Method and device for determining severe accident environmental conditions in containment vessel

Abstract

The invention relates to a method and a device for determining severe accident environmental conditions in a containment. The method comprises the following steps: determining an accident stage based on a serious accident judgment criterion, and determining key influence factors of a serious accident environment condition by combining the accident process characteristics of the accident stage; based on the serious accident phenomena associated with the key influence factors, analyzing and determining a typical serious accident sequence in combination with a probability theory and a determination theory, and establishing a reactor analysis model based on the typical serious accident sequence; based on the reactor analysis model, in combination with a serious accident mitigation strategy, performing calculation analysis on the typical serious accident sequence to obtain a temperature and pressure calculation curve of the typical serious accident sequence; and according to a serious accident envelope curve determination principle, on the basis of the temperature and pressure calculation curve, fitting an envelope curve for representing serious accident environmental conditions in the containment. By adopting the method, the severe accident environment condition in the containment can be determined.

Description

Technical Field

[0001] This application relates to the field of nuclear power safety technology, and in particular to a method and apparatus for determining severe accident environmental conditions within a containment. Background Technology

[0002] In the event of a serious accident at a nuclear power plant, the environmental conditions within the containment vessel are crucial for assessing the consequences of the accident, developing emergency response measures, and conducting post-accident safety analyses.

[0003] In the field of nuclear safety, the traditional determination of severe accident environmental conditions mainly relies on artificially constructing a small number of extremely conservative envelope conditions to represent and cover a wide range of possible severe accident sequences. The identification of severe accident equipment also heavily depends on reactor type-specific analysis conclusions, resulting in a lack of universality and often requiring repeated identification, which undoubtedly increases the economic burden on nuclear power plants significantly. Furthermore, there is no unified method for determining the envelope curve of severe accident environmental conditions; significant differences exist domestically and internationally in the selection of analytical models, accident sequence screening criteria, and envelope construction methods, making the methods for determining severe accident environmental conditions highly uncertain.

[0004] Therefore, the lack of a method for determining the environmental conditions of severe accidents is a problem that urgently needs to be solved. Summary of the Invention

[0005] Therefore, it is necessary to provide a method and apparatus for determining the environmental conditions of a severe accident inside a containment, addressing the aforementioned technical problems.

[0006] In a first aspect, this application provides a method for determining the environmental conditions of a severe accident within a containment, comprising:

[0007] Based on the criteria for judging serious accidents, the accident stage is determined, and combined with the characteristics of the accident process at each stage, the key influencing factors of the environmental conditions of serious accidents are determined.

[0008] Based on the severe accident phenomena associated with key influencing factors, a typical severe accident sequence is determined by combining probability theory and determinism, and a reactor analysis model is established based on the typical severe accident sequence.

[0009] Based on the reactor analysis model and combined with severe accident mitigation strategies, calculations and analyses were performed on typical severe accident sequences to obtain temperature and pressure calculation curves for typical severe accident sequences.

[0010] Based on the principle of determining the envelope curve for severe accidents, an envelope curve is fitted to characterize the environmental conditions of severe accidents inside the containment, based on temperature and pressure calculation curves.

[0011] In one embodiment, determining the stage of a serious accident based on serious accident judgment criteria includes:

[0012] According to the pre-set criteria for judging serious accidents, the serious accident stage is divided into the pre-serious accident stage and the serious accident stage.

[0013] In one embodiment, based on the characteristics of the accident process at each stage, key influencing factors of the severe accident environmental conditions are determined, including:

[0014] Serious accidents include breach accidents and non-breach accidents;

[0015] Based on the characteristics of the early-stage accident process of breach-type and non-breach-type accidents, the rate of temperature and pressure rise and the duration of the pre-severe accident stage are adopted as key influencing factors of the pre-severe accident stage.

[0016] Based on the accident process characteristics after mitigation measures are implemented, peak temperatures and pressures, the thermal-hydraulic response characteristics within the containment under long-term steady-state conditions, and their duration are used as key influencing factors in the severe accident phase.

[0017] In one embodiment, a typical severe accident sequence is determined by combining probabilistic and deterministic analysis, including:

[0018] Obtain the cutoff frequency;

[0019] By combining probability theory to analyze the correlation of key influencing factors in serious accidents, a preliminary list of typical serious accident sequences is selected based on the cutoff frequency. Then, based on the list of serious accident sequences, determinism and engineering experience are combined to determine the typical serious accident sequences.

[0020] In one embodiment, a reactor analysis model is established based on a typical severe accident sequence, including:

[0021] Identifying severe accident phenomena based on typical severe accident sequences;

[0022] Multiple model nodes are defined based on reactor design and severe accident phenomena;

[0023] Based on multiple model nodes, a reactor analysis model is established using a severe accident analysis program. Key parameters of the reactor analysis model are set. The reactor analysis model has the function of simulating containment thermal components and compartments, as well as simulating local harsh environments.

[0024] In one embodiment, based on the principle for determining the severe accident envelope curve, an envelope curve characterizing the severe accident environmental conditions within the containment is fitted using temperature and pressure calculation curves, including:

[0025] In the pre-severe accident stage, based on the initial temperature and pressure rise rate and the duration of the pre-severe accident stage, the envelope curve of the calculated temperature and pressure curves of the pre-severe accident stage is fitted; the temperature and pressure rise rate is determined based on the breach-type accident where the mass energy release in the early stage meets the preset conditions; the duration of the pre-severe accident stage is determined based on the accident sequence where the accident process meets the preset conditions.

[0026] During the severe accident phase, the envelope curves of the temperature and pressure calculation curves during the severe accident phase are fitted based on the peak temperature and pressure inside the containment and their duration. The peak temperature and pressure during the severe accident phase are taken as the highest peak value at the beginning or the value at system startup.

[0027] By adjusting the envelope curves for the pre-accident and serious accident stages based on the local environmental conditions inside the containment, the envelope curves for serious accident environmental conditions are obtained.

[0028] In one embodiment, based on the pre-accident process characteristics of breach-type and non-breach-type accidents, the rate of temperature and pressure rise and the duration of the pre-severe accident stage are used as key influencing factors for the pre-severe accident stage, including:

[0029] Based on the characteristics of the early-stage mass-energy release in breach-type accidents, the rate of temperature and pressure rise is adopted as a key influencing factor in the pre-severe stage of accidents.

[0030] Based on the different durations of the pre-accident process in breach-type and non-breach-type accidents, the duration of the pre-accident stage is adopted as a key influencing factor in the pre-accident stage of a serious accident.

[0031] In one embodiment, based on the accident process characteristics after mitigation measures are implemented, peak temperatures and pressures, as well as the characteristics and duration of the containment thermo-hydraulic response under long-term steady-state conditions, are used as key influencing factors in the severe accident phase, including:

[0032] Based on the accident process characteristics of the containment thermal-hydraulic phenomena introduced after the implementation of mitigation measures, peak temperature and pressure are used as key influencing factors in the severe accident stage.

[0033] Based on the accident process characteristics that the temperature and pressure inside the containment will reach a stable state in the long term after the implementation of mitigation measures, the characteristics and duration of the thermal-hydraulic response inside the containment under the long-term stable state are used as the key influencing factors in the severe accident stage.

[0034] In one embodiment, typical severe accident sequences are determined by combining determinism and engineering experience with a severe accident sequence list, including:

[0035] Based on the list of serious accident sequences, combined with determinism and engineering experience, typical serious accident sequences that can cover different accident processes and characterize typical serious accident phenomena are selected.

[0036] Among them, the selection of breach-type conditions in typical severe accident sequences should identify different breach locations.

[0037] Secondly, this application also provides an apparatus for determining the environmental conditions of a severe accident inside a containment, comprising:

[0038] The determination module is used to determine the accident stage based on the principles of severe accident judgment, and to determine the key influencing factors of the environmental conditions of severe accidents in combination with the accident process characteristics of the accident stage.

[0039] A module is established to identify severe accident phenomena based on the correlation of key influencing factors, and to determine typical severe accident sequences by combining probability theory and determinism analysis. A reactor analysis model is then established based on these typical severe accident sequences.

[0040] The calculation module is used to perform calculations and analyses on typical severe accident sequences based on the reactor analysis model and combined with severe accident mitigation strategies, and to obtain the temperature and pressure calculation curves of typical severe accident sequences.

[0041] The fitting module is used to fit an envelope curve that characterizes the environmental conditions of a severe accident inside the containment, based on the temperature and pressure calculation curves and the principle for determining the envelope curve of a severe accident.

[0042] The aforementioned method and apparatus for determining the environmental conditions of a severe accident within the containment vessel firstly, based on the principles for judging severe accidents, determine the accident stage and, combined with the characteristics of the accident process at each stage, identify the key influencing factors of the severe accident environmental conditions. Secondly, based on the severe accident phenomena associated with the key influencing factors, and combining probability theory and determinism, determine typical severe accident sequences, and establish a reactor analysis model based on these sequences. Thirdly, based on the reactor analysis model and in conjunction with severe accident mitigation strategies, perform calculations and analyses on the typical severe accident sequences to obtain temperature and pressure calculation curves for these sequences. Finally, according to the principles for determining the severe accident envelope curve, and based on the temperature and pressure calculation curves, fit an envelope curve to characterize the environmental conditions of a severe accident within the containment vessel. Thus, by systematically proposing an analytical method for severe accident environmental conditions, the determinism of severe accident environmental condition prediction is ensured, avoiding the phenomenon of repeated qualification of nuclear power plant equipment due to insufficient universality of equipment qualification conditions determined based on severe accident environmental conditions. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a flowchart illustrating a method for determining severe accident environmental conditions within a containment in one embodiment;

[0045] Figure 2 This is a schematic diagram of the pressure during the severe accident phase following a small breach accident inside the containment in one embodiment.

[0046] Figure 3 This is a flowchart illustrating a method for determining severe accident environmental conditions within a containment in another embodiment;

[0047] Figure 4 This is a flowchart illustrating the process of identifying environmental conditions for a severe accident in one embodiment.

[0048] Figure 5 This is a schematic diagram of the node division of a containment system analysis model in one embodiment;

[0049] Figure 6 This is a schematic diagram of a large pressurized water reactor accident mitigation strategy in one embodiment;

[0050] Figure 7 This is a schematic diagram illustrating the determination of the pressure envelope curve under severe accident environmental conditions in one embodiment;

[0051] Figure 8 This is a schematic diagram illustrating the determination of the temperature envelope curve under severe accident environmental conditions in one embodiment.

[0052] Figure 9 This is a structural block diagram of an apparatus for determining severe accident environmental conditions within a containment in one embodiment. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0054] In one exemplary embodiment, such as Figure 1As shown, a method for determining the environmental conditions of a severe accident within a containment is provided. Taking a terminal as an example, the terminal can be, but is not limited to, various personal computers, laptops, smartphones, tablets, drones, low-altitude aircraft, IoT devices, and portable wearable devices. IoT devices can include smart speakers, smart TVs, smart air conditioners, smart vehicle devices, projection devices, etc. Portable wearable devices can include smartwatches, smart bracelets, head-mounted devices, etc. Head-mounted devices can be virtual reality (VR) devices, augmented reality (AR) devices, smart glasses, etc. In this embodiment, the method includes steps 102 to 108. Wherein:

[0055] Step 102: Determine the accident stage based on the criteria for determining a serious accident, and determine the key influencing factors of the environmental conditions of a serious accident by combining the characteristics of the accident process at each stage.

[0056] Specifically, the containment structure is a critical safety facility in a nuclear power plant. Its main function is to contain radioactive materials within the reactor building to the greatest extent possible during a severe accident, preventing them from leaking into the external environment and thus protecting public and environmental safety. Severe accident environmental conditions refer to the extremely harsh and dynamically changing environmental conditions experienced inside the containment structure during a severe accident at a nuclear power plant, far exceeding the environmental conditions inside the containment under normal design conditions.

[0057] The criteria for determining a severe accident are based on a preset core exit temperature threshold, which classifies the accident stages. The key influencing factors of severe accident environmental conditions are essentially the key influencing factors affecting equipment qualification within those conditions. When determining severe environmental accident conditions, identifying the key influencing factors requires considering both the accident stage's progression characteristics and equipment qualification practices to determine the key influencing factors affecting equipment qualification within the severe accident environmental conditions.

[0058] Step 104: Based on the severe accident phenomena associated with key influencing factors, combine probability theory and determinism to determine typical severe accident sequences, and establish a reactor analysis model based on the typical severe accident sequences.

[0059] The reactor system analysis model is a computational model based on severe accident procedures, capable of simulating the thermal-hydraulic, chemical, and radioactive behavior of the reactor system under accident conditions. The determination of typical severe accident sequences requires a combination of probabilistic and deterministic analysis. Initial screening is conducted based on probabilistic analysis, using the results of a Level 1 Probabilistic Safety Analysis (PSA) of the nuclear power plant, and following a preset cutoff frequency to identify initial event sequences that could lead to severe accidents, forming a preliminary list of accident sequences. Building upon the Level 1 PSA screening, and combining deterministic analysis and engineering experience, typical severe accident sequences are further selected.

[0060] Specifically, each key influencing factor has a corresponding specific physical phenomenon. By analyzing the impact of these phenomena on severe environmental conditions inside the containment, we can determine which typical severe accident sequences will trigger severe accident phenomena associated with key influencing factors, providing a basis for subsequent sequence screening.

[0061] Step 106: Based on the reactor analysis model and combined with the severe accident mitigation strategy, perform calculation and analysis on typical severe accident sequences to obtain the temperature and pressure calculation curves of typical severe accident sequences.

[0062] The temperature and pressure calculation curves for a typical severe accident sequence are obtained through numerical simulation, describing the temperature and pressure changes over time at a point or region within the containment during the accident process. Severe accident mitigation strategies are system actions and operator procedures designed to control or mitigate the consequences of severe accidents.

[0063] For example, for a given severe accident sequence, if there are two mitigation paths for containment heat dissipation according to the severe accident mitigation strategy, a deterministic analysis of the accident process and phenomena is performed, and a severe accident analysis program is used for simulation calculation. Different mitigation paths should determine different temperature and pressure calculation curves within the containment.

[0064] Step 108: Based on the principle of determining the envelope curve for severe accidents, and using temperature and pressure calculation curves, fit an envelope curve to characterize the environmental conditions of severe accidents inside the containment.

[0065] Among them, the envelope curve used to characterize the severe accident environment conditions inside the containment is an artificially fitted, conservative curve. It lies above the calculated curves of all possible real physical processes and can enclose all uncertainties, thereby ensuring that the equipment qualification based on this curve is safe under any expected accident scenario.

[0066] For example, multiple temperature and pressure calculation curves based on typical severe accident sequences are synthesized into one or a set of conservative and representative envelope curves for equipment qualification, according to a set of scientific principles for determining the severe accident envelope. The principles for determining the severe accident envelope are a set of criteria based on the physical process and engineering conservatism of severe accidents, ensuring that the final fitted curve conservatively covers the environmental conditions within the containment under all typical severe accident sequences, while also being both engineering reasonable and economical.

[0067] The aforementioned method for determining the environmental conditions of a severe accident within the containment facility involves the following steps: First, based on the severe accident determination criteria, the stage of a severe accident is identified. Combining this with the accident process characteristics of each stage, key influencing factors of the environmental conditions are determined. Second, based on the severe accident phenomena associated with these key influencing factors, a typical severe accident sequence is determined using probability theory and determinism. A reactor analysis model is then established based on this sequence. Third, based on the reactor analysis model and combined with severe accident mitigation strategies, calculations and analyses are performed on the typical severe accident sequence to obtain temperature and pressure calculation curves. Finally, according to the principles for determining the severe accident envelope curve, an envelope curve characterizing the environmental conditions of a severe accident within the containment facility is fitted based on the temperature and pressure calculation curves. Therefore, by systematically proposing an analytical method for severe accident environmental conditions, the determinism of severe accident environmental condition prediction is ensured, avoiding the need for repeated qualification of nuclear power plant equipment in the event of a severe accident due to insufficient universality of equipment qualification conditions determined based on severe accident environmental conditions.

[0068] In one embodiment, determining the stage of a serious accident based on a serious accident judgment criterion includes: dividing the serious accident stage into a pre-serious accident stage and a serious accident stage according to a preset serious accident judgment criterion.

[0069] The criteria for determining a severe accident are based on a preset core outlet temperature threshold of 650°C. This threshold is used to classify the accident stages. The pre-severe accident stage is defined as the period from the onset of the accident until the core outlet temperature reaches 650°C. The severe accident stage extends from when the core outlet temperature reaches 650°C to the long-term post-severe accident phase.

[0070] Alternatively, the pre-serious accident stage can also be called the Pre-SA stage, and the serious accident stage can also be called the SA stage.

[0071] In this embodiment, by dividing the severe accident stage into the pre-severe accident stage and the severe accident stage according to the preset core outlet temperature threshold, the severe accident environmental conditions can be divided into two parts according to the accident process, which is more conducive to the subsequent further analysis of the severe accident environmental conditions.

[0072] In a specific embodiment, based on the accident process characteristics at each stage of the accident, key influencing factors of the environmental conditions of a severe accident are determined, including: severe accidents include breach-type accidents and non-breach-type accidents; based on the early accident process characteristics of breach-type and non-breach-type accidents, the rate of temperature and pressure rise and the duration of the pre-severe accident stage are used as key influencing factors of the pre-severe accident stage; based on the accident process characteristics after the implementation of mitigation measures, the peak temperature and pressure, the thermal-hydraulic response characteristics of the containment under long-term steady state, and their duration are used as key influencing factors of the severe accident stage.

[0073] Specifically, the rate of temperature and pressure rise directly determines the temperature rise time and peak temperature and pressure during the thermal shock of equipment qualification. Since reactor condition deterioration progresses from the initial stage of an accident to a severe accident, the availability of equipment and instruments required under severe accident conditions must be ensured by considering the duration of the pre-severe accident phase during equipment qualification. This pre-severe accident phase is also the duration of the environmental conditions preceding a severe accident.

[0074] For example, when a reactor enters a severe accident phase, operators typically implement mitigation measures according to severe accident management guidelines to mitigate the accident. Severe accident mitigation measures include opening the severe accident relief valve to depressurize the primary circuit for a high-pressure accident sequence, or activating the In-Vessel Retention System (IVR) to inject water into the reactor sump. Other severe accident mitigation measures exist and must be considered based on the specific circumstances. The core objective of the IVR is to retain molten core material inside the reactor pressure vessel in the event of a severe nuclear reactor core meltdown accident, thereby preventing more catastrophic consequences.

[0075] Due to the implementation of severe accident mitigation measures, reactor heat is continuously released into the containment via the IVR (Indoor Respirator). The containment heat removal system operates to control the temperature and pressure within the containment, eventually leading to a long-term stable state. During equipment qualification, the thermal-hydraulic response characteristics and their duration within the containment under long-term stable conditions are assessed. The duration directly impacts the cumulative heat load on equipment and instrumentation. Therefore, the thermal-hydraulic response characteristics and their duration within the containment under long-term stable conditions are considered key influencing factors during the severe accident phase.

[0076] In this embodiment, the critical factors influencing equipment qualification at each stage are determined by dividing the severe accident environmental conditions of a nuclear power plant into stages and based on the calculation results. These critical factors have universal applicability, are not limited by reactor type design, and help to standardize the process of determining severe accident environmental conditions.

[0077] In one specific embodiment, the determination of typical severe accident sequences by combining probability theory and deterministic analysis includes: obtaining the cutoff frequency; analyzing the severe accident phenomena associated with key influencing factors using probability theory to obtain the probability theory analysis results; screening a preliminary list of typical severe accident sequences according to the cutoff frequency; and then determining the typical severe accident sequences based on the list of severe accident sequences by combining deterministic analysis and engineering experience.

[0078] The cutoff frequency is set based on common practices in probabilistic safety analysis in the nuclear safety field. The purpose of using the cutoff frequency is to screen out typical severe accident sequences that significantly contribute to the core damage frequency, ensuring that the preliminary list covers all important accident scenarios while also being engineering-manageable. Optionally, the cutoff frequency is a CDF value greater than... / Pile of years.

[0079] In this embodiment, based on the key influencing factors and probabilistic analysis results, the typical and envelope accident sequences of each key factor are determined by reverse deduction. The selection method of analyzing from factors to phenomena and then from phenomena to typical severe accident sequences makes the selected accident sequences more targeted and the curve determination closer to reality, which helps to reduce the cost of equipment appraisal.

[0080] In one embodiment, a reactor analysis model is established based on a typical severe accident sequence, including: determining severe accident phenomena based on the typical severe accident sequence; dividing multiple model nodes based on reactor design and severe accident phenomena; establishing a reactor analysis model using a severe accident analysis program based on the multiple model nodes; setting key parameters of the reactor analysis model; the reactor analysis model has the function of simulating containment thermal components and compartments, and also has the function of simulating local harsh environments.

[0081] The key parameters for setting the reactor analysis model include the initial state parameters and boundary conditions. Based on a selected typical severe accident sequence, the initial state of the accident sequence, the system failure state, and the severe accident mitigation strategy set according to the time series are also defined. Optionally, the initial state parameters include initial temperature, pressure, and humidity. The initial state of the accident sequence includes the location and size of the breach.

[0082] Specifically, dividing the system into multiple model nodes is based on the reactor design and the distribution characteristics of severe accident phenomena, allowing for a refined modeling of the overall containment space. A model node is a discretized unit of the continuous physical space of the containment in the severe accident analysis program. Each node represents a relatively uniform control volume in terms of thermal-hydraulic parameters, used to solve the mass, momentum, and energy equations.

[0083] In this embodiment, by refining the construction of the reactor system analysis model, the complex and variable thermal-hydraulic phenomena within the containment can be simulated more accurately, providing a solid foundation for subsequent calculations and analyses. Simultaneously, by rationally setting the model's key parameters, it can be ensured that the model can realistically reflect various conditions during the accident process, improving the reliability and effectiveness of the simulation results. Furthermore, it contributes to a deeper understanding of the physical processes within the containment under severe accident conditions, providing strong support for equipment qualification and the safety design of nuclear power plants.

[0084] In one embodiment, based on the principle for determining the envelope curve of a severe accident, an envelope curve characterizing the environmental conditions of a severe accident within the containment is fitted using temperature and pressure calculation curves. This includes: in the pre-severe accident stage, fitting the envelope curves of the calculated temperature and pressure curves for the pre-severe accident stage based on the initial rate of temperature and pressure rise and the duration of the pre-severe accident stage; the rate of temperature and pressure rise is determined based on a breach-type accident where the initial mass-energy release meets preset conditions; the duration of the pre-severe accident stage is determined based on an accident sequence where the accident process meets preset conditions; in the severe accident stage, fitting the envelope curves of the calculated temperature and pressure curves for the severe accident stage based on the peak values ​​of high temperature and high pressure within the containment and the duration of the thermal-hydraulic response under long-term steady-state conditions; the peak values ​​of high temperature and high pressure in the severe accident stage are taken as the initial highest peak value or the value at system startup; and adjusting the envelope curves for the pre-severe accident stage and the severe accident stage in conjunction with the local environmental conditions within the containment to obtain the envelope curve of the severe accident environmental conditions.

[0085] Among them, the breach-type accidents that meet the preset conditions in the early stage of mass and energy release are breach-type accidents with large and rapid early stage mass and energy release, such as using the analysis results of reactor cooling system large breach loss-of-coolant accident (LBLOCA) and main steam pipe breach (MSLB) as envelope conditions; the accident sequence that meets the preset conditions in the accident process is an accident sequence with slow accident process, that is, a plant blackout (SBO) type of condition, because this type of accident has a long duration of the pre-severe accident stage.

[0086] Specifically, the peak temperature and pressure during a severe accident phase are determined by using the initial highest peak value or the value at system startup as the peak pressure, based on the influence of heated systems within the containment. If heated systems exist within the containment, the temperature and pressure inside the containment will be lower than the peak temperature and pressure caused by the initial mass-energy release during the accident after operation. From an envelope perspective, the initial peak temperature and pressure can still be considered as a reference during the medium to long term. If there are no effective heating methods within the containment, containment filtration and venting measures are used. Since the function of containment filtration and venting measures is to address the residual risk of containment overpressure, the peak containment pressure during a severe accident phase is determined by using the value at system startup.

[0087] Optionally, if there are more severe local environmental conditions than the envelope curve, the pressure or temperature peak should be considered for the envelope curve, and the duration should be determined based on the specific influencing factors.

[0088] In this embodiment, by establishing principles for determining the envelope curve of a severe accident, the principles for determining the envelope curve of a severe accident are implemented and can be generalized, thus realizing the determination of the envelope curve of a severe accident. The principles for determining the envelope curve of a severe accident fully consider the mass-energy release characteristics of different types of accidents and the impact of heated systems or filtration and emission measures within the containment on environmental conditions. They are adaptive principles proposed for determining the environmental conditions of severe accidents.

[0089] In one embodiment, based on the pre-accident process characteristics of breach-type accidents and non-breach-type accidents, the heating and pressurization rate and the duration of the pre-severe accident stage are used as key influencing factors of the pre-severe accident stage, including: based on the pre-accident process characteristics of mass-energy release in the early stage of breach-type accidents, the heating and pressurization rate is used as a key influencing factor of the pre-severe accident stage; based on the pre-accident process characteristics of different durations of the early accident process between breach-type accidents and non-breach-type accidents, the duration of the pre-severe accident stage is used as a key influencing factor of the pre-severe accident stage.

[0090] Specifically, based on the characteristics of the pre-accident process of mass-energy release in the early stages of breach-type accidents, the rate of temperature and pressure rise is adopted as a key influencing factor in the pre-severe accident phase. This is because mass-energy release occurs in the early stages of breach-type accidents, leading to a rapid increase in pressure and temperature within the containment. The magnitude of the mass-energy release affects the rate of temperature and pressure rise of the containment in the pre-severe accident phase. The rate of temperature and pressure rise directly determines the temperature rise time and peak temperature and pressure of the equipment during the thermal shock assessment.

[0091] For example, in breach accidents, due to coolant loss, the accident progresses rapidly, and the reactor quickly transitions from the pre-accident stage to the severe accident stage. In non-breach accidents, due to the high-pressure sequence, there is no coolant loss, but the core temperature continuously rises and deteriorates due to the lack of heat conduction, until the core outlet temperature reaches 650°C, and the accident progresses slowly. Therefore, based on the different durations of the pre-accident stages in breach and non-breach accidents, the duration of the severe accident pre-stage is used as a key influencing factor. The evaluation results are determined based on the durations of the severe accident pre-stage for several typical accident scenarios, as shown in the table below.

[0092] Table 1

[0093]

[0094] In this embodiment, by distinguishing between the rapid mass-energy release characteristics of breach-type accidents and the slow process characteristics of non-breach-type accidents, it is possible to accurately identify and extract the heating and pressurization rates that pose the greatest challenge to the thermal shock of the equipment, as well as the duration before a severe accident that poses the greatest challenge to the long-term endurance of the equipment.

[0095] In one embodiment, based on the accident process characteristics after the implementation of mitigation measures, the peak values ​​of temperature and pressure, the characteristics of the thermal-hydraulic response within the containment under long-term steady-state conditions, and their duration are used as key influencing factors for the severe accident stage. This includes: based on the accident process characteristics of the thermal-hydraulic phenomena introduced into the containment after the implementation of mitigation measures, using the peak values ​​of temperature and pressure as key influencing factors for the severe accident stage; and based on the accident process characteristics of the containment temperature and pressure reaching a long-term steady state after the implementation of mitigation measures, using the duration of the thermal-hydraulic response within the containment under long-term steady-state conditions as key influencing factors for the severe accident stage.

[0096] Specifically, based on the accident process characteristics of the containment thermal-hydraulic phenomena introduced after the implementation of mitigation measures, it is also necessary to pay attention to the local temperature rise caused by severe accident phenomena, such as the temperature rise inside the containment caused by hydrogen combustion and the chemical heat released by the passive hydrogen recombiner.

[0097] For example, such as Figure 2 As shown, 12 hours after a severe accident, the two containment heat removal systems (EHR) are activated to reheat the containment. When the primary circuit pressure relief valve (SADV) is opened, a large amount of primary circuit coolant will be released into the containment through the SADV in a short period of time, causing the containment to heat up and pressurize. Figure 4When the SADV (Standard Advent Ventilation Valve) is activated, the containment pressure reaches its first peak. At the second peak, the IVR (Intake Valve Refrigerant) system is activated. After IVR activation, reactor heat is conducted through the reactor pressure vessel wall to the crater, heating the crater coolant until it boils and continuously releasing large amounts of water vapor into the containment. This causes a slow increase in temperature and pressure within the containment. At the third peak, the molten core material has migrated, leading to thermal-hydraulic phenomena and a rapid pressure increase. The next peak triggers the EHR (Emergency Heat Relief System). The EHR is an emergency heat relief system designed to dissipate heat from the containment.

[0098] For example, due to the implementation of severe accident mitigation measures, reactor heat will be continuously released into the containment via the IVR system. The containment heat removal system will be operational to effectively control the temperature and pressure within the containment, ultimately achieving a long-term stable state. Therefore, when conducting severe accident environmental condition analysis, special attention must be paid to the thermohydraulic response within the containment under long-term stable conditions. Figure 2 As shown, when two EHRs are activated to remove heat from the containment, the containment pressure remains at around 0.15 MPa for an extended period as the system's heat load and decay heat tend to balance.

[0099] Optionally, the duration is determined by the definition of the accident management status and engineering experience, and there are currently no regulatory standards for reference.

[0100] In this embodiment, by analyzing the response of thermal-hydraulic phenomena inside the containment after the implementation of severe accident mitigation measures, it is possible to identify the peak temperature and pressure and their duration during the severe accident phase as key influencing factors for the required severe accident phase. This provides a direct basis for developing a scientific and reasonable envelope curve for the severe accident environmental conditions of equipment identification that is not overly conservative.

[0101] In one embodiment, a typical severe accident sequence is determined by combining determinism and engineering experience with a severe accident sequence list. This includes: selecting typical severe accident sequences that can cover different accident processes and characterize typical severe accident phenomena based on the severe accident sequence list, combined with determinism and engineering experience; wherein, the selection of breach-type conditions in the typical severe accident sequence should determine different breach locations.

[0102] Among these, the selection criteria cover different accident processes, including fast, medium, and slow accident processes. The selection of breach-type conditions in typical severe accident sequences should identify different breach locations, because small reactors do not have a classification of large, medium, and small breaches.

[0103] For example, based on the accident phenomena associated with key influencing factors, a typical sequence of serious accidents can be determined as shown in the table below.

[0104] Table 2

[0105]

[0106] In this embodiment, the principles for determining typical severe accident sequences described above can systematically and comprehensively screen out typical severe accident sequences, avoiding subjective arbitrariness, improving the accuracy and reliability of environmental condition analysis, and providing scientific and unified input conditions for subsequent equipment qualification, thereby reducing qualification costs and improving the safety and economy of nuclear power plants.

[0107] The following is for reference. Figure 3 The method for determining the environmental conditions of a severe accident inside the containment will be further illustrated by a specific embodiment.

[0108] In this embodiment, based on the core exit temperature threshold of 650°C, the accident process is divided into a pre-severe accident stage and a severe accident stage. Key influencing factors requiring attention are determined according to the accident stage. Figure 4 It is known that in the pre-severe accident stage, due to the mass-energy release phenomenon in the early stage of breach-type accidents, the rate of temperature and pressure rise is of concern. Since the time for non-breach-type accidents and breach-type accidents to enter the severe accident stage is different, the duration of the pre-severe accident stage needs to be considered. In the severe accident stage, due to the introduction of mitigation measures, thermal-hydraulic phenomena will be introduced after the implementation of mitigation measures, such as instantaneous release of mass-energy, slow release of mass-energy, or hydrogen combustion, which will lead to an increase in temperature and pressure. Therefore, the peak temperature and pressure need to be monitored. At the same time, after the implementation of measures, there will be a long-term stable state. It is necessary to monitor the thermal-hydraulic response characteristics and duration of the containment under the long-term stable state. This duration is determined by the accident management status and engineering experience.

[0109] Based on these key influencing factors, and combining probability theory, determinism, and engineering experience, a typical severe accident sequence was finally determined for calculating the environmental conditions of severe accidents.

[0110] Based on typical severe accident sequences and nuclear power plant reactor design, and combined with the above-mentioned severe accident analysis procedures, a reactor system analysis model is established, key parameters are set, and nodes are divided according to different phenomena within the containment. The node division is as follows: Figure 5 As shown. Combined with Figure 6The severe accident mitigation strategy shown presents two mitigation paths for containment heat dissipation. Different mitigation paths require different temperature and pressure calculation curves within the containment. During equipment availability and qualification processes, functional classification of the equipment must be considered. This severe accident mitigation strategy consists of two paths: for non-SBO type accidents, EIS injection is performed 20 minutes after the severe accident, followed by no action for 72 hours; for SBO type accidents, IVR is activated within 1 hour of the severe accident, PIVR is switched to AIVR 12 hours after the severe accident, and the containment heating system is activated 24 hours after the accident.

[0111] Based on the reactor system analysis model, the pressure and temperature calculation curves for a typical severe accident sequence were obtained using a severe accident analysis program, such as... Figure 7 , Figure 8 As shown in the figure, five different temperature and pressure calculation curves were obtained.

[0112] Based on the envelope curve principle, determine the envelope curve for a severe accident. The envelope curves for pressure and temperature in a severe accident are as follows: Figure 7 , Figure 8 As shown. According to Figure 7First, focus on the pre-severe accident phase. 30 seconds represents the time required for rapid pressure increase, 27 hours represents the duration of the pre-severe accident phase, and the curve duration after 27 hours represents the duration of the severe accident phase. The envelope curve within 30 seconds abruptly increases from 0 MPa to 0.52 MPa with a steep slope, determined based on calculations of LBLOCA-type rupture accidents with large and rapid initial mass-energy release. These accidents cause a rapid pressure increase in a very short time. By calculating the temperature and pressure rise rates of such accidents, the temperature rise time of 30 seconds and the pressure peak of 0.52 MPa in the pre-severe accident phase can be determined. The duration before 27 hours represents the upper limit of the pre-severe accident phase duration. The envelope curve for the pre-severe accident phase will encompass all sequences, especially the long pre-severe accident phase duration corresponding to slow-progressing accident sequences like SBO. Second, focus on the severe accident phase. At 27 hours, the accident officially transitions from the pre-severe accident phase to the severe accident phase. At this point, the nuclear power plant activates the containment thermal mitigation system, slowly releasing pressure within the containment. This causes the pressure to gradually decrease from 0.52 MPa until it stabilizes at 0.42 MPa after 33 hours. 0.42 MPa is the pressure envelope value after the initial mitigation measures have stabilized during the severe accident phase; this value is determined based on the envelope curve principle. Currently, there are no regulatory standards for the duration of the curve after 33 hours; it can be determined through the definition of severe accident management status and engineering experience. For example, in CPR1000 power plants, 7 days is considered as the duration of severe accident environmental conditions, providing sufficient time for the deployment and connection of off-site emergency equipment. Finally, if there are more severe local environmental conditions than those on the envelope curve, the pressure or temperature peaks must be considered in addition to the envelope curve, and the duration depends on the specific influencing factors. Figure 8 The envelope curve for determining temperature and Figure 7 The same method is used to determine the envelope curve of the pressure.

[0113] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages in other steps. It is understood that the steps in different embodiments can be freely combined as needed, and all non-contradictory solutions formed by such combinations are within the scope of protection of this application.

[0114] Based on the same inventive concept, this application also provides an apparatus for determining severe accident environmental conditions inside a containment, which is used to implement the method for determining severe accident environmental conditions inside a containment as described above. The solution provided by this apparatus is similar to the solution described in the above method. Therefore, the specific limitations of one or more apparatus embodiments for determining severe accident environmental conditions inside a containment provided below can be found in the limitations of the method for determining severe accident environmental conditions inside a containment described above, and will not be repeated here.

[0115] In one exemplary embodiment, such as Figure 9 As shown, an apparatus 900 for determining severe accident environmental conditions within a containment is provided, comprising: a determination module 902, a setup module 904, a calculation module 906, and a fitting module 908, wherein:

[0116] The determination module 902 is used to determine the accident stage based on the criteria for determining serious accidents, and to determine the key influencing factors of the environmental conditions of serious accidents in combination with the accident process characteristics of the accident stage.

[0117] Module 904 is established to identify severe accident phenomena based on the correlation of key influencing factors, and to determine typical severe accident sequences by combining probability theory and determinism. Based on these typical severe accident sequences, a reactor analysis model is established.

[0118] The calculation module 906 is used to perform calculations and analyses on typical severe accident sequences based on the reactor analysis model and combined with severe accident mitigation strategies, and to obtain the temperature and pressure calculation curves of typical severe accident sequences.

[0119] The fitting module 908 is used to fit an envelope curve that characterizes the environmental conditions of a severe accident inside the containment, based on the temperature and pressure calculation curves and the principle for determining the envelope curve of a severe accident.

[0120] In one embodiment, the determining module is further configured to divide the serious accident stage into a pre-serious accident stage and a serious accident stage according to a preset serious accident judgment criterion.

[0121] In one embodiment, the determination module is further configured to include severe accidents as breach-type accidents and non-breach-type accidents; based on the early accident process characteristics of breach-type accidents and non-breach-type accidents, the rate of temperature and pressure rise and the duration of the pre-severe accident stage are used as key influencing factors of the pre-severe accident stage; based on the accident process characteristics after the implementation of mitigation measures, the peak temperature and pressure, the thermal-hydraulic response characteristics of the containment under long-term steady state and their duration are used as key influencing factors of the severe accident stage.

[0122] In one embodiment, the module is also used to obtain the cutoff frequency; analyze the serious accident phenomena associated with key influencing factors in combination with probability theory to obtain the probability theory analysis results; screen a preliminary list of typical serious accident sequences according to the cutoff frequency; and then determine the typical serious accident sequences based on the list of serious accident sequences in combination with determinism and engineering experience.

[0123] In one embodiment, the module is further configured to determine severe accident phenomena based on typical severe accident sequences; divide multiple model nodes based on reactor design and severe accident phenomena; establish a reactor analysis model using a severe accident analysis program based on the multiple model nodes; set key parameters of the reactor analysis model; and the reactor analysis model has the function of simulating containment thermal components and compartments, as well as the function of simulating local harsh environments.

[0124] In one embodiment, the fitting module is further configured to, in the pre-severe accident phase, fit an envelope curve of the calculated temperature and pressure curves for the pre-severe accident phase based on the initial rate of temperature and pressure rise and the duration of the pre-severe accident phase; the rate of temperature and pressure rise is determined based on a breach-type accident where the initial mass-energy release meets preset conditions; the duration of the pre-severe accident phase is determined based on an accident sequence where the accident process meets preset conditions; in the severe accident phase, based on the peak temperature and pressure values ​​and duration within the containment, fit an envelope curve of the calculated temperature and pressure curves for the severe accident phase; the peak temperature and pressure values ​​in the severe accident phase are taken as the initial highest peak value or the value at system startup; and the envelope curves for the pre-severe accident phase and the severe accident phase are adjusted in conjunction with the local environmental conditions within the containment to obtain the envelope curve of the severe accident environmental conditions.

[0125] In one embodiment, the determining module is further configured to use the heating and pressurization rate as a key influencing factor in the pre-severe accident stage based on the pre-accident process characteristics of mass and energy release in the early stage of breach-type accidents; and to use the duration of the pre-severe accident stage as a key influencing factor in the pre-severe accident stage based on the different pre-accident process durations of breach-type and non-breach-type accidents.

[0126] In one embodiment, the determining module is further configured to use temperature and pressure peak values ​​as key influencing factors in the severe accident stage based on the accident process characteristics of the thermal-hydraulic phenomena introduced after the implementation of mitigation measures; and to use the characteristics and duration of the thermal-hydraulic response in the containment under long-term stable conditions as key influencing factors in the severe accident stage based on the accident process characteristics of the temperature and pressure inside the containment reaching a stable state after the implementation of mitigation measures.

[0127] In one embodiment, the module is further configured to select typical severe accident sequences based on a list of severe accident sequences, combined with determinism and engineering experience, that can cover different accident processes and characterize typical severe accident phenomena; wherein, the selection of breach-type conditions in typical severe accident sequences should determine different breach locations.

[0128] The modules in the aforementioned apparatus for determining severe accident environmental conditions within a containment can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device, or stored in the memory of a computer device as software, so that the processor can invoke and execute the operations corresponding to each module.

[0129] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, artificial intelligence (AI) processors, etc., and are not limited to these.

[0130] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0131] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method of determining severe accident environmental conditions inside a containment, characterized in that, The method comprises: determining an accident phase based on a severe accident determination criterion, determining key influencing factors of a severe accident environment condition in combination with accident process characteristics of the accident phase; determining a typical severe accident sequence based on severe accident phenomena associated with the key influencing factors in combination with probabilistic and deterministic analysis, and establishing a reactor analysis model based on the typical severe accident sequence; carrying out calculation and analysis on the typical severe accident sequence based on the reactor analysis model in combination with a severe accident mitigation strategy, and obtaining temperature and pressure calculation curves of the typical severe accident sequence; fitting out an envelope curve for representing the severe accident environment condition in the containment based on the temperature and pressure calculation curves according to a severe accident envelope curve determination principle.

2. The method of claim 1, wherein, The determination of the accident phase based on the severe accident determination criterion comprises: dividing the accident phase into a pre-severe accident phase and a severe accident phase according to the severe accident determination criterion.

3. The method of claim 2, wherein, The determination of the key influencing factors of the severe accident environment condition based on the accident process characteristics of the severe accident phase comprises: the severe accident includes a break-type accident and a non-break-type accident; adopting a temperature and pressure rising rate and a pre-severe accident phase duration as the key influencing factors of the pre-severe accident phase based on the pre-accident process characteristics of the break-type accident and the non-break-type accident; adopting a temperature and pressure peak value, a containment thermal-hydraulic response characteristic and its duration in a long-term stable state as the key influencing factors of the severe accident phase based on the accident process characteristics after the implementation of a mitigation measure.

4. The method of claim 1, wherein, The determination of the typical severe accident sequence in combination with the probabilistic and deterministic analysis comprises: obtaining a truncation frequency; carrying out analysis on the severe accident phenomena associated with the key influencing factors based on the probabilistic theory to obtain a probabilistic analysis result, screening a preliminary typical severe accident sequence list according to the truncation frequency, and determining the typical severe accident sequence based on the severe accident sequence list in combination with the deterministic theory and engineering experience judgment.

5. The method of claim 1, wherein, The establishment of the reactor analysis model based on the typical severe accident sequence comprises: determining severe accident phenomena based on the typical severe accident sequence; dividing a plurality of model nodes based on the reactor design and the severe accident phenomena; establishing the reactor analysis model based on the plurality of model nodes by using a severe accident analysis program, setting key parameters of the reactor analysis model, and the reactor analysis model has the functions of simulating containment thermal components and compartments and simulating a local severe environment.

6. The method of claim 1, wherein, The fitting out of the envelope curve for representing the severe accident environment condition in the containment based on the temperature and pressure calculation curves according to the severe accident envelope curve determination principle comprises: in the pre-severe accident phase, fitting out an envelope curve of the temperature and pressure calculation curves of the pre-severe accident phase based on a temperature and pressure rising rate at the early stage of the accident and a duration of the pre-severe accident phase; the temperature and pressure rising rate is determined based on a break-type accident with a pre-set condition of early energy release; and the duration of the pre-severe accident phase is determined based on an accident sequence with a pre-set condition of accident process. Fitting an envelope curve of the temperature and pressure calculation curve of the severe accident phase based on a high temperature and high pressure peak value in the containment and a thermal-hydraulic response duration in the containment in a long-term stable state of the severe accident phase, wherein the high temperature and high pressure peak value in the severe accident phase adopts an initial highest peak value or a value at system startup as a peak pressure and temperature; Adjusting the envelope curve of the pre-severe accident phase and the severe accident phase to obtain a severe accident environmental condition envelope curve in combination with a local environmental condition in the containment.

7. The method of claim 3, wherein, The key influencing factors of the pre-severe accident phase include a temperature and pressure rise rate and a pre-severe accident phase duration based on the pre-accident process characteristics of the break-type accident and the non-break-type accident, including: The temperature and pressure rise rate is adopted as the key influencing factor of the pre-severe accident phase based on the pre-accident process characteristics of the pre-accident energy and mass ejection of the break-type accident. The pre-severe accident phase duration is adopted as the key influencing factor of the pre-severe accident phase based on the pre-accident process characteristics of different pre-accident process durations of the break-type accident and the non-break-type accident.

8. The method of claim 3, wherein, The key influencing factors of the severe accident phase include a temperature and pressure peak value, a thermal-hydraulic response characteristic in the containment in a long-term stable state and a duration thereof based on the accident process characteristics after implementation of a mitigation measure, including: The temperature and pressure peak value is adopted as the key influencing factor of the severe accident phase based on the accident process characteristics of a thermal-hydraulic phenomenon introduced into the containment after implementation of the mitigation measure. The thermal-hydraulic response characteristic in the containment in a long-term stable state and the duration thereof are adopted as the key influencing factor of the severe accident phase based on the accident process characteristics of the temperature and pressure in the containment reaching a stable state in a long term after implementation of the mitigation measure.

9. The method of claim 4, wherein, The typical severe accident sequence is determined based on the severe accident sequence list in combination with determinism and engineering experience, including: The typical severe accident sequence is screened out based on the severe accident sequence list in combination with determinism and engineering experience, which can cover different accident processes and represent typical severe accident phenomena. The screening of the break-type working condition in the typical severe accident sequence should determine different break positions.

10. An apparatus for determining severe accident environmental conditions inside a containment, characterized in that, The device includes: A determination module configured to determine an accident phase based on a severe accident judgment criterion, and determine key influencing factors of a severe accident environmental condition in combination with an accident process characteristic of the accident phase; An establishment module configured to determine a typical severe accident sequence based on a severe accident phenomenon associated with the key influencing factors in combination with probabilistic and deterministic analysis, and establish a reactor analysis model based on the typical severe accident sequence; A calculation module configured to perform calculation and analysis on the typical severe accident sequence based on the reactor analysis model in combination with a severe accident mitigation strategy, and obtain a temperature and pressure calculation curve of the typical severe accident sequence. a fitting module for fitting, on the basis of the temperature and pressure calculation curves, an envelope curve for characterizing the severe accident environmental conditions inside the containment, according to the severe accident envelope curve determination principle.

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