Method and system for selecting solid-state micro-stack design benchmark accident

Abstract

The invention discloses a method for selecting a solid-state micro-heap design benchmark accident. The method comprises the following steps of: establishing an event tree and calculating the occurrence frequency of an event sequence according to an originating event list and a corresponding occurrence frequency; obtaining a solid-state micro-stack design reference event; and providing a key safety function list and a PSA modeling system, taking a system which is used as an accident consequence relieving system in all design reference events as a safety related system, and screening out a design reference event which is successfully executed by the safety related system as a design reference accident of the solid-state micro-reactor. According to the method, the structural design characteristics of the solid-state micro-reactor can be effectively analyzed based on risk guidance, design basis accidents are reasonably screened out, and the safety management level of the solid-state micro-reactor is effectively improved. The invention further provides a system for selecting the solid-state micro-reactor design benchmark accident.

Description

Technical Field

[0001] The invention belongs to the field of nuclear power, and in particular relates to a method and system for selecting a design basis accident of a solid-state micro-reactor. Background Art

[0002] Design basis accidents (DBA) are a set of representative accident scenarios that can impact the safety of nuclear power plants. By conducting safety analysis on nuclear power plants based on design basis accidents and comparing their consequences with determined design criteria, it is possible to evaluate whether the nuclear power plants meet safety requirements.

[0003] For pressurized water reactor nuclear power plants, a relatively mature and complete design basis accident system has been established based on the probabilistic safety assessment (PSA) analysis framework and risk criteria. From the perspective of avoiding radioactive hazards, if the pressurized water reactor nuclear power plant can ensure the realization of the five safety functions of reactivity control, reactor pressure control, reactor coolant load control, core decay heat removal and containment integrity, the safety of the nuclear power plant can be considered reliable.

[0004] However, as a new type of reactor, the structure and principle of solid-state micro-reactors are significantly different from those of traditional pressurized water reactors. For example, solid-state micro-reactors do not have a liquid primary coolant, but rely on conduction and radiation between solid metals to remove heat. Due to these differences, the existing pressurized water reactor design basis accidents are not of sufficient significance for the system safety classification and safety management guidance of solid-state micro-reactors. Therefore, providing a method for selecting design basis accidents based on the structural characteristics of solid-state micro-reactors is of positive significance for improving the safety level of solid-state micro-reactors. Summary of the invention

[0005] The purpose of the present invention is to provide a method for selecting a design basis accident of a solid-state micro-reactor to improve the safety management level of the solid-state micro-reactor. The present invention also provides a system for selecting a design basis accident of a solid-state micro-reactor.

[0006] According to an embodiment of one aspect of the present invention, a method for selecting a solid-state micro-reactor design basis accident is provided, the method comprising the following steps:

[0007] Step a): providing a list of solid-state micro-reactor initiating events and the occurrence frequencies of corresponding initiating events;

[0008] Step b): providing a system for critical safety function list and PSA modeling, establishing an event tree according to the initiating event list, obtaining an event sequence corresponding to the initiating event, and obtaining the occurrence frequency of the event sequence;

[0009] Step c): obtaining a solid-state micro-reactor design basis event based on the frequency of the event sequence and a given event sequence frequency limit;

[0010] Step d): Screening out systems that serve as accident consequence mitigation systems in all the solid-state micro-reactor design basis events as safety-related systems;

[0011] Step e): Screening out the design basis events in which only the safety-related systems are successfully executed as solid-state micro-reactor design basis accidents.

[0012] The above method can combine the design characteristics of solid-state micro-reactors, reasonably select the design basis accidents of solid-state micro-reactors based on risk guidance, and improve the safety management level of solid-state micro-reactors.

[0013] Furthermore, in some embodiments, in the step a), the initiating event is obtained through a failure mode and effects analysis method.

[0014] Furthermore, in some embodiments, the initiating events in step a) include accidental shutdown, general transient, transient overpower, failure of a small number of heat pipes, failure of a large number of heat pipes, accidental opening of residual exhaust valves and failure of core matrix.

[0015] Furthermore, in some embodiments, the key safety functions in the key safety function list in step b) include reactivity control, decay heat removal and radioactive containment.

[0016] Furthermore, in some embodiments, the event tree in step b) is constructed by determining the system responses required to mitigate the consequences of each of the initiating events.

[0017] Furthermore, in some embodiments, the probabilities of success and failure of the event tree branches in step b) are calculated using a fault tree.

[0018] Further, in some embodiments, the frequency of the solid-state micro-reactor design basis event in step c) is 10 -4 / Pile-year-10 -2 / pile years.

[0019] Furthermore, in some embodiments, the safety-related systems in step d) include an emergency shutdown system, a residual heat removal system, and a chamber system.

[0020] According to another embodiment of the present invention, a system for selecting a solid-state micro-reactor design basis accident is provided, the system comprising a memory and a processor. The memory stores a calculation program, and when the calculation program is executed by the processor, the method for selecting a solid-state micro-reactor design basis accident provided in any of the above embodiments can be implemented. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a flow chart of a method for selecting a solid-state micro-reactor design basis accident in an embodiment;

[0022] Figure 2 A schematic diagram of a solid-state micro-pile event tree in an embodiment;

[0023] Figure 3 It is a schematic diagram of selecting a solid-state micro-reactor design basis accident process in an event tree in one embodiment.

[0024] The purpose of the above drawings is to explain the present invention in detail so that those skilled in the art can understand the technical concept of the present invention, but it is not intended to limit the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0026] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The phrase appearing in various locations in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments herein may be combined with other embodiments without causing structural conflicts.

[0027] In the description herein, "plurality" means at least two.

[0028] As a new type of reactor, the structure and principle of solid-state micro-reactor are quite different from those of pressurized water reactors and fast reactors. Solid-state micro-reactors mainly use heat pipes to directly remove heat from the reactor core through conduction and radiation between solid metals, thereby omitting the complex liquid primary coolant system in pressurized water reactors, achieving structural simplification and improving the inherent safety of the reactor. Therefore, solid-state micro-reactors do not have the risk of heat transfer deterioration caused by deviation from nucleate boiling (DNB) in pressurized water reactors. Also because of this structural difference, the more traditional and mature design basis accident (DBA) schemes and safety function design requirements applicable to pressurized water reactors cannot be applied to solid-state micro-reactors.

[0029] For pressurized water reactors, from the perspective of avoiding radioactive hazards, if the design can ensure the realization of five safety functions: reactivity control, reactor pressure control, reactor coolant loading control, core decay heat removal, and containment integrity, the safety of the nuclear power plant can be considered to be guaranteed. However, for solid-state micro-reactors, there are no safety functions for reactor pressure control and reactor coolant loading, and the systems used to perform safety functions in solid-state micro-reactors are also very different from those in pressurized water reactors.

[0030] In order to solve the above problems, an embodiment of one aspect of the present invention provides a method for selecting design basis accidents of solid-state micro-reactors, which uses a probabilistic safety assessment (PSA) tool based on risk-guided design to carry out initiating event analysis, event sequence analysis, system analysis and quantitative calculation of event sequence frequency, thereby obtaining design basis events and screening safety-related systems, so as to reasonably select design basis accidents of solid-state micro-reactors, reduce the processing requirements for safety-related but low safety importance levels of structures, systems and components (SSCs), strengthen the attention to non-safety-related but high safety importance levels of SSCs, optimize resources while improving the safety level of solid-state micro-reactors.

[0031] like Figure 1 As shown, the method comprises the following steps:

[0032] Step a): providing a list of solid-state micro-reactor initiating events and the occurrence frequencies of the corresponding initiating events.

[0033] Among them, each initiating event in the initiating event list is obtained by failure mode and effects analysis (FMEA) method, and the initiating events with similar radioactive consequences are grouped.

[0034] In one embodiment, combined with the design features of the solid-state micro-reactor, it is determined that: the initiating event related to the failure of the heat pipe will lead to the loss of the core heat removal function, which is sufficient to trigger an emergency shutdown; the initiating event of the core matrix failure due to manufacturing defects, reactor operating conditions and other factors will lead to the separation of fuel and heat pipes, the failure of the core heat removal function, and trigger an emergency shutdown; based on the drum structure of the solid-state micro-reactor, the transient overpower initiating event caused by the introduction of reactivity due to the drum misalignment or the wrong shutdown initiating event caused by the drum malfunction, etc. A total of seven initiating events are determined, including wrong shutdown (SSR), general transient (GTRAN), transient overpower (TOP), small amount of heat pipe failure (LSOHP), large amount of heat pipe failure (LLOHP), residual exhaust valve mis-opening (SPJNA) and core matrix failure (COR). The frequency of the initiating event can be obtained through existing general data, empirical data and other methods. Among them, LSOHP and LLOHP can be specifically defined according to the specific design of the solid-state micro-reactor to be analyzed, such as the model and structure.

[0035] Step b): Provide a critical safety function list and a PSA modeling system, establish an event tree according to the initiating event list, obtain the event sequence corresponding to the initiating event, and obtain the occurrence frequency of the event sequence.

[0036] Different from the key safety functions of pressurized water reactors, solid-state micro-reactors use a solid core combined with a heat pipe thermal conduction design and operate under normal pressure conditions. The key safety functions of solid-state micro-reactors include reactivity control, decay heat removal and radioactive containment.

[0037] In one embodiment, the event tree is constructed by determining the system response required to mitigate the initiating event, and the system that performs the key safety function is identified according to the design characteristics of the solid-state micro-reactor. Since the solid-state micro-reactor does not have a liquid primary coolant in its design, it does not have the safety injection system and pressure relief system of the pressurized water reactor. Instead, it realizes the reactivity control and shutdown functions through the emergency shutdown system and the drum control system; the residual heat removal system can realize the core decay heat removal function through heat conduction of heat pipes and air convection heat exchange; the chamber system provides the overall radioactive containment function.

[0038] Therefore, the three key safety functions of the heat pipe micro-reactor correspond to four systems that require probabilistic safety assessment modeling: the reactivity control function corresponds to the emergency shutdown system (ROD), the drum control system (DMS), the decay heat removal corresponds to the residual heat removal system (JNA) and the radioactive containment corresponds to the compartment system (CS).

[0039] The event tree-fault tree model is used for analysis.

[0040] In one embodiment, the event tree model is as follows: Figure 2 As shown in the figure, the top layer of the event tree is a series of responses to events listed in order (such as systems that perform key safety functions). Enter the event tree starting from a certain initiating event (such as LSOHP), and determine whether the consequences of the initiating event are mitigated (whether the system successfully performs the function) at each branch node. If the mitigation is successful, enter the upward branch, and if the mitigation fails, enter the downward branch. In the event tree, RDD, DMS, JNA, and CS have branches, and judgments are made at each branch node in turn. Each complete path represents a test piece sequence. Taking LSOHP as the initiating event, a total of 16 event sequences LSOHP:0001-LSOHP:0016 can be obtained.

[0041] In order to determine the probability of success and failure of each branch of the event tree, a fault tree is used to perform failure analysis on each system. The fault tree itself is a graphical model of fault series and parallel, which represents the logical relationship between the top event of the fault tree and various failure events that lead to system failure. In one embodiment, according to the design characteristics and success criteria of the solid-state micro-reactor, a fault tree logic structure is constructed: for the top event of DMS failure, when the number of drums successfully reset is less than a given number (for example, there are not less than two drums that cannot be reset), it is determined that the top event occurs; for DMS failure, it may be caused by the failure of the drum drive mechanism or the failure of the instrumentation and control system to trigger the shutdown, that is, the DMS failure is connected by the above two direct cause events with an "OR" logic gate; for the drive failure event of the drum drive mechanism, it may be caused by two or more drum drive mechanism operation failures or common cause failures (bottom-level basic events), that is, the drive failure of the drum drive mechanism is connected by the two direct cause events with an "OR" logic gate; and if two or more drum drive mechanisms fail to operate, they are connected by the "K / N" logic gate and the direct cause events of each drum drive mechanism operation failure (bottom-level basic event). According to the same method, the actual situation of the system is expanded layer by layer until all direct cause events are bottom-level basic events, and finally the occurrence of the top event is converted into Boolean algebra between all bottom-level basic events. Based on the failure data such as the hardware failure probability of each component and the probability of human error, the probability of occurrence of each basic event at the bottom of the fault tree can be calculated, and the probability of occurrence of the top event can be obtained by using the minimum cut set quantification technology. Combining the frequency of the initiating event and the probability of failure (or success) of the mitigation system, the frequency of occurrence of each event sequence in the event tree can be obtained.

[0042] Step c): According to the frequency of the event sequence, the solid-state micro-reactor design basis event is obtained based on the event sequence frequency limit given by the risk guidance.

[0043] For the seven types of initiating events in step a), the corresponding event tree is developed based on step b) and the expected response of all accident consequence mitigation systems is examined, and typical event sequences are identified. The frequency results of solid-state micro-reactor event sequences are obtained based on PSA analysis, and the solid-state micro-reactor design basis events are obtained based on risk guidance.

[0044] In one embodiment, the definition of design basis events in the International Micro Reactor Licensing Benchmark Event Classification (it is expected that it will not occur during the life of the nuclear power plant, and the frequency average is 10 -4 / Pile-year-10 -2 According to this definition, the following five solid-state microreactor design basis events are obtained: SSR:0001, LSOHP:0001, LLOHP:0001, TOP:0001, GTRAN:0005.

[0045] Step d): Screen out the systems that serve as accident consequence mitigation systems in all solid-state micro-reactor design basis events as safety-related systems.

[0046]

[0047]

[0048] Table 1 Screening table of solid-state micro-reactor safety-related systems

[0049] In one embodiment, for the five solid-state micro-reactor design basis events in step c), the screening results are shown in Table 1 (where "No" means it is not a safety-related system; "-" means it is not in the event tree of the design basis event, that is, it is not related to the development process of the design basis event), and it is determined that the solid-state micro-reactor safety-related systems include the emergency shutdown system, the residual heat removal system and the chamber system.

[0050] Step e): Figure 3 As shown, only the design basis events in which safety-related systems are successfully executed are screened out as the design basis accidents of the solid-state micro-reactor.

[0051] In one embodiment, the selected solid-state micro-reactor design basis accidents include:

[0052] SSR: 0001, after SSR occurs, JNA is successful and CS is successful;

[0053] LSOHP: 0005, after LSOHP occurs, ROD succeeds, DMS fails, JNA succeeds, and CS succeeds;

[0054] LLOHP: 0003, after LLOHP occurs, ROD succeeds, DMS fails, and CS succeeds;

[0055] TOP: 0001, after TOP occurs, ROD succeeds, JNA succeeds, and CS succeeds;

[0056] GTRAN:0005, after GTRAN occurs, ROD succeeds, DMS fails, JNA succeeds, and CS succeeds.

[0057] In other embodiments, when the structural design, operating parameters, risk guidance reference standards and the probability of underlying basic events of the solid-state micro-reactor change, the selection results of the solid-state micro-reactor design basis accidents may also change.

[0058] An embodiment of another aspect of the present invention provides a system for selecting a solid-state micro-reactor design basis accident. The system includes a memory and a processor. The memory stores a calculation program. When the calculation program is executed by the processor, the method for selecting a solid-state micro-reactor design basis accident provided in any of the aforementioned embodiments can be implemented.

[0059] Specifically, in some embodiments, the calculation program includes: an acquisition module, which is used to obtain the design information of the solid-state micro-reactor that needs to be analyzed from a database; an evaluation module, which is used to use the design information of the solid-state micro-reactor obtained by the acquisition module to carry out probabilistic safety evaluation and complete relevant quantitative calculations based on given risk guidelines; a processing module, which is used to obtain the solid-state micro-reactor design benchmark events by limiting the event sequence with a frequency range of occurrence, and further carry out safety-related system screening; a selection module, which is used to derive the solid-state micro-reactor design benchmark accidents from the design benchmark events according to the processing results of the processing module; and an output module, which has the function of packaging and outputting the selection results of the selection module as a visualization file or a data packet for docking with other safety management systems.

[0060] In different embodiments, the above-mentioned calculation program can be specially written in a computer language, or can be set and implemented in a general nuclear power plant probabilistic safety assessment software or other analysis software, wherein the acquisition of data and the transmission between modules can be completed automatically by the program, or can be realized by manual operation. The computing device can be configured as a general-purpose computer, or as a specially built dedicated computing device, or can also use a virtual machine or cloud computing equipment, etc.

[0061] The method for selecting the solid-state micro-reactor design basis accident provided in the above embodiment can combine the design characteristics of the solid-state micro-reactor, obtain the design basis event through reasonable safety assessment and screen the safety-related systems, and improve the pertinence of the selection of the design basis accident. The selection of the solid-state micro-reactor design basis accident achieved by this method has better sufficiency than the design basis accident obtained by the deterministic method, and can effectively improve the safety management level of the solid-state micro-reactor.

[0062] The purpose of the above embodiments is to further explain the present invention in detail in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, the optimization or equivalent replacement of the method steps involved, and the combination of the implementation methods in different embodiments without conflict of principle, all fall within the protection scope of the present invention.

Claims

1. A method for selecting a design basis accident for a solid-state micro-reactor, characterized in that: The following steps are involved: Step a): providing a list of solid-state micro-reactor initiating events and the occurrence frequencies of corresponding initiating events; Step b): providing a key safety function list and a PSA modeling system, establishing an event tree according to the initiating event list, obtaining an event sequence corresponding to the initiating event, and calculating the occurrence frequency of the event sequence; Step c): obtaining a solid-state micro-reactor design basis event based on the frequency of the event sequence and a given event sequence frequency limit; Step d): Screening out systems that serve as accident consequence mitigation systems in all the solid-state micro-reactor design basis events as safety-related systems; Step e): Screening out the design basis events in which only the safety-related systems are successfully executed as solid-state micro-reactor design basis accidents.

2. The method for selecting a solid-state micro-reactor design basis accident according to claim 1, characterized in that: In the step a), the initiating event is obtained through a failure mode and effects analysis method.

3. The method for selecting a solid-state microreactor design basis accident according to claim 1 or 2, characterized in that: The initiating events in step a) include accidental shutdown, general transient, transient overpower, failure of a small number of heat pipes, failure of a large number of heat pipes, accidental opening of residual exhaust valves and failure of core matrix.

4. The method for selecting a solid-state micro-reactor design basis accident according to claim 1 or 2, characterized in that: The key safety functions in the key safety function list in step b) include reactivity control, decay heat removal and radioactivity containment.

5. The method for selecting a solid-state micro-reactor design basis accident according to claim 1, characterized in that: The event tree in step b) is constructed by determining the system responses required to mitigate the consequences of each of the initiating events.

6. The method for selecting a solid-state micro-reactor design basis accident according to claim 1 or 5, characterized in that: The probabilities of success and failure of the event tree branches in step b) are calculated by means of a fault tree.

7. The method for selecting a solid-state micro-reactor design basis accident according to claim 1, characterized in that: The frequency of the solid-state micro-reactor design basis event in step c) is 10 -4 / Pile-year-10 -2 / pile years.

8. The method for selecting a solid-state micro-reactor design basis accident according to claim 1, characterized in that: The safety-related systems in step d) include an emergency shutdown system, a residual heat removal system and a chamber system.

9. A system for selecting design basis accidents of solid-state micro-reactors, comprising a memory and a processor, characterized in that: The memory stores a calculation program, and when the calculation program is executed by the processor, the method for selecting a solid-state micro-reactor design basis accident as described in any one of claims 1 to 8 can be implemented.

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