Lumped parameter and three-dimensional simulation combined hydrogen risk simulation method and calculation device

Abstract

The invention discloses a lumped parameter and three-dimensional simulation combined hydrogen risk simulation method and a calculation device, and belongs to the field of nuclear power. The lumped parameter and three-dimensional simulation combined hydrogen risk simulation method comprises the following steps: providing an accident sequence, analyzing according to a lumped parameter analysis program to obtain a fluid state function in a containment, and establishing a three-dimensional analysis model of a containment risk area, combining with the one-dimensional analysis model of the lumped parameters of the non-risk region to obtain a combined analysis model; a fluid distribution field is obtained through calculation by means of the conjoint analysis model, and hydrogen risk analysis is conducted. According to the method, the model complexity and workload of hydrogen risk analogue simulation calculation are effectively reduced, and the calculation efficiency is effectively improved on the premise of ensuring the analogue simulation precision.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear power, and specifically relates to a lumped parameter and three-dimensional simulation combined hydrogen risk simulation method and a calculation device. Background Art

[0002] In the event of a hypothetical severe accident at a nuclear power plant, the oxidation of the reactor fuel cladding will produce a large amount of hydrogen. The rapid release of hydrogen in a short period of time may cause a high hydrogen concentration in local areas of the containment. In the later stages of the accident, the reaction between the molten core and the concrete floor will also continuously release flammable gases such as hydrogen and carbon monoxide for a long time, and the total hydrogen concentration in the containment will gradually increase. The accumulation of hydrogen may cause deflagration or explosion, and the resulting temperature or pressure loads may threaten the availability of equipment in the containment and the integrity of the containment. Therefore, analyzing the hydrogen risk in nuclear power plants is very important for the safety management of nuclear power plants.

[0003] Patent CN116956661A discloses a method for simulating hydrogen risk in a containment under a severe reactor accident. It uses severe accident data acquisition and analysis software to carry out accident process analysis to obtain source term parameters required for three-dimensional analysis, and conducts three-dimensional modeling and hydrogen risk analysis on the entire containment. However, the containment of a nuclear power plant has a large spatial size and a complex internal structure. The overall three-dimensional modeling project is huge, and the simulation analysis consumes a lot of time and resources, which is not conducive to improving the safety management level of nuclear power plants.

[0004] Therefore, providing an efficiency-optimized hydrogen risk simulation method has positive significance for hydrogen risk assessment, safety design, and verification optimization of nuclear power plants. Summary of the invention

[0005] The purpose of the present invention is to provide a hydrogen risk simulation method combining lumped parameters and three-dimensional simulation to improve the calculation efficiency of hydrogen risk assessment. The present invention also provides a calculation device.

[0006] According to an embodiment of one aspect of the present invention, a method for simulating hydrogen risk by combining lumped parameters and three-dimensional simulation is provided, the method comprising the following steps:

[0007] Step a): providing an accident sequence, and using a lumped parameter analysis program to simulate and analyze the accident sequence;

[0008] Step b): according to the simulation analysis result of step a), a fluid state function of the fluid parameters in the containment with respect to time is obtained, wherein the fluid state function includes fluid composition, temperature and pressure of the fluid;

[0009] Step c): providing a containment risk area, establishing a three-dimensional analysis model of the risk area, connecting the three-dimensional analysis model with a lumped parameter one-dimensional analysis model of a non-risk area, and obtaining a joint analysis model including the three-dimensional analysis model and the one-dimensional analysis model;

[0010] Step d): According to the fluid state function provided in step b), hydrogen source term data, initial conditions and boundary conditions are provided to the joint analysis model to calculate the fluid distribution field;

[0011] Step e): Perform hydrogen risk assessment based on the fluid distribution field calculated in step d).

[0012] Through this method, accident scenes can be modeled and analyzed in a targeted manner, unnecessary three-dimensional analysis workload can be reduced, computing efficiency can be improved, computing resource consumption can be reduced, and the simulation process can be simplified.

[0013] Furthermore, in some embodiments, the accident sequence in step a) is obtained through PSA analysis of a nuclear power plant.

[0014] Furthermore, in some embodiments, the accident sequence in step a) includes rupture accidents and non-rupture accidents, wherein the rupture accidents include main pipeline rupture accidents, injection pipe rupture accidents and reactor pressure vessel rupture accidents.

[0015] Furthermore, in some embodiments, the fluid in step b) includes hydrogen, water vapor and water released from a circuit.

[0016] Furthermore, in some embodiments, in the step b), the fluid state function also includes the amount of hydrogen released and the rate of hydrogen release.

[0017] Furthermore, in some embodiments, in the step c), the three-dimensional analysis model and the one-dimensional analysis model in the joint analysis model are connected via a flow channel connection model.

[0018] Furthermore, in some embodiments, in the step c), the risk area includes a spatial area where the pipeline rupture in the accident sequence is located.

[0019] Furthermore, in some embodiments, in step e), performing hydrogen risk assessment includes calculating the possibility of flame acceleration using the σ criterion, and calculating the possibility of combustion-explosion transition using the λ criterion.

[0020] Furthermore, in some embodiments, the calculation method of the σ criterion is:

[0021]

[0022] Among them, σ index is the flame acceleration criterion number, σ is the expansion rate of the combustible mixed gas, x is the volume fraction of the gas, and T is the gas temperature;

[0023] The calculation method of the λ criterion is:

[0024]

[0025] D ≥ 7λ,

[0026] Wherein, D is the characteristic dimension of the analyzed compartment, V is the volume of the analyzed compartment, and H is the height of the analyzed compartment.

[0027] 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 computing program is executed by the processor, the lumped parameter and three-dimensional simulation combined hydrogen risk simulation method provided in any of the aforementioned embodiments can be implemented. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of a hydrogen risk simulation method flow in one embodiment;

[0029] Figure 2 A schematic diagram of a joint analysis model in an embodiment;

[0030] Figure 3 This is a schematic diagram of the hydrogen distribution field in the compartment where the breach is located in one embodiment;

[0031] Figure 4 This is a cross-sectional view of the hydrogen distribution field in the compartment where the breach is located in one embodiment.

[0032] The purpose of the above drawings is to explain the present invention in detail so that those skilled in the art can understand the technical concept of the present invention, but it is not intended to limit the present invention. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0034] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The phrase appearing in various locations in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments herein may be combined with other embodiments without causing structural conflicts.

[0035] In the description of this article, the terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating relative importance or limiting the quantity, specific order or primary and secondary relationship of the described technical features. In the description of this article, the meaning of "plurality" is at least two.

[0036] In the event of a hypothetical severe accident at a nuclear power plant, oxidation of the reactor fuel cladding will produce a large amount of hydrogen. The rapid release of hydrogen in a short period of time may cause a high hydrogen concentration in a local area of ​​the containment. In the later stages of the accident, the reaction between the molten core and the concrete floor will also continuously release flammable gases such as hydrogen and carbon monoxide for a long time, and the total hydrogen concentration in the containment will gradually increase. The accumulation of hydrogen may cause deflagration or explosion, and the resulting temperature or pressure loads may threaten the availability of equipment in the containment and the integrity of the containment.

[0037] The mainstream hydrogen risk analysis methods and tools in the current nuclear power industry can be divided into two categories: lumped parameter analysis methods using one-dimensional program tools and three-dimensional analysis methods using computational fluid dynamics analysis tools. The lumped parameter analysis method has the advantages of rich industrial practice, mature models, fast calculation speed, and high analysis efficiency. However, due to its relatively simplified model, this type of method has great limitations. It cannot simulate important phenomena of concern to nuclear power plants such as deflagration, flame acceleration, and combustion-explosion transition. It also cannot solve the problem of whether there is a risk of localized hydrogen accumulation in the containment of nuclear power plants, which is a key concern of the nuclear energy industry after the Fukushima nuclear accident in Japan. The three-dimensional analysis method can simulate the complex hydrogen behavior in the containment of a nuclear power plant and obtain detailed distribution and flow information of hydrogen in the containment. However, limited by the current technological development, the three-dimensional simulation method also has the disadvantages of large computing resource requirements and long computing time.

[0038] In order to overcome the above shortcomings, an embodiment of one aspect of the present invention provides a hydrogen risk simulation method combining lumped parameters and three-dimensional simulation, which can effectively optimize the simulation calculation efficiency while ensuring the simulation accuracy.

[0039] This method is Figure 1 As shown, the following steps are included:

[0040] Step a): First, select and analyze severe accident sequences. In a preferred embodiment, based on the analysis results of the first-level PSA (probabilistic safety assessment) of the target power plant, combined with determinism and engineering judgment, a list of severe accident sequences that require hydrogen risk analysis can be determined, and the selection criteria include factors such as in-pile hydrogen production, hydrogen production rate, hydrogen release location, and hydrogen release flow rate. An integrated lumped parameter analysis program is used to carry out simulation analysis of severe accident sequences. Usually, accident sequences include breach accidents (large breaches, medium breaches, and small breaches), injection pipe break accidents, and reactor pressure vessel rupture accidents.

[0041] Step b): Based on the analysis results of step a), the flow rate, enthalpy, temperature and pressure of the fluid (including hydrogen, steam and water) released from a circuit rupture or other openings (such as a pressure relief valve, etc.) are obtained, and the hydrogen source term analysis is performed to obtain the fluid state function of these fluid parameters changing with time.

[0042] Step c): Based on the accident consequences or engineering judgment, the risk areas that need to be paid attention to in the simulation are given. The risk area can be a high hydrogen concentration area obtained by lumped parameter analysis, an area where the source term release location is located, or a high-risk location of the containment determined based on engineering experience. On the basis of the lumped parameter analysis model, a three-dimensional analysis model of the risk area is established, and the three-dimensional analysis model and the one-dimensional lumped parameter analysis model are connected through the flow channel connection model, and the whole is used as a joint analysis model for subsequent analysis and simulation.

[0043] Step d): According to the fluid state function obtained in step b), the hydrogen source term data, initial conditions and boundary conditions of the joint analysis model are obtained, and the joint analysis model is used to carry out simulation to obtain the change state of the spatial distribution field of each fluid over time.

[0044] Step e): Based on the calculation results of step d), the hydrogen risk at a given moment is evaluated. Specifically, the flame acceleration possibility is calculated using the σ criterion:

[0045]

[0046] Among them, σ index is the flame acceleration criterion number, σ is the expansion rate of the combustible mixed gas, is the volume fraction of hydrogen, is the volume fraction of water vapor, is the volume fraction of oxygen, and T is the gas temperature.

[0047] When the mixed gas burns and meets certain conditions in space, the transition from deflagration to explosion may occur. The λ criterion is used to calculate the possibility of combustion-explosion transition:

[0048]

[0049] D ≥ 7λ,

[0050] Where D is the characteristic dimension of the compartment being analyzed, V is the volume of the compartment, and H is the height of the compartment.

[0051] Based on the above calculation results, the overall evaluation results of hydrogen risk in the containment of a nuclear power plant under a given accident sequence can be obtained. Since there is no need to perform a complete three-dimensional modeling of the entire containment, this method effectively reduces the amount of simulation calculations; at the same time, during the simulation calculation of the joint analysis model, the three-dimensional model of the risk area and the one-dimensional analysis model of the non-risk area are connected through the flow channel model, which can realize the interaction process of mass and energy in the risk area and the non-risk area. Compared with the simulation of three-dimensional modeling with fixed boundary conditions for the risk area only, the accuracy of the simulation has been significantly improved.

[0052] The above-mentioned hydrogen risk simulation method can be implemented by a computing device provided by an embodiment of another aspect of the present invention. The computing device includes a memory and a processor. The memory stores a hydrogen risk simulation calculation program. When the hydrogen risk simulation calculation program is executed by the processor, the lumped parameter and three-dimensional simulation combined hydrogen risk simulation method provided by the above-mentioned embodiment can be implemented. Specifically, the computing device can use a general-purpose computer, or a specially built dedicated computing device, or a cloud computing device or a virtual machine. The hydrogen risk simulation calculation program can be written based on a general-purpose computer language, or it can be written and designed based on a general-purpose CFD software.

[0053] In a preferred embodiment, a large passive pressurized water reactor nuclear power plant is used as the analysis object to conduct hydrogen risk assessment, and the process is as follows:

[0054] Step 1: Use the method of "determinism + probability theory + engineering judgment" to select severe accident sequences. For passive pressurized water reactor nuclear power plants, evaluate the analysis results of the first-level PSA (probabilistic safety assessment) and the contribution of related accident categories to CDF (core damage frequency). The main contribution of CDF comes from loss of coolant accidents (including large, medium and small LOCA accidents, injection pipe break accidents and reactor pressure vessel rupture accidents). For accident sequences that cause containment bypass, it is considered that the containment bypass fails and is not considered in the containment hydrogen analysis.

[0055] In one embodiment, the reactor pressure vessel direct injection line (DVI) rupture accident sequence for hydrogen analysis is shown in Table 1.

[0056]

[0057] Table 1DVI pipeline rupture accident sequence

[0058] Step 2: Use the lumped parameter analysis program to establish an integrated analysis model for a passive pressurized water reactor nuclear power plant, and conduct simulation analysis on the accident sequence determined in step 1. The lumped parameter program passive pressurized water reactor nuclear power plant model covers the reactor coolant system and the containment, and its analysis results can provide the main accident process, the thermal hydraulic response of the primary circuit, and the containment response. For hydrogen analysis, the lumped parameter program analysis results provide key information such as the core oxidation hydrogen production, hydrogen production rate, and the volume fraction (average concentration) of hydrogen / water vapor / oxygen in the main compartments of the containment over time, which can be used as input for subsequent hydrogen risk assessment.

[0059] Step 3: Establish a combined hydrogen risk assessment model of lumped parameters and three-dimensional simulation. For the DVI pipeline breach accident sequence analyzed, the breach area is the key focus area of ​​hydrogen risk in the containment. Based on the lumped parameter analysis model, the control body corresponding to the breach area is established as a local three-dimensional analysis model, and the rest continues to use the one-dimensional model of the lumped parameter analysis program, and the flow channel connection mode between the three-dimensional analysis model control body and other one-dimensional model control bodies is adaptively adjusted to establish a joint analysis model, such as Figure 2 shown.

[0060] Step 4: Based on the joint analysis model, according to the results obtained in step 2, input the source data, boundary conditions and initial conditions of the joint analysis model, carry out simulation calculations, and obtain the following Figure 3 The hydrogen distribution field in the compartment where the breach is located at a given time is shown, or Figure 4 A cross-sectional diagram of the hydrogen distribution field in the compartment at a given moment is shown; similarly, the joint analysis model can calculate the distribution field of other fluids such as oxygen and water vapor in the compartment where the breach is located at a given moment.

[0061] Step 5: Based on the calculation results of step 4, the possibility of flame acceleration is calculated using the σ criterion, and the possibility of combustion-explosion transition is calculated using the λ criterion, and the σ value and λ value at any time in the compartment where the breach is located are obtained respectively.

[0062] Through calculation and analysis, it was found that under the simulated working conditions, the hydrogen concentration in the upper area of ​​the compartment where the breach is located is higher and the hydrogen concentration in the lower area is lower. Since a large amount of water vapor enters the limited space of the compartment through the breach, the water vapor concentration is very high and the oxygen concentration is very low. There is no risk of hydrogen combustion in this risk area.

[0063] The lumped parameter and three-dimensional simulation combined hydrogen risk simulation method provided in the above embodiment has the following advantages: the method can be used to establish a three-dimensional analysis model for the local area of ​​the containment of a nuclear power plant, simulate the complex hydrogen flow and distribution behavior in the key area of ​​the containment, and solve the hydrogen risk problem in the local area of ​​the containment; it can be used to establish a common water pool model in the containment of a nuclear power plant, simulate evaporation, condensation and water level changes, and more realistically simulate the thermal hydraulic phenomena in the containment of a nuclear power plant; the calculation efficiency is high, the consumption of computing resources is small, and the calculation time is short, which is suitable for modeling and analysis of simulation objects with both large free volume and complex geometric structure characteristics; the model is concise, the modeling method is simple, the model is easy to build, and it is user-friendly.

[0064] The purpose of the above embodiments is to further explain the present invention in detail in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, the optimization or equivalent replacement of the method steps involved, and the combination of the implementation methods in different embodiments without conflict of structure and principle, all fall within the protection scope of the present invention.

Claims

1. A lumped parameter and three-dimensional simulation combined hydrogen risk simulation method, characterized in that: The following steps are involved: Step a): providing an accident sequence, and using a lumped parameter analysis program to simulate and analyze the accident sequence; Step b): according to the simulation analysis result of step a), a fluid state function of the fluid parameters in the containment with respect to time is obtained, wherein the fluid state function includes fluid composition, temperature and pressure of the fluid; Step c): providing a containment risk area, establishing a three-dimensional analysis model of the risk area, connecting the three-dimensional analysis model with a lumped parameter one-dimensional analysis model of a non-risk area, and obtaining a joint analysis model including the three-dimensional analysis model and the one-dimensional analysis model; Step d): According to the fluid state function provided in step b), hydrogen source term data, initial conditions and boundary conditions are provided to the joint analysis model to calculate the fluid distribution field; Step e): Perform hydrogen risk assessment based on the fluid distribution field calculated in step d).

2. The lumped parameter and three-dimensional simulation combined hydrogen risk simulation method according to claim 1 is characterized in that: The accident sequence in step a) is obtained through PSA analysis of a nuclear power plant.

3. The method for simulating hydrogen risk by combining lumped parameters and three-dimensional simulation according to claim 1 or 2, characterized in that: The accident sequence in step a) includes rupture accidents and non-rupture accidents, wherein the rupture accidents include main pipeline rupture accidents, injection pipe rupture accidents and reactor pressure vessel rupture accidents.

4. The method for hydrogen risk simulation combining lumped parameters and three-dimensional simulation according to claim 1 is characterized in that: The fluid in step b) includes hydrogen, water vapor and water released from a circuit.

5. The method for hydrogen risk simulation combining lumped parameters and three-dimensional simulation according to claim 4 is characterized in that: In the step b), the fluid state function also includes the amount of hydrogen released and the hydrogen release rate.

6. The method for hydrogen risk simulation combining lumped parameters and three-dimensional simulation according to claim 1 is characterized in that: In the step c), the three-dimensional analysis model and the one-dimensional analysis model in the joint analysis model are connected via a flow channel connection model.

7. The method for hydrogen risk simulation combining lumped parameters and three-dimensional simulation according to claim 6 is characterized in that: In the step c), the risk area includes the spatial area where the pipeline rupture in the accident sequence is located.

8. The method for hydrogen risk simulation combining lumped parameters and three-dimensional simulation according to claim 1 is characterized in that: In the step e), the hydrogen risk assessment includes calculating the possibility of flame acceleration using the σ criterion and calculating the possibility of explosion transition using the λ criterion.

9. The method for hydrogen risk simulation combining lumped parameters and three-dimensional simulation according to claim 8 is characterized in that: The calculation method of the σ criterion is: Among them, σ index is the flame acceleration criterion number, σ is the expansion rate of the combustible mixed gas, x is the volume fraction of the gas, and T is the gas temperature; The calculation method of the λ criterion is: D ≥ 7λ, Wherein, D is the characteristic dimension of the analyzed compartment, V is the volume of the analyzed compartment, and H is the height of the analyzed compartment.

10. A computing device, comprising a memory and a processor, characterized in that: The memory stores a calculation program, and when the calculation program is executed by the processor, the lumped parameter and three-dimensional simulation combined hydrogen risk simulation method as described in any one of claims 1 to 9 can be implemented.

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