressurized water reactor nuclear power units. This greatly reduces the economic competitiveness of this reactor type. The main reasons for this difference are threefold: First, the safety classification system is mismatched with the inherent safety of the reactor type. Equipment safety classification, periodic testing, and preventive maintenance are mainly based on the deterministic safety analysis standards for pressurized water reactors. Risk-guided safety classification methods have not yet been applied to high-temperature gas-cooled reactor overhauls, failing to fully leverage the inherent safety advantages of this reactor type. Second, there is insufficient operational experience with new equipment. Long-term operational data is lacking for unique equipment such as fuel loading and unloading systems, main helium blowers, and helium purification systems. Maintenance procedures are overly conservative, some test items are poorly designed, and there are still gaps in the technology and experience for overhauling primary loop radioactive equipment in high-temperature gas-cooled reactors. Third, there are numerous overhaul items and a dense critical path. A single refueling overhaul involves over two thousand items, including preventive maintenance, in-service inspections, and surveillance tests. Many activities are on the critical path, directly leading to extended project durations.

[0004] An excessively long overhaul period can also pose significant challenges to distinguishing between high- and low-enrichment fuels after reactor restart. Pebble bed high-temperature gas-cooled reactors employ an online continuous refueling mode, where both high-enrichment (e.g., 8.5%) and low-enrichment (e.g., 4.2%) fuel elements coexist within the reactor core during the transition core phase. After the overhaul and upon core restart, the fuel element loading and unloading system must use burnup measurement devices to perform online burnup measurements and distinguish between high and low enrichment levels for the fuel elements removed from the core, in order to identify the fuel element type and determine whether to return them to the core for reuse. During a reactor shutdown overhaul, the short-lived fission product zirconium-95 (half-life 64 days) within the core will continuously decay, gradually decreasing in quantity. When the overhaul duration exceeds 60 days, the decay activity of zirconium-95 becomes insufficient for distinguishing between high and low enrichment fuel elements, leading to difficulties in online differentiation. Therefore, shortening the overhaul period and reducing zirconium-95 decay during reactor shutdowns are the most direct and effective ways to alleviate the problem of distinguishing between high and low enrichment fuel elements from the source.

[0005] Risk-guided decision-making methods have gained widespread recognition and application in the international nuclear industry since the mid-1990s. Their core is to integrate the quantitative risk assessment capabilities of probabilistic safety analysis (PSA) onto traditional deterministic safety analysis, scientifically and rationally "loosening" overly conservative and unreasonable regulatory requirements. This improves operational flexibility and economy while ensuring that incremental risks meet reactor safety requirements. Currently, international nuclear reactor technology is developing towards diversification and higher efficiency, and the need for optimization and upgrading of new reactor types is increasingly urgent. Risk-guided technology, as a key means to improve the economy and safety of nuclear reactors, is seeing its application scenarios continuously expand.

[0006] my country's nuclear safety regulatory framework has laid a solid institutional foundation for the application of risk-guided technologies. Since its initial implementation at the Daya Bay Nuclear Power Plant in November 2022, the risk-guided operational technical specifications have been fully validated in daily unit operation and multiple refueling and overhauls. In November 2025, the China Nuclear Energy Association conducted its first peer review of the HTR-PM internal event probabilistic safety analysis work and compiled PSA assessment technical guidelines applicable to high-temperature gas-cooled reactors. The assessment concluded that the development and application of the high-temperature gas-cooled reactor PSA model has strong exploratory and pioneering characteristics, and its technical elements meet the requirements of the peer review guidelines, effectively supporting the implementation of risk-guided nuclear safety management measures. Internationally, PSA methodologies for high-temperature gas-cooled reactors are also continuously expanding, with methods such as dynamic Bayesian networks and global variance analysis of uncertainty being introduced to handle complex scenarios such as nuclear-non-nuclear system interactions.

[0007] Currently, the safety classification and maintenance requirements for high-temperature gas-cooled reactors (HTGRs) do not match their inherent safety characteristics, resulting in an excessive number of overhaul activities and excessively long overhaul periods. Excessive overhaul periods, in turn, lead to severe zirconium-95 decay in the reactor core, posing a challenge to online differentiation of high- and low-enrichment fuel elements shortly after restarting from an overhaul. Simultaneously, there is a lack of systematic risk-guided optimization methods for HTGR overhauls, as well as an integrated decision support system to support the engineering implementation of overhaul optimization schemes. There is an urgent need for a systematic overhaul optimization method and supporting system that can fully release the inherent safety margins of HTGRs and simultaneously address the challenges of shortening overhaul periods and resolving fuel differentiation issues. Summary of the Invention

[0008] The main objective of this invention is to provide a method for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor.

[0009] Another objective of this invention is to provide a device for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor.

[0010] The third objective of this invention is to provide an electronic device.

[0011] A fourth objective of this invention is to provide a non-transitory computer-readable storage medium.

[0012] To achieve the above objectives, a first aspect of the present invention proposes a method for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor, comprising:

[0013] A probabilistic safety assessment model was constructed to characterize the inherent safety characteristics and shutdown conditions of a pebble bed high-temperature gas-cooled reactor, and the baseline risk value of the reactor under different operating conditions was calculated. Based on the probabilistic safety evaluation model and the benchmark risk value, a risk quantification assessment is conducted on preventive maintenance activities, in-service inspection items, and supervision test cycles, and optimization strategies are generated based on the assessment results. Develop specific risk acceptance criteria for pebble bed type high-temperature gas-cooled reactors, use these criteria to verify the risk increment of optimization strategies, and establish rules for relaxing overhaul state transition restrictions. The validated optimization strategies and overhaul state transition restriction relaxation rules are integrated to form an overhaul duration optimization scheme. By shortening the downtime, the decay of short-lived fission products in the core is suppressed, thus optimizing the overhaul duration of the pebble bed type high-temperature gas-cooled reactor.

[0014] Optionally, a probabilistic safety assessment model characterizing the inherent safety characteristics and shutdown conditions of a pebble bed high-temperature gas-cooled reactor may be constructed, including: A core safety characteristic analysis model was built by combining the physical response characteristics and thermal-hydraulic operation laws of the pebble bed type high-temperature gas-cooled reactor core. The functional logic and failure modes of the helium purification system, fuel loading and unloading system, and passive waste heat removal system were analyzed, and corresponding failure logic models were constructed. A human behavior influence analysis model is introduced, and a model for verifying the rationality of the model is established to complete the construction of a multi-dimensional, all-factor probabilistic safety evaluation model.

[0015] Optionally, calculate the baseline risk value of the reactor under different operating conditions, including: Based on the probabilistic safety evaluation model, risk quantification calculations were performed under the full power operation condition of the reactor and under the normal shutdown condition of the reactor. The calculation results under two typical operating conditions are determined as the benchmark risk values ​​for the corresponding operating states, forming a benchmark reference system for comparing the risk increments before and after the overhaul optimization.

[0016] Optionally, based on the probabilistic safety evaluation model and the baseline risk value, a risk quantification assessment is performed on preventive maintenance activities, in-service inspection items, and surveillance test cycles. Based on the assessment results, optimization strategies are generated, including: Identify preventive maintenance tasks for target equipment during major overhauls, determine the risk level of maintenance activities by combining maintenance operation hours and equipment operational reliability data, demonstrate and extend the allowable withdrawal time of key equipment based on benchmark risk values, so that maintenance operations can be carried out online, and form a preventive maintenance optimization strategy. A risk-guided evaluation approach is adopted to classify the failure probability and consequences of key reactor equipment and systems, classify risk importance levels, optimize the allocation of in-service inspection resources, reduce the inspection frequency of low-risk components or convert them to condition monitoring, and form an optimization strategy for the in-service inspection outline. For safety-related monitoring and testing projects that occupy the critical path of major overhaul, based on operational experience data and equipment reliability parameters, we will conduct feasibility studies on extending the test cycle, reasonably extend the test execution cycle, and formulate a monitoring and testing cycle optimization strategy.

[0017] Optionally, specific risk acceptance criteria can be developed for pebble bed type high-temperature gas-cooled reactors, and these criteria can be used to verify the risk increment of optimization strategies, including: Based on the inherent safety characteristics and probabilistic safety assessment results of pebble bed type high-temperature gas-cooled reactors, an acceptable risk criterion for major overhauls adapted to pebble bed type high-temperature gas-cooled reactors is established. Based on the acceptable risk criteria for major overhaul projects, we will verify the risk increment after the implementation of strategies including preventive maintenance optimization, in-service inspection optimization, and supervision test cycle adjustment to ensure that the overall risk level is within an acceptable range after the implementation of various optimization measures.

[0018] Optionally, establish rules for relaxing overhaul status transition restrictions, including: To address the project delays caused by non-safety-critical equipment failures or failed tests during the unit startup phase at the end of the overhaul, a special risk assessment will be conducted and corresponding risk management measures will be developed. Under the premise of controllable risks, unit status transitions are allowed when low-risk equipment is temporarily unavailable, avoiding unplanned delays in the main overhaul process caused by abnormalities in a single pump, valve, instrument, or other equipment, thus forming an execution rule for relaxing status transition restrictions.

[0019] To achieve the above objectives, a second aspect of the present invention provides a device for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor, comprising: The model building module is used to build a probabilistic safety assessment model that characterizes the inherent safety characteristics and shutdown conditions of the pebble bed high-temperature gas-cooled reactor, and to calculate the baseline risk value of the reactor under different operating conditions. The risk assessment module is used to conduct a risk quantification assessment of preventive maintenance activities, in-service inspection items, and supervision test cycles based on the probabilistic safety evaluation model and the benchmark risk value, and generate optimization strategies based on the assessment results. The criteria development module is used to develop specific risk acceptable criteria for pebble bed type high temperature gas-cooled reactors, use these specific risk acceptable criteria to verify the risk increment of optimization strategies, and establish rules for relaxing overhaul state transition restrictions. The scheme integration module is used to integrate the verified optimization strategies and overhaul state transition restriction relaxation rules to form an overhaul period optimization scheme. By shortening the downtime, the decay of short-lived fission products in the core is suppressed, thus completing the overhaul period optimization of the pebble bed type high-temperature gas-cooled reactor.

[0020] Regarding the apparatus in the above embodiments, the specific manner in which each module performs its operation has been described in detail in the embodiments related to the method, and will not be elaborated upon here.

[0021] To achieve the above objectives, a third aspect of this application provides an electronic device, including a processor and a memory; wherein the processor reads executable program code stored in the memory to run a program corresponding to the executable program code, for implementing a method for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor as described in the first aspect embodiment.

[0022] To achieve the above objectives, the fourth aspect of this application proposes a non-transitory computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements a method for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor as described in the first aspect embodiment.

[0023] The embodiments of the present invention have the following beneficial effects: 1. By integrating online maintenance implementation, reducing in-service inspection items, extending the monitoring test cycle, and relaxing restrictions on overhaul status transition, the overhaul period for a single spherical bed high-temperature gas-cooled reactor can be reduced from the current 90 days to 35 days, significantly shortening the downtime and effectively making up for the shortcoming of the overhaul period of this reactor type, thus significantly improving its economic competitiveness with traditional pressurized water reactor nuclear power units.

[0024] 2. By shortening the overhaul period, the cumulative decay of zirconium-95 (half-life of 64 days), a short-lived fission product, can be directly reduced during reactor shutdown. Calculation and analysis have verified that when the overhaul period is reduced to less than 60 days, the burnup measurement system can accurately distinguish between high- and low-enrichment fuel elements online based on the decay activity of zirconium-95. This solves the technical bottleneck of fuel element differentiation in existing technologies from the source, ensuring the scientific nature of fuel element reuse decisions.

[0025] 3. Fully leverage the inherent safety advantages of pebble bed high-temperature gas-cooled reactors and reduce resource waste: Scientifically quantify the risk increment of various optimization measures through probabilistic safety analysis (PSA) modeling, and formulate specific risk acceptable criteria in combination with the inherent safety characteristics of the reactor type. This ensures that management requirements such as equipment safety classification, maintenance cycle, and test frequency are accurately matched with the actual safety level of the reactor, avoiding resource waste and performance loss caused by traditional overly conservative management models, and achieving a synergistic improvement in safety and economy.

[0026] 4. A complete methodology and technical system will be formed, from PSA model construction, risk assessment, optimization scheme design to effect evaluation. This system can not only be directly applied to the refueling and overhaul work of all subsequent pebble bed type high temperature gas-cooled reactor nuclear power plants, but also provide important technical references and engineering lessons for the overhaul optimization of other fourth-generation advanced nuclear reactor types, thus promoting the large-scale and efficient development of advanced nuclear energy technology. Attached Figure Description

[0027] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 A flowchart illustrating a method for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor, provided by an embodiment of the present invention; Figure 2 This is a structural diagram of a device for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor, provided in an embodiment of the present invention. Detailed Implementation

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0030] The following describes, with reference to the accompanying drawings, a method and apparatus for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor according to an embodiment of the present invention.

[0031] Example 1 This invention provides a method for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor. Figure 1 This is a schematic flowchart illustrating a method for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor provided in an embodiment of the present invention. Figure 1 As shown, the method includes the following steps: Step S1: Construct a probabilistic safety assessment model that characterizes the inherent safety characteristics and shutdown conditions of the pebble bed high-temperature gas-cooled reactor, and calculate the baseline risk value of the reactor under different operating conditions.

[0032] Specifically, the process of constructing the probabilistic safety assessment model in this application embodiment strictly follows the requirements of the Technical Guidelines for PSA Assessment of High-Temperature Gas-Cooled Reactors issued by the China Nuclear Energy Association, and adopts a first-level PSA modeling system, which specifically includes the construction of three core models: Firstly, regarding the core physics and thermal-hydraulic response model, this application uses a dedicated calculation program for high-temperature gas-cooled reactors as the core tool. Combining the core physics response characteristics and thermal-hydraulic operation laws of pebble-bed high-temperature gas-cooled reactors, a core safety characteristic analysis model is built. This model can accurately characterize the changes in key parameters such as temperature, power, and helium temperature / pressure under different scenarios including full-power operation, normal shutdown, and accident conditions. Its core calculation relationships can be expressed as follows:

[0033] in, Let P(t) be the core temperature at time t, and P(t) be the reactor power at time t. Let be the mass flow rate of helium coolant at time t. Let t be the helium inlet temperature. Let t be the reactor effective multiplication factor. This formula clarifies the quantitative correlation between core temperature and core operating parameters, providing a physical basis for subsequent risk calculations. Secondly, the system failure logic model. In this embodiment, a comprehensive analysis of the unique systems of the high-temperature gas-cooled reactor is conducted, including the helium purification system, the fuel loading and unloading system, and the passive residual heat removal system. By analyzing the functional configuration logic, equipment linkage relationship and typical failure modes of each system, a corresponding failure logic model is constructed. This model can characterize the impact path of single equipment failure and multi-equipment cascade failure on reactor safety. Third, the human factors analysis and model verification model are introduced in this application embodiment. The human factors behavior impact analysis model is introduced to consider the contribution of human factors such as operator error and emergency response delay to risk. At the same time, a model rationality verification model is established. By comparing the actual operation data with the model calculation results, the accuracy and applicability of the model are verified, and finally the multi-dimensional and all-factor probabilistic safety evaluation model is built.

[0034] After the probabilistic safety assessment model is constructed, risk benchmark calculations are carried out based on the model in this embodiment of the application. The specific process is as follows: using the constructed probabilistic safety assessment model as the basis for calculation, risk quantification calculations are carried out under the full-power operation condition of the reactor and under the normal shutdown condition of the reactor. Core risk indicators are introduced in the calculation process:

[0035] Where R is the total risk value, Let be the probability of the i-th accident sequence occurring. This represents the quantified severity of the consequences of the i-th accident sequence. In this embodiment, the failure probability of the core system and the severity of the accident consequences are quantified to obtain risk calculation results under two typical operating conditions. Subsequently, the calculation result under full-power operation is determined as the baseline risk value for full-power operation, and the calculation result under normal shutdown operation is determined as the baseline risk value for shutdown, forming a benchmark reference system for comparing risk increments before and after overhaul optimization. The formula for calculating the risk increment is:

[0036] in, To optimize the risk value, This serves as a benchmark risk value, providing a quantitative basis for risk assessment of subsequent optimization strategies.

[0037] Step S2: Based on the probabilistic safety evaluation model and the benchmark risk value, perform a risk quantification assessment of preventive maintenance activities, in-service inspection items, and supervision test cycles, and generate optimization strategies based on the assessment results.

[0038] In this embodiment, this step specifically involves generating optimization strategies across three dimensions. These three dimensions work synergistically and complement each other to jointly achieve the reduction of overhaul time and resource optimization, ensuring the comprehensiveness and reliability of the optimization effect: First, the preventive maintenance optimization strategy is generated. In this embodiment, the key preventive maintenance tasks to be performed during major overhauls are first identified, including emergency diesel generator sets, main helium blowers, control rod drive mechanisms, and key components of the fuel loading and unloading system. Combining the maintenance work hour requirements of each piece of equipment with equipment operational reliability data (such as Mean Time Between Failures (MTBF) and Time To Repair (MTTR), a standardized risk level assessment model is used to accurately determine the risk level of each maintenance activity. The model expression is:

[0039] in, Risk level, This represents the probability of equipment failure. The risk level of maintenance activities is determined by assessing the safety and economic losses caused by equipment failure.

[0040] Subsequently, based on the baseline risk value calculated by S1, the allowable withdrawal time (AOT) of critical equipment is demonstrated and extended. In this embodiment of the application, the upper limit of risk increment under the online maintenance implementation conditions is calculated to determine the reasonable extension range of AOT, ensuring that the extended AOT will not cause the overall risk to exceed the acceptable range.

[0041] Ultimately, through the aforementioned demonstration process, low- to medium-risk maintenance tasks that originally needed to be completed during reactor outages can now be implemented online, forming a complete preventative maintenance optimization strategy. This strategy can transfer some maintenance tasks to the full-power operation phase of the reactor core without occupying the outage period, directly reducing the operation time on the critical path of the outage, laying the foundation for shortening the outage period, while ensuring equipment maintenance quality and operational safety.

[0042] Second, the in-service inspection outline optimization strategy is generated. In this embodiment, a risk-guided evaluation method is adopted to classify the failure probability and consequences of key reactor equipment and systems (such as hot gas ducts, steam generators, pressure vessels, burnup measurement systems, and main helium blowers), and to categorize the risk importance levels. Specifically, this is achieved by constructing a risk importance evaluation matrix:

[0043] in, For high-risk, high-importance weighting, Low-risk, high-importance weighting High-risk, low-importance weighting Low-risk, low-importance weights.

[0044] During the matrix assignment process, each device is weighted based on its failure probability and the severity of its consequences. Then, according to the weight values, the devices are categorized into three types: high-risk critical equipment, medium-risk critical equipment, and low-risk high-margin equipment. High-risk critical equipment retains its original inspection frequency and standards; medium-risk critical equipment can have its inspection frequency appropriately reduced; and low-risk high-margin equipment can have its inspection frequency significantly reduced, or be converted to condition-based monitoring (i.e., replacing traditional downtime inspections with online monitoring and periodic patrols).

[0045] Based on the above classification results, the allocation of in-service inspection resources is optimized, and resources such as inspection manpower, equipment, and time are concentrated on high-risk critical equipment and systems, while reducing the inspection investment on low-risk, high-margin equipment. Risk demonstration is carried out through the probabilistic safety evaluation model constructed in step S1 to ensure that the failure risk of the equipment after inspection optimization is still within the acceptable range of the baseline risk value. Ultimately, this effectively reduces the total number of in-service inspection items for major overhauls, reduces the investment of overhaul resources and operation time, and further shortens the overhaul period.

[0046] Third, the strategy for optimizing the monitoring test cycle is generated. In this embodiment, for safety-related monitoring test items that occupy the critical path of major overhauls, such as tests on dedicated safety facility access routes and periodic tests of reactor protection systems, a feasibility study on extending the test cycle is conducted, combining feedback data from high-temperature gas-cooled reactor operation experience and equipment reliability parameters. During the study, a baseline risk value is used as a constraint to calculate the risk increment after extending the test cycle. When the following conditions are met: Extending the time determination period is feasible, among which This is the limit for risk increment.

[0047] After the feasibility study is approved, the execution cycle of the monitoring tests will be reasonably extended. For example, the dedicated safety facility passage test, which was originally carried out once every 12 months, will be extended to once every 18 months. Some non-critical monitoring tests that were originally required to be completed during the overhaul will be adjusted to be completed during the operation phase between two overhauls. Through such adjustments, the number of test items that need to be carried out during the overhaul will be reduced, the critical path time of the overhaul will be saved, and a complete monitoring test cycle optimization strategy will be formed. This strategy will work in conjunction with the optimization strategies for preventive maintenance and in-service inspection to further improve the overhaul time reduction effect.

[0048] Step S3: Develop specific risk acceptance criteria for pebble bed type high-temperature gas-cooled reactors, use these criteria to verify the risk increment of optimization strategies, and establish rules for relaxing overhaul state transition restrictions.

[0049] Specifically, the process of formulating a dedicated risk acceptable criterion in this application embodiment is as follows: Combining the inherent safety characteristics of the pebble bed high-temperature gas-cooled reactor, including the inherent safety characteristics of the reactor core, the characteristics of fission product release, and the fault tolerance characteristics of system failure, with the probabilistic safety assessment calculation results in S1, a special risk acceptable criterion for overhaul adapted to the pebble bed high-temperature gas-cooled reactor type is established. This criterion clarifies the risk increment limit corresponding to different types of optimization measures, such as the risk increment limit for preventive maintenance optimization. / year, risk increment limit for in-service inspection optimization ≤0.5×10 6 / year.

[0050] Subsequently, based on the acceptable risk criteria for this major overhaul project, the risk increments after implementing strategies such as preventive maintenance optimization, in-service inspection optimization, and monitoring test cycle adjustment were verified. The total risk value after implementing each strategy was calculated to ensure… Within an acceptable range, the formula is:

[0051] in, This represents the risk increment introduced by the i-th optimization measure, where i corresponds to different optimization categories, including the risk change brought about by individual measures such as preventive maintenance optimization, in-service inspection optimization, and adjustment of surveillance test cycle. This is the cumulative value of the risk increment of all optimization measures.

[0052] The verification process follows the principle of "individual items first, then overall": first, the cost of each optimization measure is calculated separately. Judge a single item Does it meet the corresponding individual risk increment limit? Then calculate. and ,judge Does it meet the total risk increment limit? If a certain strategy's... Exceeding the corresponding single-item limit, or If the total risk increment limit is exceeded, the scope or parameters of the strategy should be readjusted. For example, the range of equipment requiring online maintenance may be reduced, the frequency of inspections of low-risk components may be appropriately decreased, and the duration of the monitoring test cycle may be shortened. The calculation should be recalculated after the adjustment. and This continues until all individual risk increments and total risk increments meet the criteria, ensuring the safety and controllability of the optimization strategy and laying a safe foundation for the integration of subsequent optimization schemes.

[0053] In this embodiment, the process of establishing the relaxation rules for overhaul status transition is as follows: For the unit startup phase during the later stages of overhaul, a special risk assessment is conducted to address project delays caused by failures of non-critical safety equipment or failed tests. This assessment is also based on the probabilistic safety assessment model constructed in step S1, ensuring the accuracy and reliability of the assessment results and avoiding safety hazards caused by assessment bias. In this embodiment, by analyzing the failure probability and consequences of non-critical safety equipment (such as ordinary pumps and valves, auxiliary instruments, and secondary pipelines), and combining this with safety protection measures during unit startup, targeted supporting risk management measures are formulated. These include temporarily strengthening operational monitoring, adding temporary power supplies, adjusting operating limits, and assigning dedicated personnel for on-duty monitoring, ensuring timely handling of equipment abnormalities and guaranteeing safe unit startup.

[0054] Under the premise of controllable risk, this application embodiment allows unit status transition when low-risk equipment is in a short-term unavailability state. The duration of the short-term unavailability state is specified to be no more than 24 hours, and the aforementioned supporting risk management measures must be implemented to ensure that the short-term unavailability of equipment does not affect the safe performance of unit startup and does not cause the risk to exceed the acceptable range of the baseline risk value. This rule can effectively avoid unplanned delays of several hours to tens of hours in the main overhaul process caused by abnormalities in a single low-risk equipment such as a pump, valve, or instrument. For example, if a test of a common auxiliary pump fails, there is no need to wait for repairs to be completed before transitioning the unit status. The startup process can continue after implementing temporary monitoring measures, and repairs can be carried out after startup is completed, further shortening the total overhaul time and providing important support for reducing the overhaul period from 90 days to 35 days.

[0055] Step S4 integrates the verified optimization strategy and the overhaul state transition restriction relaxation rules to form an overhaul period optimization scheme. By shortening the downtime, the decay of short-lived fission products in the core is suppressed, thus completing the overhaul period optimization of the pebble bed type high-temperature gas-cooled reactor.

[0056] Specifically, the integration process in this embodiment is as follows: The preventive maintenance optimization strategy, in-service inspection outline optimization strategy, and monitoring test cycle optimization strategy verified through risk analysis in S2 are integrated with the overhaul status transition restriction relaxation rules established in S3. This process defines the implementing entities, implementation stages, resource allocation plans, and supporting risk control requirements for each optimization measure, forming a risk-guided optimization scheme for material replacement overhaul that covers the entire process and can be directly applied in engineering. This scheme not only includes specific optimization measures but also simultaneously clarifies the risk warning mechanism, anomaly handling procedures, and schedule control targets, ensuring the safe, efficient, and orderly progress of the overhaul implementation process.

[0057] The optimization scheme was then evaluated. In this embodiment, key indicators before and after implementation, including critical path duration, total project duration, number of high-risk operations, collective radiation dose, and zirconium-95 decay, were compared to quantitatively assess the overall benefits of the optimization scheme. The formula for calculating zirconium-95 decay is as follows:

[0058] in, The activity of zirconium-95 at time t. Initial activity, The decay constant is =64 days.

[0059] Calculations show that when the overhaul period is reduced from 90 days to less than 60 days, the decay of zirconium-95 can be controlled within the range that the burnup measurement system can accurately distinguish, ensuring the accurate differentiation of high and low enrichment fuel elements after restarting. At the same time, the implementation of the optimized scheme in the embodiments of this application verifies that the overhaul period of a single refueling reactor for a pebble bed type high-temperature gas-cooled reactor can be reduced from 90 days to 35 days, significantly improving the economic competitiveness of the reactor type and solving the problems of overhaul period optimization and fuel element differentiation.

[0060] In this embodiment, through the full implementation of the above S1 to S4 processes, a risk-guided decision-making system is deeply integrated into the entire process of refueling and overhauling a pebble bed high-temperature gas-cooled reactor, fully releasing the inherent safety margin of the reactor type and breaking through the time bottleneck caused by the overly conservative traditional maintenance model. The related methods not only effectively solve technical problems such as excessively long overhaul periods and mismatch between the safety classification system and reactor characteristics, but also simultaneously solve the engineering challenge of distinguishing between high and low enrichment fuel elements after overhaul restart. The complete technical route and implementation system formed in this application can be directly applied to the overhaul work of subsequent newly built pebble bed high-temperature gas-cooled reactor nuclear power plants, and can also provide important technical references and engineering lessons for the overhaul optimization, risk management, and operational procedure optimization of other fourth-generation advanced nuclear energy systems.

[0061] In the application of one embodiment of the present invention, the implementation process is as follows: Taking the steady-state operation of reactor 1 at 192 MWt in the High Temperature Gas-Cooled Reactor Demonstration Project (HTR-PM) as an example, the implementation of the method described in this invention will be explained in detail: Step 1: Establish a probabilistic safety assessment model for high-temperature gas-cooled reactors.

[0062] Based on the physical characteristics of high-temperature gas-cooled reactors (HTR-PMs), a probabilistic safety analysis (PSA) model was established using specialized software and strictly following the "Technical Guidelines for Peer Evaluation of Probabilistic Safety Analysis of High-Temperature Gas-Cooled Reactors" published by the China Nuclear Energy Association. The main modeling elements include: 1) Core Physical-Thermo-Hydraulic Model: The steady-state and transient response parameters of the core under various operating conditions calculated by dedicated physical-thermal programs for high-temperature gas-cooled reactors (such as VSOP, HUAKUN / VSOP, etc.) are transformed into analytical inputs for the PSA model accident sequence, establishing a mapping relationship between core state and safety function failure. The quantitative relationship of key core parameters satisfies:

[0063] in, Let t be the temperature of the reactor core region at time t. Let be the reactor power at time t. Let be the mass flow rate of helium coolant at time t. Let t be the helium inlet temperature. Let be the reactor's effective multiplication coefficient at time t.

[0064] 2) Dedicated safety facilities and support system logic diagram: accurately characterizes the functional configuration and failure logic of the dedicated safety systems of the high-temperature gas-cooled reactor (passive residual heat removal, steam generator accident discharge, secondary loop isolation, etc.); 3) Shutdown Condition Modeling: For reactors in specific configuration states during major overhauls, such as depressurization, partial system disconnection, and fuel loading and unloading system maintenance, establish a shutdown condition event tree and fault tree to identify important initiating events and mitigation sequences under shutdown conditions; 4) Human Factors Reliability Analysis Model: Combining the characteristics of pebble bed reactor shutdown overhaul operations, and based on operational experience feedback and simulator data, a quantitative assessment of the probability of human error in key operations (such as system isolation, test operations, etc.) during the overhaul is conducted. 5) Model verification and validation: Using HTR-PM startup test data (including control rod value measurement, zero-power physics test, and power-up test) and historical operation data, the key parameters of the model are compared and verified to ensure that the deviation between the calculated values ​​and the measured values ​​is within an acceptable range.

[0065] Step 2: Risk benchmark calculation.

[0066] Based on the HTR-PM internal event PSA model established in step 1, the baseline risk values ​​of the reactor under full-power operation, low-power operation, and reactor shutdown / refueling conditions are calculated respectively. The total risk value is calculated according to the following:

[0067] in, The total risk value, Let be the probability of the i-th accident sequence occurring. Let be the quantified severity value of the consequences of the i-th accident sequence. Based on this, the baseline risk for each operating condition is obtained, serving as a benchmark for comparing the risk increment of subsequent overhaul optimization measures. 1) Full-power operation: reference core damage frequency The frequency of large-scale releases of radioactive materials in the early stages of the baseline. ; 2) Refueling and Outage Status: Core Damage Probability under Baseline Conditions .

[0068] Risk increment calculation uniformly adopts:

[0069] in, To optimize the risk value, This is the baseline risk value for the corresponding operating condition.

[0070] Step 3: Extend the time-to-operation (AOT) of some equipment to enable online maintenance.

[0071] Identify preventative maintenance activities that must be completed during the reactor outage overhaul. The risk level of these maintenance activities is determined using the following method:

[0072] in, Risk level, This represents the probability of equipment failure. This represents the safety and economic losses caused by equipment failure.

[0073] After classification, AOT optimization will be carried out focusing on the equipment shown in Table 1: Table 1

[0074] Taking an emergency diesel generator set as an example, the PSA model sets up the "EDG_AOT_14d" task to simulate extending the AOT (Availability Time) of one EDG from 3 days to 14 days. During this period, if a loss of external power supply occurs, another EDG will assume the emergency power supply function. Calculations show that... , .

[0075] The above risk increments meet the specific risk acceptable criteria ( After implementing this step, preventative maintenance of the above-mentioned equipment can be shifted from the overhaul period to online operation during power operation, saving approximately 8 days of critical path time per overhaul.

[0076] Step 4: Optimize the in-service inspection outline and reduce the total number of overhaul items.

[0077] For equipment and systems unique to high-temperature gas-cooled reactors, a risk-guided in-service inspection method is adopted, and a risk importance assessment matrix is ​​constructed based on the probability of component failure and the severity of the consequences of failure.

[0078] in, For high-risk, high-importance weighting, Low-risk, high-importance weighting High-risk, low-importance weighting Low-risk, low-importance weights.

[0079] Based on the weight classification, inspection resources are focused on high-risk areas, significantly reducing the inspection frequency of low-risk and high-margin equipment or converting it to status monitoring. The key equipment optimization scheme is shown in Table 2.

[0080] Table 2

[0081] Based on the sensitivity analysis using the PSA model, as shown in Table 2, the cumulative increase in core damage frequency due to adjustments in inspection frequency is as follows. The increase in risk is negligible. This step saves approximately 12 days of critical path time during major overhauls.

[0082] Step 5: Extend the monitoring test cycle and reduce the number of major overhaul test items.

[0083] For monitoring test projects that occupy the critical path of major overhauls, based on feedback from high-temperature gas-cooled reactor operation experience and equipment reliability data, a feasibility study on extending the test cycle is conducted, with the following criteria:

[0084] in, This represents the increased risk resulting from the extended testing period. This is the limit for risk increment. Specific optimization schemes are shown in Table 3.

[0085] Table 3

[0086] Taking the dedicated safety facility passage test in Table 3 as an example, the test cycle is extended from every one material change cycle to every two material change cycles, corresponding to... This step saves approximately 5.5 days of critical path time during major overhauls.

[0087] Step 6: Develop rules to relax overhaul status transition restrictions and reduce unplanned delays.

[0088] To address situations where non-safety-critical equipment becomes unavailable or fails tests during the unit startup phase at the end of a major overhaul, a risk assessment and management procedure for state transitions has been established. This procedure allows for the temporary acceptance of short-term unavailability of some low-risk equipment, provided the risk is manageable, and state transitions can continue. An example of the rule framework is as follows: 1) Applicable objects: Equipment with a safety level of D or E, or equipment that is safety-related but is in a redundant configuration and whose unavailability time is far below the backoff time limit; 2) Risk assessment: The temporary ICCDP value under the current unavailable configuration of the device is calculated in real time using the state transition risk assessment subsystem and compared with the dedicated criteria; 3) Risk management actions: such as temporarily strengthening operational monitoring, allocating additional temporary power supplies / backup equipment, adjusting operational limits, and developing emergency response plans; 4) Decision-making authorization: Based on the level of risk, authorization is granted by the shift leader, deputy general manager of operations, or nuclear safety committee at different levels.

[0089] Application examples: During the later stages of this overhaul (day 42), the unit had completed core loading and primary loop pressurization and warm-up, preparing for critical operation. One non-safety-grade helium purification compressor (Class D equipment) was unable to be put into operation due to a controller model failure. The state transition risk assessment subsystem quickly calculated that the compressor's unavailability reduced the dedicated safety facility's logical redundancy from "2 / 3" to "1 / 3," but the unit was in a low-power warm-up phase with an expected repair time of only 4 hours. Temporary... Far below the criterion threshold The operations decision-making team approved the continuation of the status transition in accordance with the rules, and took the following risk management actions: (1) arranged for instrumentation personnel to prioritize repairs; (2) strengthened the status monitoring of the other two compressors; and (3) developed an emergency response plan. This operation avoided an unplanned delay of approximately 8 hours for the overhaul.

[0090] Step 7: Develop specific risk acceptance criteria for high-temperature gas-cooled reactors.

[0091] Based on the inherent safety characteristics of high-temperature gas-cooled reactors (core meltdown is physically impossible, fission products are multi-layered, and long-term passive cooling is possible after an accident) and the quantitative results of the PSA model established in steps 1-2, a risk acceptance criterion specifically for fourth-generation high-temperature gas-cooled reactors is formulated. The optimized total risk satisfies the following:

[0092] in, For the risk increment of the i-th optimization measure, This represents the total risk increment. The specific criteria are shown in Table 4.

[0093] Table 4

[0094] The risk increment limits for individual optimization measures are as follows: Preventive maintenance optimization Optimization of in-service inspection .

[0095] Basis for formulation: 1) High-temperature gas-cooled reactor reference CDF (~10 -8 / reactor-year) compared to pressurized water reactors (~10 -5 The risk increment threshold is about three orders of magnitude lower than that of the annual stack, and the threshold for accepting risk increments can be appropriately relaxed while maintaining a sufficiently small risk level. 2) High-temperature gas-cooled reactor accidents progress slowly (hours to days), and the probability of successful human intervention is significantly higher than that of pressurized water reactors; 3) Multi-layer coated particulate fuel elements have an extremely strong ability to retain fission products, and the early release frequency benchmark value is already extremely low.

[0096] Step 8: Integration and effect evaluation of the overhaul schedule optimization plan.

[0097] Based on the current HTR-PM unit's refueling overhaul network plan of approximately 50 days after initial optimization, the optimization measures in steps 3-6, which have undergone risk assessment, are integrated into a complete risk-guided optimization scheme for refueling overhaul. The main contents are shown in Table 5.

[0098] Table 5

[0099] The optimization measures shown in Table 5 were input into the scheme integration and schedule simulation subsystem of the overhaul optimization decision support system. Using the original 50-day overhaul network plan as the baseline, the critical path was recalculated. After optimization, the total duration of the critical path was reduced from 49.5 days to 34.8 days, with a schedule reduction rate of approximately 29.7%. It is recommended that the overhaul schedule be arranged for 35 days.

[0100] Quantitative assessment of the effect of distinguishing between high and low enrichment fuels: Zirconium-95 decays according to the laws of radioactive decay:

[0101] in, The activity of zirconium-95 at time t. Initial activity, Tianwei Zirconium-95 half-life.

[0102] The average core burnup before the overhaul was 22,000 MWd / tU. The shutdown time was set to 50 days (baseline) and 35 days (optimized). The fuel differentiation effect evaluation model was used to calculate the total activity of residual zirconium-95 in the core and the signal-to-noise ratio of γ-scan of fuel elements. The results are shown in Table 6.

[0103] Table 6

[0104] Overall Benefits Summary: This embodiment verifies the technical feasibility, risk acceptability, and significant benefits of the method of the present invention in optimizing refueling overhauls of high-temperature gas-cooled reactors. A single overhaul of a single HTR-PM unit can reduce the construction period by approximately 30% (50 days → 35 days), increasing power generation revenue by approximately 31 million yuan (calculated based on a grid-connected electricity price of 0.43 yuan / kWh). Simultaneously, it significantly improves fuel operating conditions and reduces personnel radiation dose by approximately 25%, achieving a dual improvement in both economic efficiency and safety.

[0105] Example 2 This invention provides a device for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor. Figure 2 This is a schematic diagram of a device for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor, provided in an embodiment of the present invention. Figure 2 As shown, the device includes: The model building module 100 is used to build a probabilistic safety evaluation model that characterizes the inherent safety characteristics and shutdown conditions of the pebble bed high-temperature gas-cooled reactor, and to calculate the baseline risk value of the reactor under different operating conditions. The risk assessment module 200 is used to conduct a risk quantification assessment of preventive maintenance activities, in-service inspection items and supervision test cycles based on the probabilistic safety evaluation model and the benchmark risk value, and generate optimization strategies based on the assessment results. The criteria development module 300 is used to develop specific risk acceptable criteria for pebble bed type high temperature gas-cooled reactors, to verify the risk increment of optimization strategies using specific risk acceptable criteria, and to establish rules for relaxing overhaul state transition restrictions. The solution integration module 400 is used to integrate the verified optimization strategies and overhaul state transition restriction relaxation rules to form an overhaul period optimization scheme. By shortening the downtime, the decay of short-lived fission products in the core is suppressed, thus completing the overhaul period optimization of the pebble bed type high-temperature gas-cooled reactor.

[0106] Regarding the apparatus in the above embodiments, the specific manner in which each module performs its operation has been described in detail in the embodiments related to the method, and will not be elaborated upon here.

[0107] Example 3 To implement the methods of the above embodiments, the present invention also provides an electronic device, which includes a memory and a processor; wherein the processor reads executable program code stored in the memory to run a program corresponding to the executable program code, so as to implement the various steps of the methods described above.

[0108] Example 4 To implement the above embodiments, this application also proposes a non-transitory computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the method described in the foregoing embodiments.

[0109] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0110] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0111] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

Claims

1. A method for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor, characterized in that, include: A probabilistic safety assessment model was constructed to characterize the inherent safety characteristics and shutdown conditions of a pebble bed high-temperature gas-cooled reactor, and the baseline risk value of the reactor under different operating conditions was calculated. Based on the probabilistic safety evaluation model and the benchmark risk value, a risk quantification assessment is conducted on preventive maintenance activities, in-service inspection items, and supervision test cycles, and optimization strategies are generated based on the assessment results. Develop specific risk acceptance criteria for pebble bed type high-temperature gas-cooled reactors, use these criteria to verify the risk increment of optimization strategies, and establish rules for relaxing overhaul state transition restrictions. The validated optimization strategies and overhaul state transition restriction relaxation rules are integrated to form an overhaul duration optimization scheme. By shortening the downtime, the decay of short-lived fission products in the core is suppressed, thus optimizing the overhaul duration of the pebble bed type high-temperature gas-cooled reactor.

2. The method according to claim 1, characterized in that, A probabilistic safety assessment model characterizing the inherent safety characteristics and shutdown conditions of a pebble bed high-temperature gas-cooled reactor is constructed, including: A core safety characteristic analysis model was built by combining the physical response characteristics and thermal-hydraulic operation laws of the pebble bed type high-temperature gas-cooled reactor core. The functional logic and failure modes of the helium purification system, fuel loading and unloading system, and passive waste heat removal system were analyzed, and corresponding failure logic models were constructed. A human behavior influence analysis model is introduced, and a model for verifying the rationality of the model is established to complete the construction of a multi-dimensional, all-factor probabilistic safety evaluation model.

3. The method according to claim 2, characterized in that, Calculate the baseline risk value of the reactor under different operating conditions, including: Based on the probabilistic safety evaluation model, risk quantification calculations were performed under the full power operation condition of the reactor and under the normal shutdown condition of the reactor. The calculation results under two typical operating conditions are determined as the benchmark risk values ​​for the corresponding operating states, forming a benchmark reference system for comparing the risk increments before and after the overhaul optimization.

4. The method according to claim 3, characterized in that, Based on the probabilistic safety evaluation model and the baseline risk value, a risk quantification assessment is conducted on preventive maintenance activities, in-service inspection items, and surveillance test cycles. Based on the assessment results, optimization strategies are generated, including: Identify preventive maintenance tasks for target equipment during major overhauls, determine the risk level of maintenance activities by combining maintenance operation hours and equipment operational reliability data, demonstrate and extend the allowable withdrawal time of key equipment based on benchmark risk values, so that maintenance operations can be carried out online, and form a preventive maintenance optimization strategy. A risk-guided evaluation approach is adopted to classify the failure probability and consequences of key reactor equipment and systems, classify risk importance levels, optimize the allocation of in-service inspection resources, reduce the inspection frequency of low-risk components or convert them to condition monitoring, and form an optimization strategy for the in-service inspection outline. For safety-related monitoring and testing projects that occupy the critical path of major overhaul, based on operational experience data and equipment reliability parameters, we will conduct feasibility studies on extending the test cycle, reasonably extend the test execution cycle, and formulate a monitoring and testing cycle optimization strategy.

5. The method according to claim 4, characterized in that, Develop specific risk acceptance criteria for pebble bed high-temperature gas-cooled reactors, and use these criteria to validate the risk increment of optimization strategies, including: Based on the inherent safety characteristics and probabilistic safety assessment results of pebble bed type high-temperature gas-cooled reactors, an acceptable risk criterion for major overhauls adapted to pebble bed type high-temperature gas-cooled reactors is established. Based on the acceptable risk criteria for major overhaul projects, we will verify the risk increment after the implementation of strategies including preventive maintenance optimization, in-service inspection optimization, and supervision test cycle adjustment to ensure that the overall risk level is within an acceptable range after the implementation of various optimization measures.

6. The method according to claim 5, characterized in that, Establish rules for relaxing restrictions on overhaul status transitions, including: To address the project delays caused by non-safety-critical equipment failures or failed tests during the unit startup phase at the end of the overhaul, a special risk assessment will be conducted and corresponding risk management measures will be developed. Under the premise of controllable risks, unit status transitions are allowed when low-risk equipment is temporarily unavailable, avoiding unplanned delays in the main overhaul process caused by abnormalities in a single pump, valve, instrument, or other equipment, thus forming an execution rule for relaxing status transition restrictions.

7. A device for shortening the refueling and overhaul time of a pebble bed type high-temperature gas-cooled reactor, characterized in that, include: The model building module is used to build a probabilistic safety assessment model that characterizes the inherent safety characteristics and shutdown conditions of the pebble bed high-temperature gas-cooled reactor, and to calculate the baseline risk value of the reactor under different operating conditions. The risk assessment module is used to conduct a risk quantification assessment of preventive maintenance activities, in-service inspection items, and supervision test cycles based on the probabilistic safety evaluation model and the benchmark risk value, and generate optimization strategies based on the assessment results. The criteria development module is used to develop specific risk acceptable criteria for pebble bed type high temperature gas-cooled reactors, use these specific risk acceptable criteria to verify the risk increment of optimization strategies, and establish rules for relaxing overhaul state transition restrictions. The scheme integration module is used to integrate the verified optimization strategies and overhaul state transition restriction relaxation rules to form an overhaul period optimization scheme. By shortening the downtime, the decay of short-lived fission products in the core is suppressed, thus completing the overhaul period optimization of the pebble bed type high-temperature gas-cooled reactor.

8. The apparatus according to claim 7, characterized in that, The risk assessment module is also used for: Identify preventive maintenance tasks for target equipment during major overhauls, determine the risk level of maintenance activities by combining maintenance operation hours and equipment operational reliability data, demonstrate and extend the allowable withdrawal time of key equipment based on benchmark risk values, so that maintenance operations can be carried out online, and form a preventive maintenance optimization strategy. A risk-guided evaluation approach is adopted to classify the failure probability and consequences of key reactor equipment and systems, classify risk importance levels, optimize the allocation of in-service inspection resources, reduce the inspection frequency of low-risk components or convert them to condition monitoring, and form an optimization strategy for the in-service inspection outline. For safety-related monitoring and testing projects that occupy the critical path of major overhaul, based on operational experience data and equipment reliability parameters, we will conduct feasibility studies on extending the test cycle, reasonably extend the test execution cycle, and formulate a monitoring and testing cycle optimization strategy.

9. An electronic device, characterized in that, Including processor and memory; The processor reads executable program code stored in the memory to run a program corresponding to the executable program code, so as to implement the method as described in any one of claims 1-6.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1-6.

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