A method and system for assessing the safety of structures penetrated by hydrogen diffusion flames

Abstract

This disclosure relates to the technical field of nuclear reactor operational safety assessment. It proposes a method and system for assessing the safety of structures penetrated by hydrogen diffusion flames. This method assesses the impact of hydrogen diffusion flames on steel containment structures during severe reactor accidents. By rationally simulating hydrogen diffusion flames during severe reactor accidents, the consequences of hydrogen diffusion flames are evaluated, thereby assessing the integrity of steel containment structures penetrated by them. This method is suitable for assessing the consequences of hydrogen diffusion flames in passive nuclear power plants and can effectively evaluate the integrity of containment structures penetrated by hydrogen diffusion flames.

Description

Technical Field

[0001] The present disclosure relates to the technical field related to nuclear reactor operation safety assessment, and more specifically, to a method and system for assessing the safety of a structure penetrated by a hydrogen diffusion flame, which can be used for assessing the safety of a containment structure penetrated by a nuclear reactor under the action of a hydrogen diffusion flame. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.

[0003] In the event of a severe accident, oxidation of the reactor fuel cladding will produce large quantities of hydrogen. When hydrogen within the containment diffuses from confined compartments into the larger space, the abundant oxygen in this larger space can easily generate a hydrogen diffusion flame. This hydrogen diffusion flame exerts strong radiative heat on the nearby steel containment walls and penetrations (including electrical penetrations, equipment gates, and personnel gates). Under this intense radiative heat, these components may experience creep failure or loss of integrity. This is especially true for containment areas with numerous penetrations, where the integrity of these penetrations must be ensured in the event of a severe accident. Due to recent nuclear leak accidents, the international community has heightened concern about the risks of hydrogen within nuclear power plant containment, placing higher demands on the reliability and diversity of hydrogen control systems in nuclear power plants. During the safety review process for domestic nuclear power plant projects, reviewers also place significant emphasis on hydrogen risk analysis.

[0004] A key feature of passive nuclear power plants (such as CAP1400 and CAP1000) is their steel containment, which is equipped with numerous penetrations, including electrical penetrations, equipment gates, and personnel gates. When a hydrogen diffusion flame occurs in a confined compartment, it exerts a strong radiative heat transfer effect on the steel containment walls and the penetrations. Excessive temperatures within the penetrations can lead to failure of the penetrations, translating to containment failure and potentially releasing large amounts of radioactive material into the environment. Therefore, research on the safety assessment of containment is of vital importance. Summary of the Invention

[0005] To address the aforementioned issues, this disclosure proposes a method and system for assessing the safety of structures penetrated by hydrogen diffusion flames. This method evaluates the impact of hydrogen diffusion flames on steel containment structures during severe reactor accidents. By rationally simulating hydrogen diffusion flames during severe reactor accidents, the consequences of hydrogen diffusion flames are evaluated, thereby assessing the integrity of steel containment structures penetrated by them. This method is suitable for assessing the consequences of hydrogen diffusion flames in passive nuclear power plants and can effectively assess the integrity of containment structures penetrated by hydrogen diffusion flames.

[0006] In order to achieve the above objectives, the present disclosure adopts the following technical solutions:

[0007] One or more embodiments provide a method for assessing the safety of a structure penetrated by a hydrogen diffusion flame, comprising the following steps:

[0008] Equivalent the diffusion flame to a geometric body and calculate the flame height based on the environmental conditions under which the accident occurs;

[0009] Calculate the hot spot angle coefficient of the inner wall of the steel containment and the angle coefficient of the flame penetrating the containment structure to obtain the radiation heat transfer angle coefficient;

[0010] Calculate the hot spot temperature of the inner wall of a steel containment vessel under the action of a diffusion flame;

[0011] Based on the calculated hot spot temperature of the containment inner wall and the radiation heat transfer angular coefficient, the established transient heat transfer differential equation of the penetrating structure is solved to obtain the temperature of the containment penetrating structure wall and the air cavity;

[0012] Based on the temperature of the containment penetration structure wall and the air cavity, it is determined whether the containment penetration structure can remain intact under the action of the diffusion flame, and the safety assessment result is obtained.

[0013] One or more embodiments provide a system for assessing the safety of structures penetrated by hydrogen diffusion flames, including:

[0014] Equivalent module: It is configured to equate the diffusion flame to a geometric body and calculate the flame height based on the environmental conditions under the accident;

[0015] Radiation heat transfer angular coefficient calculation module: configured to calculate the hot spot angular coefficient of the inner wall of the steel containment and the angular coefficient of the flame penetrating the containment structure to obtain the radiation heat transfer angular coefficient;

[0016] Radiation heat transfer angular coefficient calculation module: configured to calculate the hot spot temperature of the inner wall of the steel containment under the action of diffusion flame;

[0017] Temperature solver module: This module is configured to solve the established transient heat transfer differential equation for the penetrating structure based on the calculated hot spot temperature of the containment inner wall and the radiation heat transfer angular coefficient, and obtain the temperature of the containment penetrating structure wall and the air cavity;

[0018] Evaluation module: configured to determine whether the containment penetration structure can remain intact under the action of the diffusion flame based on the temperature of the containment penetration structure wall and the air cavity, and obtain a safety evaluation result.

[0019] An electronic device includes a memory and a processor, and computer instructions stored in the memory and executed on the processor. When the computer instructions are executed by the processor, the steps of the above method are completed.

[0020] A computer-readable storage medium is used to store computer instructions, and when the computer instructions are executed by a processor, the steps of the above method are completed.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] In the present disclosure, the diffusion flame is equivalently treated by obtaining the flame generation environmental conditions, and the positional relationship between the heat radiated object and the flame is reasonably assumed, thereby obtaining an accurate radiation heat transfer angular coefficient, thereby improving the accuracy of the temperature identification of the air cavity of the containment penetration structure, and being able to accurately judge the safety of the containment penetration structure, thereby improving the safety of the reactor operation.

[0023] The advantages of the present disclosure and additional advantages will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which constitute a part of the present disclosure, are used to provide a further understanding of the present disclosure. The exemplary embodiments of the present disclosure and their descriptions are used to explain the present disclosure but do not constitute a limitation of the present disclosure.

[0025] Figure 1 is a flow chart of the security assessment method of Example 1 of the present disclosure;

[0026] FIG2( a ) is a schematic diagram of the diffusion flame radiation heat exchange according to Example 1 of the present disclosure;

[0027] FIG2( b ) is a schematic diagram of a diffusion flame equivalent cylinder according to Example 1 of the present disclosure;

[0028] Figure 3 Schematic diagram of the positions of the steel containment, the middle annular cavity and the concrete wall in Example 1 of the present disclosure;

[0029] Figure 4 This is a schematic diagram of heat transfer of the electrical penetration component of Example 1 of the present disclosure. DETAILED DESCRIPTION

[0030] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0031] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present disclosure belongs.

[0032] It should be noted that the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the exemplary embodiments according to the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof. It should be noted that, in the absence of conflict, the various embodiments in the present disclosure and the features in the embodiments can be combined with each other. The embodiments will be described in detail below with reference to the accompanying drawings.

[0033] Example 1

[0034] In the technical solutions disclosed in one or more embodiments, Figures 1 to 4 As shown, a method for safety assessment of a structure penetrated by a hydrogen diffusion flame is used for safety assessment of a nuclear reactor containment structure penetrated by a hydrogen diffusion flame, comprising the following steps:

[0035] Step 1: Equivalent the diffusion flame to a geometric body and calculate the flame height based on the environmental conditions under which the accident occurs;

[0036] Step 2: Calculate the hot spot angle coefficient of the inner wall of the steel containment and the angle coefficient of the flame penetrating the containment structure to obtain the radiation heat transfer angle coefficient;

[0037] Step 3: Calculate the hot spot temperature of the inner wall of the steel containment under the action of diffusion flame;

[0038] Step 4: Solve the established transient heat transfer equation for the penetrating structure based on the calculated hot spot temperature of the containment inner wall and the radiation heat transfer angular coefficient to obtain the temperature of the containment penetrating structure wall and the air cavity;

[0039] Step 5: Based on the temperature of the containment penetration structure wall and the air cavity, determine whether the containment penetration structure can remain intact under the action of the diffusion flame, and obtain a safety assessment result.

[0040] In this embodiment, the diffusion flame is equivalently treated by obtaining the flame generation environmental conditions, and the positional relationship between the heat radiated object and the flame is reasonably assumed, thereby obtaining an accurate radiation heat transfer angular coefficient, thereby improving the accuracy of the temperature identification of the air cavity of the containment penetration structure, and being able to accurately judge the safety of the containment penetration structure, thereby improving the safety of the reactor operation.

[0041] First, the diffusion flame is equivalently processed and can be equivalent to a geometric body with a similar shape to the flame. Optionally, the equivalent geometric body can be a truncated cone or a cylinder. Preferably, in order to reduce the amount of calculation and improve the calculation efficiency, a cylinder can be selected.

[0042] In this embodiment, it can be applied to the safety assessment of the containment penetration structure under severe accidents. In step 1, based on the environmental conditions under which a severe accident occurs, information such as the hydrogen flow rate at the exhaust port, the heat released by hydrogen combustion, the density of the gas in the containment, the heat capacity of the gas, and the gas temperature can be included.

[0043] The radiation heat transfer angular coefficient is the most important input in the diffusion flame consequence assessment. The radiation heat transfer angular coefficient includes the hot spot angular coefficient of the inner wall of the steel containment and the angular coefficient of the flame to the containment penetration structure. When the containment penetration structure is an electrical penetration, the angular coefficient of the flame to the containment penetration structure can be the electrical penetration angular coefficient.

[0044] In step 2, for the hot spot angle coefficient, the object being heated is considered to be at the center elevation of the flame equivalent cylinder. Figure 2(a) to Figure 2(b) As shown, the diffusion flame is equivalent to a cylinder, which is divided into upper and lower sections. For the hot spot angle coefficient, the object being heated is assumed to be at the center elevation of the cylinder. For the wall of the containment penetration structure, the height of the upper section of the cylinder is assumed to be the vertical height difference between the penetration structure and the top of the diffusion flame. In other words, the boundary between the upper and lower sections of the cylinder is at the same height as the center of the penetration structure. As shown in Figure 2, R refers to the horizontal distance from the center of the flame cylinder to the containment penetration structure, and L refers to the horizontal distance from the outer wall of the flame cylinder to the containment penetration structure.

[0045] In this embodiment, by assuming the positional relationship between the heat radiated object and the diffusion flame equivalent, the heat absorption of the containment penetration structure can be effectively simulated, thereby evaluating the integrity of the containment penetration structure.

[0046] Specifically, the hot spot angle coefficient and the angle coefficient of the electrical penetration wall are calculated using the following formulas (1)-(7):

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053] Electrical penetration angle factor = F V1 +F V2 (7)

[0054] Among them, a and b are related to the flame height, flame size, and the distance between the flame and the evaluation object. That is, when calculating the hot spot angle coefficient, a=H f / D, when calculating the angle coefficient of penetrating structure, a=2H f1 / D or 2H f2 / D,b=2R / D,H f1 is the height of the lower section of the flame equivalent cylinder, H f2 is the height of the upper section of the flame equivalent cylinder, D is the diameter of the flame equivalent cylinder; F V1 、F V2 Refers to the F corresponding to the upper diffusion flame and the lower diffusion flame respectively V .

[0055] In order to evaluate the integrity of the steel containment penetration structure, it is necessary to evaluate the hot spot temperature of the containment inner wall under the action of diffusion flame.

[0056] In step 3, the hot spot temperature of the inner wall of the containment is solved by establishing three thermal balance relationships, namely: the thermal balance relationship of the inner wall of the containment, the thermal balance relationship of the outer wall of the containment, and the thermal balance relationship of the concrete wall. The hot spot temperature of the inner wall of the containment is obtained after solving them jointly.

[0057] Figure 3 Shown is a schematic diagram of the locations of the steel containment, central annular cavity and concrete wall.

[0058] (1) Thermal balance relationship of the inner wall of the containment

[0059] Taking the inner wall of the containment as the research object, the following thermal equilibrium relationship exists: the sum of the radiation heat transfer from the diffusion flame to the inner wall of the containment and the convective heat transfer from the diffusion flame plume to the inner wall of the containment is equal to the heat conduction from the inner wall of the containment to the outer wall of the containment.

[0060] It is specifically expressed as the following relationship:

[0061]

[0062] Where σ is the Boltzmann constant, 5.67×10-8W / (m2·K4);

[0063] ε f is the emissivity of the diffusion flame;

[0064] ε w is the emissivity of the containment;

[0065] T f is the diffusion flame temperature;

[0066] α g is the absorption ratio of the diffuse flame plume;

[0067] Ti is the temperature of the inner wall of the containment (unknown);

[0068] h is the convective heat transfer coefficient from the diffusion flame plume to the inner wall of the containment;

[0069] T air is the temperature of the gas in the compartment, which is the containment area where the diffusion flame is located;

[0070] k s is the thermal conductivity of the containment;

[0071] d is the containment wall thickness;

[0072] T o is the temperature of the outer wall of the containment (an unknown quantity);

[0073] F is the angular coefficient of the diffusion flame to the hot spot of the containment.

[0074] (2) Thermal balance relationship of the containment outer wall

[0075] Taking the outer wall of the containment as the research object, the following thermal equilibrium relationship exists: the sum of the convective heat transfer from the outer wall of the containment to the gas in the central annular cavity and the radiative heat transfer from the outer wall of the containment to the concrete wall is equal to the heat transfer from the inner wall of the containment to the outer wall of the containment. It can be specifically expressed as the following relationship:

[0076]

[0077] Among them, T m is the temperature of the gas in the middle ring cavity;

[0078] ε c is the emissivity of the concrete wall;

[0079] T c is the temperature of the concrete wall (an unknown quantity);

[0080] h i is the natural convection heat transfer coefficient from the outer wall of the containment to the gas in the middle annular cavity, which can be calculated using the following formula:

[0081]

[0082] Where k is the thermal conductivity of air;

[0083] β is the volume expansion coefficient of air;

[0084] ν is the kinematic viscosity of air;

[0085] α is the thermal diffusivity of air.

[0086] (3) Thermal balance relationship of concrete wall

[0087] Taking the concrete wall as the research object, the following thermal equilibrium relationship exists: the convective heat transfer between the concrete wall and the gas in the central annular cavity is equal to the radiative heat transfer from the outer wall of the containment to the concrete wall. This is specifically expressed as the following relationship:

[0088]

[0089] The above three equations (8), (9) and (11) are combined to form an equation system, and the unknown quantity T can be solved. i 、T o and T c , then the hot spot temperature T i It can be obtained.

[0090] In step 4, the containment penetration structure air cavity temperature is determined based on the obtained containment wall hot spot temperature and the radiation heat transfer angular coefficient of the diffusion flame to the containment penetration structure wall.

[0091] Optionally, the temperature of the containment through-structure wall and the air cavity can be obtained by establishing a through-structure transient heat transfer equation and performing a transient solution.

[0092] Figure 4 The figure shows a schematic diagram of heat transfer through the containment structure. Based on the hot spot temperature of the containment wall and the angular coefficient of heat transfer from the diffusion flame to the containment structure wall, the temperature of the electrical penetration wall and the air cavity is calculated using a transient solution method.

[0093] Construct two transient differential equations (12) and (13), which are transient heat transfer equations of penetrating structures, and solve the wall temperature T of the electrical penetration component. s and the air cavity temperature T a .

[0094]

[0095]

[0096] Among them, T s is the wall temperature of the electrical penetration;

[0097] T a is the gas temperature of the electrical penetration cavity;

[0098] T i is the hot spot temperature of the inner wall of the containment;

[0099] α s is the emissivity of the electrical penetration wall;

[0100] T air is the gas temperature in the compartment;

[0101] d sis the wall thickness of the electrical penetration;

[0102] ρ s and c s are the density and specific heat capacity of the electrical penetration material;

[0103] ρ a and c a are the density and specific heat of the gas in the electrical penetration cavity, respectively. Considering that before the electrical penetration loses its integrity, the density of the gas in the cavity remains unchanged, and the change of the specific heat of the gas with temperature can be ignored. Therefore, ρ a and c a The values are taken at normal temperature and 1 atmosphere pressure;

[0104]

[0105]

[0106] A3=πHL;

[0107] h n is the convection heat transfer coefficient between the gas in the compartment and the wall of the electrical penetration, h n (T s ,T a ) is the convection heat transfer coefficient between the wall of the electrical penetration and the air cavity, h n (T a ,T i ) is the convective heat transfer coefficient between the gas cavity and the containment wall, It is the convection heat transfer coefficient between the circumferential wall of the electrical penetration and the air cavity.

[0108] Finally, by judging the air cavity temperature T a Whether the acceptance criterion value is met, the acceptance criterion value can be set to 204°C to evaluate whether the electrical penetration can remain intact, that is, whether the containment penetration structure can remain intact.

[0109] The present disclosure is not strictly limited to the examples described above. The solutions and principles proposed in the present disclosure can be applied to the evaluation of the integrity of other steel containment penetration structures.

[0110] Example 2

[0111] Based on Example 1, this embodiment provides a system for assessing the safety of structures penetrated by hydrogen diffusion flames, including:

[0112] Equivalent module: It is configured to equate the diffusion flame to a geometric body and calculate the flame height based on the environmental conditions under the accident;

[0113] Radiation heat transfer angular coefficient calculation module: configured to calculate the hot spot angular coefficient of the inner wall of the steel containment and the angular coefficient of the flame penetrating the containment structure to obtain the radiation heat transfer angular coefficient;

[0114] Radiation heat transfer angular coefficient calculation module: configured to calculate the hot spot temperature of the inner wall of the steel containment under the action of diffusion flame;

[0115] Temperature solver module: This module is configured to solve the established transient heat transfer differential equation for the penetrating structure based on the calculated hot spot temperature of the containment inner wall and the radiation heat transfer angular coefficient, and obtain the temperature of the containment penetrating structure wall and the air cavity;

[0116] Evaluation module: configured to determine whether the containment penetration structure can remain intact under the action of the diffusion flame based on the temperature of the containment penetration structure wall and the air cavity, and obtain a safety evaluation result.

[0117] It should be noted here that the various modules in this embodiment correspond one-to-one to the various steps in Example 1, and the specific implementation processes are the same, which will not be repeated here.

[0118] Example 3

[0119] This embodiment provides an electronic device, including a memory and a processor, and computer instructions stored in the memory and running on the processor. When the computer instructions are run by the processor, the steps described in the method of embodiment 1 are completed.

[0120] Example 4

[0121] This embodiment provides a computer-readable storage medium for storing computer instructions. When the computer instructions are executed by a processor, the steps described in the method of embodiment 1 are completed.

[0122] The foregoing description is merely a preferred embodiment of the present disclosure and is not intended to limit the present disclosure. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present disclosure shall be included within the scope of protection of the present disclosure.

[0123] Although the above describes the specific implementation methods of the present disclosure in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present disclosure. Those skilled in the art should understand that on the basis of the technical solution of the present disclosure, various modifications or variations that can be made by those skilled in the art without creative work are still within the scope of protection of the present disclosure.

Claims

1. A method for assessing the safety of structures penetrated by hydrogen diffusion flames, characterized in that: The steps include: Equivalent the diffusion flame to a geometric body and calculate the flame height based on the environmental conditions under which the accident occurs; Calculate the hot spot angle coefficient of the inner wall of the steel containment and the angle coefficient of the flame penetrating the containment structure to obtain the radiation heat transfer angle coefficient; Calculate the hot spot temperature of the inner wall of a steel containment vessel under the action of a diffusion flame; Based on the calculated hot spot temperature of the containment inner wall and the radiation heat transfer angular coefficient, the established transient heat transfer differential equation of the penetrating structure is solved to obtain the temperature of the containment penetrating structure wall and the air cavity; Based on the temperature of the containment penetration structure wall and the air cavity, determine whether the containment penetration structure can remain intact under the action of the diffusion flame and obtain the safety assessment result; Establish the thermal balance relationship of the containment inner wall, the thermal balance relationship of the containment outer wall and the thermal balance relationship of the concrete wall, and obtain the hot spot temperature of the containment inner wall after solving them jointly; The heat balance relationship of the containment inner wall is: the sum of the radiation heat transfer from the diffusion flame to the containment inner wall and the convective heat transfer from the diffusion flame plume to the containment inner wall is equal to the heat conduction from the containment inner wall to the containment outer wall; The heat balance relationship of the containment outer wall is: the sum of the convective heat transfer from the containment outer wall to the gas in the middle ring cavity and the radiation heat transfer from the containment outer wall to the concrete wall is equal to the heat conduction from the containment inner wall to the containment outer wall; The thermal balance relationship of the concrete wall is: the convection heat transfer between the concrete wall and the gas in the middle ring cavity is equal to the radiation heat transfer from the outer wall of the containment to the concrete wall.

2. The method for assessing the safety of a structure penetrated by a hydrogen diffusion flame according to claim 1, wherein: The equivalent geometric solids are a frustum or a cylinder.

3. The method for assessing the safety of a structure penetrated by a hydrogen diffusion flame according to claim 1, wherein: The diffusion flame is equivalent to a cylinder, which is divided into two sections, the upper and lower sections. For the hot spot angle coefficient, the object being radiated is considered to be at the center elevation of the cylinder. For the wall of the containment penetrating structure, the height of the upper section of the flame equivalent cylinder is considered to be the vertical height difference between the penetrating structure and the top of the diffusion flame.

4. A safety assessment system for structures penetrated by hydrogen diffusion flames based on the safety assessment method for structures penetrated by hydrogen diffusion flames according to claim 1, characterized in that: include: Equivalent module: It is configured to equate the diffusion flame to a geometric body and calculate the flame height based on the environmental conditions under the accident; Radiation heat transfer angular coefficient calculation module: configured to calculate the hot spot angular coefficient of the inner wall of the steel containment and the angular coefficient of the flame penetrating the containment structure to obtain the radiation heat transfer angular coefficient; Radiation heat transfer angular coefficient calculation module: configured to calculate the hot spot temperature of the inner wall of the steel containment under the action of diffusion flame; Temperature solver module: This module is configured to solve the established transient heat transfer differential equation for the penetrating structure based on the calculated hot spot temperature of the containment inner wall and the radiation heat transfer angular coefficient, and obtain the temperature of the containment penetrating structure wall and the air cavity; Evaluation module: configured to determine whether the containment penetration structure can remain intact under the action of the diffusion flame based on the temperature of the containment penetration structure wall and the air cavity, and obtain a safety evaluation result.

5. An electronic device, characterized in that: The invention comprises a memory and a processor, and computer instructions stored in the memory and executed on the processor. When the computer instructions are executed by the processor, the steps of the method for safety assessment of penetration of a structure under the action of a hydrogen diffusion flame as described in any one of claims 1 to 3 are completed.

6. A computer-readable storage medium, characterized in that Used to store computer instructions, which, when executed by a processor, complete the steps of the method for safety assessment of a structure penetrated by a hydrogen diffusion flame as described in any one of claims 1 to 3.

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