A steam explosion consequence analysis method and calculation device based on sampling

Abstract

A sampling-based steam explosion consequence analysis method includes the following steps: providing key influencing factors of steam explosion and their corresponding input probability distributions, and providing a steam explosion analysis program; automatically sampling the key influencing factors and generating input cards; inputting the input cards into the steam explosion analysis program to obtain a probability distribution of steam explosion consequences. This method can cover the range of variation of key factors through large-scale sampling and accurately simulate steam explosion consequences using probabilistic methods, thereby providing data support for nuclear power plant safety design and accident consequence assessment. The present invention also provides a computing device.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear power, and in particular relates to a steam explosion consequence analysis method and a calculation device based on sampling technology. Background Art

[0002] In the event of a severe nuclear reactor accident, after a core meltdown, reflooding or core melt falling into the lower chamber containing residual coolant can trigger fuel-coolant interaction (FCI) within the pressure vessel. This can lead to intense heat transfer between the two, rapid coolant evaporation, and the formation of a massive pressure wave within a very short time, known as an intra-core steam explosion. If the lower pressure vessel head fails, core melt falling into the reactor cavity can come into contact with water within the cavity, triggering fuel-coolant interaction outside the pressure vessel, known as an extra-core steam explosion. Existing steam explosion analysis primarily employs deterministic methods to analyze pressure peaks and pressure pulses using a series of conservative assumptions about initial conditions, thereby providing a worst-case scenario. However, this overly conservative analysis fails to represent actual accident conditions and is not conducive to fully analyzing and simulating diverse real-world nuclear power plant operating conditions. Therefore, providing a probabilistic steam explosion consequence analysis method that is more realistic and aligns closely with engineering practice is highly valuable for improving the accuracy of nuclear power plant safety analysis. Summary of the Invention

[0003] The purpose of the present invention is to provide a steam explosion consequence analysis method based on sampling to improve the accuracy of nuclear power plant accident consequence analysis.

[0004] According to an embodiment of the present invention, a sampling-based steam explosion consequence analysis method is provided, which includes the following steps: providing initial physical conditions of the steam explosion and a corresponding input probability distribution; automatically sampling the initial physical conditions based on the input probability distribution and generating an input card, wherein the automatic sampling process includes the following steps: providing the number of variables involved in the sampling analysis, the number of sampling times, the variable probability distribution type and the corresponding distribution parameters, sampling and outputting the sampling results; using the data of the input card to perform a simulation analysis of the steam explosion process, calculating the probability distribution of the steam explosion consequences, and analyzing the consequences of the steam explosion from a probability perspective.

[0005] Through the above method, a large number of samples can be used to cover the variation range of key influencing factors, and a more comprehensive analysis result can be obtained; by introducing the method of probability theory, the probability distribution of the consequences concerned in the steam explosion consequence analysis can be obtained, which can make the analysis results closer to reality.

[0006] Furthermore, in some embodiments, the initial physical conditions include a combination of one or more of the following: melt jet diameter, melt temperature, initial water level, initial water temperature, trigger time, and system initial pressure. During a steam explosion, the injection volume and injection rate of the melt significantly influence the severity of the steam explosion, so the melt jet diameter is a key influencing factor. The higher the initial melt temperature, the more severe the consequences of the steam explosion, so the melt temperature is also a key influencing factor. During an in-core steam explosion, the water level in the lower chamber of the reactor pressure vessel determines the amount of water in the steam explosion, while the amount of water in an out-of-core steam explosion is determined by the reactor cavity water level at the time of reactor pressure vessel failure. Therefore, the initial water level (the water level in the lower chamber of the pressure vessel and the reactor cavity) is also a key factor in the steam explosion. Because the water in the lower chamber or the reactor cavity may be undercooled, and the water temperature affects the fragmentation and granulation of the melt, the initial water temperature is also a key influencing factor. Furthermore, the initial system pressure also has a significant impact on the steam explosion process.

[0007] Furthermore, in some embodiments, the probability distribution type includes: uniform distribution, polynomial distribution or step distribution; wherein, when the probability distribution type is uniform distribution, the distribution parameters are the upper and lower bounds of the uniform distribution parameters; when the probability distribution type is polynomial distribution, the distribution parameters are polynomial coefficients; when the probability distribution type is step distribution, the distribution parameters are the upper and lower bounds of the step distribution parameters, the number of segments, the value of each segment and the separation point.

[0008] Furthermore, in some embodiments, the automatic sampling is written in C++, Fortran or Python.

[0009] Furthermore, in some embodiments, the sampling times in the automatic sampling of each parameter is set to 1 to 100 times.

[0010] Furthermore, in some embodiments, the steam explosion consequences include pressure peaks and pressure pulse values.

[0011] Furthermore, in some embodiments, the method further includes the step of calculating the cumulative probability distribution results of the pressure peak value and the pressure pulse value.

[0012] Furthermore, in some embodiments, the method also includes the step of giving a probability threshold and then determining the upper limit value when the cumulative probability of the pressure peak and / or pressure pulse value does not exceed the probability threshold, or giving a threshold of the pressure peak and / or pressure pulse and then determining the cumulative probability when the pressure peak and / or pressure pulse does not exceed the threshold.

[0013] According to an embodiment of another aspect of the present invention, a computing device is provided, which includes a memory and a processor, wherein the memory stores a computing program, and when the processor executes the computing program, it can execute the sampling-based steam explosion consequence analysis method provided in any of the aforementioned embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of pressure peak probability density distribution results in one embodiment;

[0015] Figure 2 A schematic diagram of the cumulative probability distribution of peak pressure in one embodiment;

[0016] Figure 3 Schematic diagram of pressure pulse probability density distribution results in one embodiment;

[0017] Figure 4 Schematic diagram of the cumulative probability distribution of pressure pulses in one embodiment.

[0018] The purpose of the above drawings is to provide a detailed description of the present invention so that those skilled in the art can understand the technical concept of the present invention, and is not intended to limit the present invention. DETAILED DESCRIPTION

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

[0020] Reference to "embodiments" herein means that the specific features, structures, or characteristics described in conjunction with the embodiments may be included in at least one embodiment herein. The phrases appearing in various locations in the specification do not necessarily refer to the same embodiment, nor are they limited to mutually exclusive independent or alternative embodiments. It should be understood by those skilled in the art that the embodiments herein may be combined with other embodiments without causing structural conflicts. In the description herein, "a plurality" means at least two.

[0021] Currently, the consequence analysis of steam explosions in nuclear power plants mostly adopts conservative values ​​for a series of influencing factors and then superimposes predictions. This assessment method can only be used as a reference for engineering design. It is difficult to provide valuable guidance when conducting safety analysis of nuclear power plants and evaluating the actual consequences of accidents of different severities.

[0022] To address the above-mentioned problems, an embodiment of one aspect of the present invention provides a sampling-based steam explosion consequence analysis method, which covers the variation range of key influencing factors through large-scale sampling, making the analysis results more comprehensive; by combining an automatic sampling program with an existing steam explosion analysis simulation program, automatic sampling, automatic generation / reading of input cards, and automatic calculation and analysis are achieved, thereby improving the efficiency of steam explosion consequence analysis; by introducing a probabilistic analysis method, the probability distribution of steam explosion consequences is obtained, making the analysis results closer to the actual situation.

[0023] Specifically, the method comprises the following steps:

[0024] First, based on the analysis results and regularity conclusions of steam explosions, combined with existing steam explosion research, key factors influencing steam explosion consequences were identified and selected as initial physical conditions. Based on the results of typical severe accident sequences and engineering experience, the input probability distribution of each key influencing factor was determined. In a preferred embodiment, the key influencing factors include one or more combinations of melt jet diameter, melt temperature, initial water level, initial water temperature, trigger time, and initial system pressure.

[0025] Next, use the automatic sampling program to automatically sample each key influencing factor and generate an input card. Specifically, the basic logic of the sampling process is to determine the number of parameters involved in the sampling analysis, the probability distribution of the parameters, and the number of samplings based on the information input by the user, and then carry out successive calculations. After each calculation, a result file for a single case is generated and the parameters of interest are output. After the sampling is completed, the probability distribution of the parameters of interest is generated. When sampling, the sampling parameter S is turned on. When S is 0, the sampling analysis is not carried out. When S is 1, the sampling analysis is carried out. Set the number of variables involved in the sampling analysis to N, and set the variable serial number i, such as setting 1 to represent the jet diameter, 2 to represent the melt temperature, 3 to represent the coolant temperature, 4 to represent the air cavity water vapor temperature, 5 to represent the system initial pressure, and 6 to represent the initial water level. For example, when i = 2, 3, it means that the melt temperature and coolant temperature are selected for sampling analysis. Set the number of sampling times to n. The probability distribution P of different variables is set. When P = 1, it is a uniform distribution, and the upper and lower bounds of the uniform distribution parameters need to be given; when P = 2, it is a polynomial distribution, and the polynomial coefficient kn needs to be given; when P = 3, it is a segmented uniform distribution (step distribution), and the upper and lower bounds of the distribution parameters, the number of segments, the value of each segment, and the segmentation point need to be given. Multiple sampling calculations are performed based on the input sampling parameters, and a sampling data file is generated as an input card for the steam explosion analysis program. In various embodiments, the automatic sampling program can be written in a general-purpose programming language such as C++, Fortran, or Python.

[0026] Subsequently, the steam explosion analysis program reads the input card and performs calculations for the pre-mixing, explosion and other stages. Calculations can be automatically continued between each stage. After each calculation, a single case result file is generated and the parameters of interest, such as the steam explosion pressure value and pressure pulse value, are output.

[0027] Furthermore, in a preferred embodiment, after obtaining the probability distribution of the pressure peak value and the pressure pulse value, the cumulative probability distribution can be further obtained, and the failure probability of the containment or reactor pressure vessel can be obtained based on structural mechanics.

[0028] In a preferred embodiment, a sampling-based steam explosion consequence analysis method is provided for a certain type of pressurized water reactor to evaluate the consequences of an out-of-reactor steam explosion.

[0029] First, we screened the key factors and, based on the design and development experience of related reactor types, selected four parameters as key influencing factors: initial melt temperature, initial reactor cavity water level, initial reactor cavity water temperature, and trigger time.

[0030] The initial melt temperature is derived from calculations conducted during severe accident analysis. The uncertainty of the temperature range is then considered, and the probabilities for each temperature range are calculated using a combination of empirical and simulation calculations. For the initial melt temperature range of 1900K-2200K, the probability of 2000K-2100K is 0.6, and the probabilities of 1900K-2000K and 2100K-2200K are 0.2, respectively. For the initial reactor cavity water temperature, the probability of the reactor cavity water temperature being between 330K-390K during IVR (in-core melt pressure vessel retention) is 0.8, and the probability of being between 300K-330K is 0.2. It is generally believed that a flooding failure of the reactor cavity will lead to failure of the IVR and the pressure vessel. Therefore, the probability of the reactor cavity being at a low water level when the pressure vessel fails is relatively high. The elevation of the main coolant pipe is 9.0m, so the probability of the water level being 2.0m-9.0m is relatively high, at 0.8. When the water level in the reactor cavity floods the main coolant pipe, the pressure vessel may still fail due to the heat flux of the molten pool in the lower head of the pressure vessel exceeding the heat exchange limit of the vessel wall, but this probability is relatively small. Therefore, the probability of the initial reactor cavity water level being 9.0m-12.0m is 0.1, and the probability of an extremely low water level of 0-2.0m is 0.1. The triggering time is the time from the premixing stage of the steam explosion to the explosion. After the core molten material flows out of the pressure vessel, it is more likely to be triggered when it contacts the space between the reactor cavity side wall and the bottom plate. Therefore, according to the results of the severe accident analysis, the probability of triggering when the molten material contacts the reactor cavity side wall (0.3s-0.5s) is 0.3, the probability of triggering when it contacts the reactor cavity bottom plate (0.8s-1s) is 0.3, and the probability of triggering between the two (0.5s-0.8s) is 0.4.

[0031] An automatic sampling program is written in C++, Fortran or Python to automatically sample the above four key parameters and generate the input card required by the steam explosion analysis software. The steam explosion analysis software automatically reads the input card and simulates and calculates the specific processes of the mixing stage and the explosion stage, and outputs the data of the explosion consequences. In the preferred embodiment, the explosion consequences are specifically the pressure peak and pressure pulse values. The amount of automatic sampling data is determined according to the computing power, and is usually set to extract 1-100 times for each parameter. In the preferred embodiment, each parameter of the pressurized water reactor is sampled 10 times, and finally 10,000 pressure peak and pressure pulse results are obtained. The pressure peak probability distribution is as follows Figure 1 As shown, it can be seen that the pressure peak is mainly distributed in 40MPa-110MPa. In the preferred embodiment, the cumulative probability distribution of the pressure peak is further obtained as follows Figure 2 As shown in Figure 2, it can be seen that the probability of the pressure peak being less than 110 MPa is above 90%. The probability distribution of the pressure pulse is shown in Figure 2. Figure 3 As shown, it can be seen that the pressure pulse is mainly distributed in the range of 0.12MPa·s-0.3MPa·s. In the preferred embodiment, the cumulative probability distribution of the pressure pulse is further obtained as follows: Figure 4 As shown, the probability that the pressure pulse is less than 0.3 MPa·s is greater than 90%. That is, taking 90% as the probability threshold, the upper limit of the pressure peak is about 110 MPa and the upper limit of the pressure pulse is about 0.3 MPa·s.

[0032] In other embodiments, a threshold value of the pressure peak value and / or pressure pulse may be given, and the cumulative probability value when the pressure peak value and / or pressure pulse does not exceed the threshold value may be determined based on the simulation calculation results.

[0033] Through the above process, an intuitive probability distribution of the consequences of steam explosions can be obtained, providing a clear reference for the safety design of nuclear power plants and the prediction and assessment of accident consequences. Compared with conservative deterministic methods, it can more accurately simulate the state after an actual accident.

[0034] The above embodiment analyzes and simulates the explosion outside the pile. In other embodiments, the above method can also be used to perform analysis and simulation of the explosion inside the pile after adaptive adjustment.

[0035] Another embodiment of the present invention provides a computing device, which can be a general-purpose computer, a dedicated analog computing device such as a single-chip microcomputer, a cloud computing device, or a dedicated server. The computing device includes a memory and a processor. The memory stores a computing program. When the computing program is executed by the processor, it can implement the sampling-based steam explosion consequence analysis method provided in the aforementioned embodiments.

[0036] The purpose of the above embodiments is to further explain the present invention in detail so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, optimization or equivalent replacement of the method steps involved, as well as combination of implementation methods in different embodiments without conflict of structure and principle, all fall within the scope of protection of the present invention.

Claims

1. A method for analyzing the consequences of a steam explosion based on sampling, characterized in that: The following steps are involved: Provide the initial physical conditions of steam explosion and the corresponding input probability distribution; The initial physical conditions are automatically sampled based on the input probability distribution and an input card is generated, wherein the automatic sampling process includes the following steps: providing the number of variables involved in the sampling analysis, the number of sampling times, the variable probability distribution type and the corresponding distribution parameters, sampling and outputting the sampling results; wherein the initial physical conditions include a combination of one or more of the melt jet diameter, melt temperature, initial water level, initial water temperature, trigger time and system initial pressure; wherein the probability distribution type includes: uniform distribution, polynomial distribution or step distribution; wherein, when the probability distribution type is uniform distribution, the distribution parameters are the upper and lower bounds of the uniform distribution parameters; when the probability distribution type is polynomial distribution, the distribution parameters are the polynomial coefficients; when the probability distribution type is step distribution, the distribution parameters are the upper and lower bounds of the step distribution parameters, the number of segments, the value of each segment and the separation point; The data from the input card are respectively used to perform simulation analysis of the steam explosion process, and the probability distribution of the steam explosion consequences is calculated, wherein the steam explosion consequences include pressure peak values and pressure pulse values.

2. The method for analyzing the consequences of steam explosions based on sampling according to claim 1, wherein: The automatic sampling is written in C++, Fortran or Python.

3. The method for analyzing the consequences of steam explosions based on sampling according to claim 1, wherein: The sampling times of each variable in the automatic sampling is set to 1 to 100 times.

4. The method for analyzing the consequences of steam explosions based on sampling according to claim 1, wherein: The method also includes the step of calculating the cumulative probability distribution results of the pressure peak value and the pressure pulse value.

5. The method for analyzing the consequences of steam explosions based on sampling according to claim 4, wherein: It also includes the steps of giving a probability threshold and then determining the upper limit value when the cumulative probability of the pressure peak and / or pressure pulse value does not exceed the probability threshold, or giving a pressure and / or pressure pulse threshold and then determining the cumulative probability when the pressure peak and / or pressure pulse does not exceed the threshold.

6. A computing device comprising a memory and a processor, characterized in that: The memory stores a calculation program, and when the processor executes the calculation program, the sampling-based steam explosion consequence analysis method according to any one of claims 1 to 5 can be executed.

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