Corrosion evaluation method, corrosion evaluation apparatus, and program

Abstract

To provide a method for accurately evaluating corrosion of a structure by jetting.SOLUTION: A corrosion evaluation method has the steps of: analyzing temporal changes in a temperature and a heat transfer coefficient of a core material; solving a one-dimensional nonsteady heat conduction equation indicating heat conduction in a structure affected by the heat from the core material by using a temperature at an end of the structure based on the temperature and the heat transfer coefficient as a boundary condition, and analyzing a temporal change in the temperature distribution within the structure; and evaluating corrosion of the structure on the basis of a result of analysis of the temperature distribution. In this method, the specific heat in the one-dimensional nonsteady heat conduction equation is set on the basis of a correspondence between enthalpy and the temperature in consideration of the latent heat during melting of the structure, and a sufficiently large value indicating that the heat from the core material does not remain in a molten part is set to the thermal conductivity of the one-dimensional nonsteady heat conduction equation.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an erosion evaluation method, an erosion evaluation device, and a program. [Background technology]

[0002] When a severe accident occurs in a fast reactor, core materials such as fuel and steel are released from the molten core in a jet-like form, and this molten core material (hereafter referred to as the jet) can erode the structures inside the reactor. When analyzing this type of erosion process, it is often assumed that the amount and temperature of the jet released are constant. However, in reality, the amount and temperature of the jet released are not constant, so there are limits to the accuracy of the analysis.

[0003] As a related technique, Patent Document 1 discloses a method for analyzing the coolability of fuel debris accumulated on a core catcher installed below a reactor vessel by solving an unsteady heat conduction equation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6728305 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a demand for technology that can accurately evaluate the erosion of structures caused by jets.

[0006] The present disclosure provides an erosion evaluation method, an erosion evaluation device, and a program that can solve the above problems. [Means for solving the problem]

[0007] The erosion evaluation method according to the present disclosure includes the steps of: analyzing the changes over time in temperature and heat transfer coefficient of core material released from the molten core; analyzing the changes over time in temperature distribution within the structure by solving a one-dimensional unsteady heat conduction equation that indicates the conduction of heat in a structure to which the heat from the released core material is transferred, using the temperature and the temperature of the end of the structure based on the heat transfer coefficient as boundary conditions; and evaluating the erosion of the structure based on the results of the analysis of the temperature distribution. In the step of analyzing the changes over time in temperature distribution within the structure, a specific heat value calculated based on the correspondence between enthalpy and temperature taking into account the latent heat at the time of melting of the structure is set as the specific heat of the one-dimensional unsteady heat conduction equation, and a sufficiently large predetermined value that indicates that the heat from the core material will not remain in the molten part of the structure is set as the thermal conductivity of the one-dimensional unsteady heat conduction equation.

[0008] The erosion evaluation device according to the present disclosure includes a means for analyzing the temporal changes in temperature and heat transfer coefficient of core material released from a molten core, a means for analyzing the temporal changes in temperature distribution within the structure by solving a one-dimensional unsteady heat conduction equation showing the conduction of heat in a structure to which the heat from the released core material is transferred, with the temperature of the end of the structure based on the temperature and the heat transfer coefficient as boundary conditions, and a means for evaluating the erosion of the structure based on the results of the analysis of the temperature distribution, wherein the means for analyzing the temporal changes in temperature distribution within the structure sets the specific heat value of the one-dimensional unsteady heat conduction equation to a corresponding relationship between enthalpy and temperature taking into account the latent heat at the time of melting of the structure, and sets the thermal conductivity of the one-dimensional unsteady heat conduction equation to a sufficiently large predetermined value indicating that the heat from the core material will not remain in the molten part of the structure.

[0009] The program according to the present disclosure has a step of causing a computer to perform a process of analyzing changes over time in temperature and heat transfer coefficient of core material released from a molten core, a step of analyzing changes over time in temperature distribution within the structure by solving a one-dimensional unsteady heat conduction equation that indicates the conduction of heat in a structure to which the heat from the released core material is transferred, using the temperature and the temperature of the end of the structure based on the heat transfer coefficient as boundary conditions, and a step of evaluating erosion of the structure based on the results of the analysis of the temperature distribution, in which the step of analyzing changes over time in temperature distribution within the structure causes a computer to perform a process of setting a specific heat value calculated based on a correspondence between enthalpy and temperature that takes into account the latent heat at the time of melting of the structure to the specific heat of the one-dimensional unsteady heat conduction equation, and setting a sufficiently large predetermined value that indicates that the heat from the core material will not remain in the molten part of the structure to the thermal conductivity of the one-dimensional unsteady heat conduction equation. Effect of the Invention

[0010] According to the erosion evaluation method, erosion evaluation device, and program disclosed herein, erosion of a structure by a jet can be evaluated with high accuracy. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram showing an example of an erosion evaluation device according to an embodiment. [Diagram 2] 1A to 1C are diagrams illustrating an erosion evaluation method according to an embodiment. [Figure 3A] FIG. 4 is a diagram showing an example of an enthalpy-temperature curve used in erosion evaluation according to the embodiment. [Figure 3B] FIG. 11 is a diagram showing an example of thermal conductivity used in erosion evaluation according to the embodiment. [Figure 4] 1 is a flowchart illustrating an example of an erosion evaluation method according to an embodiment. [Diagram 5] FIG. 2 is a diagram illustrating an example of a hardware configuration of the erosion evaluation device according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] <Embodiment> The erosion evaluation method of the present disclosure will be described below with reference to FIGS. (composition) FIG. 1 is a block diagram showing an example of an erosion evaluation device according to an embodiment. The erosion evaluation device 10 analyzes and evaluates the time-dependent change in temperature distribution of a structure caused by the heat of the jet discharged from the molten core, and the erosion depth of the structure. The structure eroded by the jet is, for example, a mitigation structure provided in the reactor. The mitigation structure is a plate-shaped member provided below the core in a fast reactor to reduce the speed of the jet. FIG. 2 shows an example of the mitigation structure 100 and the jet 200. When the core is damaged during a severe accident, the jet 200 is discharged from the core, falls, and is received by the mitigation structure 100. The jet 200 erodes the mitigation structure 100 by heat, and falls downward from a hole 101 provided in the mitigation structure 100 in advance. The speed of the jet passing through the hole 101 is reduced by the mitigation structure 100, and the jet 201 is released from the hole 101. The erosion evaluation device 10 analyzes the temperature distribution and the temporal change in the erosion depth D of the relaxation structure 100 due to the heat from the jet 200 based on a model M that models a predetermined area 102 of the relaxation structure 100. The model M divides the relaxation structure 100 into n layers in the z-axis direction (thickness direction of the relaxation structure 100 or the falling direction of the jet) in FIG. 2, and models the relaxation structure 100 so that the behavior of heat transfer from the top layer to the bottom layer can be analyzed layer by layer, such as the temperature of the top layer 1 rising due to the heat of the jet 200 emitted from above, the heat being transferred from layer 1 to layer 2, and then to layer 3, etc. For example, when the temperature of layer 1 rises and reaches the melting point, layer 1 melts (i.e., is eroded), and the heat from the jet 200 is transferred more directly to layer 2, and then when the temperature of layer 2 reaches the melting point, layer 2 is also eroded. Through this process, the erosion range gradually expands from the top to the bottom of the relaxation structure 100. In this embodiment, a one-dimensional unsteady heat conduction equation is solved for each layer to capture the temperature change of the relaxation structure 100 by layer, thereby analyzing the temporal change in temperature distribution of the entire relaxation structure 100. Then, based on the evaluated temperature distribution, a layer whose temperature has reached its melting point is evaluated as being eroded, and the erosion depth D is evaluated.

[0013] As shown in FIG. 1, the erosion evaluation device 10 includes an input receiving unit 11, a control unit 12, and a storage unit 13. The input reception unit 11 receives information and instructions input using an input device such as a keyboard, a mouse, a touch panel, a button, etc. For example, the input reception unit 11 receives input of information necessary for erosion evaluation, instructions to execute erosion evaluation processing, etc. The input reception unit 11 records the received information in the storage unit 13, and outputs it to the control unit 12.

[0014] The control unit 12 controls the execution of the erosion evaluation of the relaxation structure 100. The control unit 12 has a jet analysis unit 121 and an erosion evaluation unit 122. The jet analysis unit 121 analyzes the behavior of the jet 200. For example, the analysis results of the SIMMER code (e.g., the amount of jet discharged and the temperature) can be used for the jet behavior analysis. The SIMMER code is a calculation code capable of evaluating a hypothetical core collapse event of a fast breeder reactor. The jet analysis unit 121 analyzes the temporal change in the temperature and heat transfer coefficient of the jet 200 applied to the mitigation structure 100 using the analysis results of the SIMMER code or the like.

[0015] The erosion evaluation unit 122 sets boundary conditions based on the temperature and heat transfer coefficient of the jet 200 calculated by the jet analysis unit 121, and solves a one-dimensional unsteady heat conduction equation for the relaxation structure 100 to analyze the temperature distribution in the relaxation structure 100. For example, the erosion evaluation unit 122 prepares a one-dimensional unsteady heat conduction equation exemplified by the following formula (1) for each of the layers 1 to n in FIG. 2, and analyzes the temperature change of the layer 1 with the temperature and heat transfer coefficient of the jet 200 as boundary conditions, while simultaneously solving the one-dimensional unsteady heat conduction equation for the layer 2 with the temperature of the layer 1 obtained by the heat conduction analysis of the layer 1 as the boundary condition to analyze the temperature change of the layer 2. Similarly, the erosion evaluation unit 122 simultaneously solves the one-dimensional unsteady heat conduction equation for the remaining layers 3 to n with the heat transferred from the layer one layer above as the boundary condition, and analyzes the temporal change of the temperature of each layer.

[0016]

number

[0017] Here, in the above formula (1), ρ(T) is the density of relaxation structure 100, T is the temperature, Cp(T) is the specific heat that depends on the temperature T, Q is the amount of heat generated inside relaxation structure 100, z is the position in the z direction, k(T) is the thermal conductivity that depends on the temperature T, and t is time. The temperature T at each time t is calculated by solving formula (1).

[0018] When solving the one-dimensional unsteady heat conduction equation for each layer, the erosion evaluation unit 122 performs the following processes (A) to (C).

[0019] (A) The jet analysis unit 121 analyzes the temperature and heat transfer coefficient of the jet 200 from moment to moment, which change with time. The erosion evaluation unit 122 receives the analysis results and evaluates the heat load from the jet 200 applied to the mitigation structure 100. For example, the erosion evaluation unit 122 calculates the temperature of the end (top surface) of the mitigation structure 100 based on the temperature and heat transfer coefficient of the jet 200 analyzed by the jet analysis unit 121, and provides this temperature as the boundary condition of equation (1) for layer 1. This makes it possible to improve the accuracy of the analysis compared to the conventional analysis in which the jet discharge flow rate and temperature are constant.

[0020] (B) In the one-dimensional unsteady heat conduction equation (equation (1)), Cp (specific heat) is obtained from an HT (enthalpy temperature) curve that takes into account the latent heat of fusion, so that the latent heat at the time of melting of the relaxation structure 100 is taken into account. Specifically, the specific heat Cp that changes depending on temperature is obtained from the temperature T at that time and the enthalpy H corresponding to the temperature T by Cp=δH / δT with reference to the HT curve 301 illustrated in FIG. 3A, and the obtained Cp is applied to Cp(T) in equation (1).

[0021] (C) When the temperature of each layer reaches its melting point, the thermal conductivity k(T) of the one-dimensional unsteady heat conduction equation (equation (1)) is increased to reflect in the equation that the heat input from the molten jet does not stagnate in the molten part of the relaxation structure 100 (for example, the layer where the temperature T has reached the melting point, i.e., the eroded layer) and the heat is transmitted to the next layer (the layer one level below). This allows the calculation system for analyzing the behavior of heat transmission from layer 1 to layer n in sequence to be substantially removed from the calculation system, and a system can be created in which heat is transmitted to the next layer without loss. Conventionally, in order to express that the heat of the molten part is transmitted to the next layer without stagnation, a separate process was performed to remove the molten part from the calculation system, and this process generated a processing load. In contrast, in this embodiment, the conductivity k(T) is made sufficiently large (for example, 10 8 ) and there is no need to perform a separate process to remove the molten part from the calculation system, and the molten part can be effectively removed from the calculation system automatically, thereby reducing the processing load. Specifically, k, which changes depending on temperature, is found from the kT curve 302 shown in FIG. 3B, and the found k is applied to k(T) in formula (1). As shown in FIG. 3B, the thermal conductivity k is calculated based on the melting point T melt It remains almost constant until it reaches T melt The erosion evaluation unit 122 is configured to detect when the temperature T of the layer of interest reaches the melting point T melt When this is reached, the value of k(T) in equation (1) is changed based on the kT curve 302.

[0022] The memory unit 13 stores various initial values ​​required for erosion evaluation, various physical property values ​​(e.g., Cp, k, etc.) calculated based on the HT curve 301 illustrated in FIG. 3A and the kT curve 302 illustrated in FIG. 3B, data under analysis (the graphs in FIGS. 3A and 3B are created using the data under analysis. The data under analysis includes the graphs in FIGS. 3A and 3B), analysis results, etc.

[0023] (operation) Next, the flow of the erosion evaluation in this embodiment will be described with reference to FIG. FIG. 4 is a flowchart showing an example of an erosion evaluation method according to the embodiment. First, an operator inputs various information required for erosion evaluation (e.g., how many layers the mitigation structure 100 is divided into to be modeled, analysis results using SIMMER code, etc.) to the erosion evaluation device 10 and instructs the start of erosion evaluation. The input reception unit 11 acquires the input information, records it in the memory unit 13, and instructs the control unit 12 to start erosion evaluation. The control unit 12 instructs the jet analysis unit 121 to execute a behavior analysis of the jet 200. The jet analysis unit 121 analyzes the time changes in the temperature, heat transfer coefficient, etc. of the jet 200 applied to the mitigation structure 100 during a predetermined evaluation period (step S1). When the analysis is completed, the jet analysis unit 121 records the analysis results, such as the temperature and heat transfer coefficient of the jet 200, in the memory unit 13.

[0024] Next, the control unit 12 instructs the erosion evaluation unit 122 to analyze the heat transfer in the relaxation structure 100. Based on a model M in which a predetermined range 102 of the relaxation structure 100 is divided into n layers, the erosion evaluation unit 122 solves a one-dimensional unsteady heat conduction equation for each layer to analyze the time-dependent change in temperature distribution in the relaxation structure 100 (step S2). The erosion evaluation unit 122 reads out the temperature and heat transfer coefficient of the jet 200 recorded in the memory unit 13, calculates the temperature of the end of the relaxation structure 100, and sets this as a boundary condition. The erosion evaluation unit 122 solves equation (1) to analyze the temperature change of the layer 1 during a predetermined evaluation period. At that time, the erosion evaluation unit 122 calculates δH / δT based on the HT curve 301 illustrated in FIG. 3A and stored in the memory unit 13, and sets this value to Cp(T) in equation (1). By setting Cp(T) based on the HT curve 301, the latent heat at the time of melting of the layer 1 is reflected in the analysis, and the analysis accuracy is improved. In addition, the erosion evaluation unit 122 acquires the thermal conductivity k according to the temperature T by referring to the kT curve 302 exemplified in FIG. 3B stored in the storage unit 13, and sets this value to k(T) in the formula (1). By setting k(T) in the formula (1) based on the kT curve 302, it is possible to automatically reflect in the calculation system that the heat input from the jet 200 is not retained in the melting part and is transferred to the next part. By solving the formula (1) for the layer 1, the temperature in the layer 1 for each time t is obtained. The erosion evaluation unit 122 records the temperature in the layer 1 for each time t in the storage unit 13. While analyzing the temperature change of the layer 1, the erosion evaluation unit 122 solves the formula (1) for the layer 2 using the temperature of the layer 1 obtained by the analysis as a boundary condition, and analyzes the time-series temperature change of the layer 2 in a predetermined evaluation period. In this case, the erosion evaluation unit 122 also sets Cp(T) in formula (1) based on the temperature T at every moment and the HT curve 301, and sets k(T) in formula (1) based on the temperature T and the kT curve 302. Similarly, for layers 3 to n, the erosion evaluation unit 122 solves formula (1) while setting values ​​according to the temperature T for Cp(T) and k(T) with the temperature of the layer one level above as a boundary condition, and simultaneously analyzes the temperature change of each layer in a predetermined evaluation period. The erosion evaluation unit 122 records the analysis results of the temperature of each layer for each hour in the storage unit 13.

[0025] Next, the erosion evaluation unit 122 evaluates the erosion depth D (step S3). For example, if the analysis of temperature changes during a predetermined evaluation period shows that the temperatures of layers 1 and 2 are equal to or higher than the melting point, then, assuming that the thickness of each layer is z0, the erosion depth D is calculated as z0+z0=2×z0. Next, the control unit 12 outputs the results of the erosion evaluation (step S4). For example, the control unit 12 outputs the analysis results of the time series temperature distribution changes in the relaxation structure 100, the erosion depth D, etc. to a display device, an electronic file, etc.

[0026] (effect) As described above, according to this embodiment, the erosion of the structure (mitigation structure 100) and the transient behavior of the temperature distribution within the structure can be evaluated using the temperature of the end of the mitigation structure 100 calculated based on the analysis results in which the temperature of the jet 200, the heat transfer coefficient, etc. change over time as a boundary condition. This makes it possible to accurately evaluate the erosion of the structure by the jet 200.

[0027] In the above embodiment, an example has been described in which the erosion of the mitigation structure 100 installed inside a fast reactor is evaluated and the temperature distribution change is analyzed. However, the present embodiment may be applied to the evaluation and analysis of the erosion of structures inside and outside the reactor and the temperature distribution change inside the structures caused by molten core material released during a severe accident in a nuclear reactor such as a PWR (Pressurized Water Reactor) or a BWR (Boiling Water Reactor).

[0028] FIG. 5 is a diagram illustrating an example of a hardware configuration of the erosion evaluation device. The computer 900 includes a CPU 901, a main storage device 902, an auxiliary storage device 903, an input / output interface 904, and a communication interface 905. The above-mentioned erosion evaluation device 10 is implemented in the computer 900. The above-mentioned functions are stored in the auxiliary storage device 903 in the form of a program. The CPU 901 reads the program from the auxiliary storage device 903, develops it in the main storage device 902, and executes the above-mentioned processing according to the program. The CPU 901 also secures a storage area in the main storage device 902 according to the program. The CPU 901 also secures a storage area in the auxiliary storage device 903 for storing data being processed according to the program. The erosion evaluation device 10 may be configured by a plurality of computers 900.

[0029] A program for realizing all or part of the functions of the erosion evaluation device 10 may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into a computer system and executed to perform processing by each functional unit. The term "computer system" as used herein includes hardware such as an OS and peripheral devices. In addition, if a WWW system is used, the term "computer system" also includes a homepage providing environment (or display environment). In addition, the term "computer-readable recording medium" refers to a portable medium such as a CD, DVD, or USB, or a storage device such as a hard disk built into a computer system. In addition, when the program is distributed to a computer 900 via a communication line, the computer 900 that receives the program may deploy the program in the main storage device 902 and execute the above processing. In addition, the above program may be for realizing part of the above-mentioned functions, and may further be capable of realizing the above-mentioned functions in combination with a program already recorded in the computer system.

[0030] As described above, several embodiments according to the present disclosure have been described, but all of these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and gist of the invention.

[0031] <Additional Notes> The erosion evaluation method, the erosion evaluation device, and the program described in the embodiments can be understood, for example, as follows.

[0032] (1) The erosion evaluation method according to the first aspect includes the steps of: analyzing the changes over time in temperature and heat transfer coefficient of molten core material (jet 200); solving a one-dimensional unsteady heat conduction equation (equation (1)) showing the conduction of heat in a structure (mitigation structure 100) to which the heat from the released core material is transferred, using the temperature of the end of the structure based on the temperature and the heat transfer coefficient as boundary conditions, to analyze the changes over time in temperature distribution within the structure; and evaluating the erosion (erosion depth D) of the structure based on the results of the analysis of the temperature distribution. In the step of analyzing the changes over time in temperature distribution within the structure, a specific heat value calculated based on the correspondence between enthalpy and temperature taking into account the latent heat at the time of melting of the structure is set as the specific heat of the one-dimensional unsteady heat conduction equation, and a sufficiently large predetermined value indicating that the heat from the core material does not remain in the molten part of the structure is set as the thermal conductivity of the one-dimensional unsteady heat conduction equation. This allows for accurate evaluation of the erosion of the structure by the jet.

[0033] (2) A second aspect of the erosion evaluation method is the erosion evaluation method of (1), wherein in the step of analyzing the change over time in temperature distribution within the structure, the thermal conductivity of the structure is set according to the temperature until the temperature of the structure reaches its melting point, and when the temperature of the structure reaches its melting point, the sufficiently large predetermined value is set. This allows the analysis to automatically reflect the fact that heat input from the core material does not remain in the molten part but is transferred to the surrounding area.

[0034] (3) An erosion evaluation method according to a third aspect is the erosion evaluation method of (1) to (2), wherein in the step of analyzing the change over time in temperature distribution within the structure, the structure is divided into a plurality of layers, and for the topmost layer, the one-dimensional unsteady heat conduction equation is solved with the temperature and the temperature of the end of the structure based on the heat transfer coefficient as boundary conditions, and for the layers below the second layer, the one-dimensional unsteady heat conduction equation is solved with the temperature obtained as a result of analyzing the temperature distribution of the layer one level above as boundary conditions, and the change over time in temperature distribution within each of the layers is analyzed. By performing analysis by layer, it is possible to perform a more accurate evaluation. For example, compared to a method of calculating the relaxation structure as a single layer, by dividing it into multiple layers and calculating the time change in temperature distribution for each layer, it is possible to more accurately evaluate the temperature distribution inside the structure.

[0035] (4) A fourth aspect of the erosion evaluation method is an erosion evaluation method according to any one of (1) to (3), in which in the step of evaluating the erosion, a portion within the structure where the temperature has reached the melting point is regarded as erosion based on the temperature distribution within the structure, and the erosion depth is calculated. This makes it possible to evaluate the erosion depth of the structure.

[0036] (5) The erosion evaluation device of the fifth aspect includes a means for analyzing the temporal changes in temperature and heat transfer coefficient of molten core material, a means for analyzing the temporal changes in temperature distribution within the structure by solving a one-dimensional unsteady heat conduction equation showing the conduction of heat in a structure to which the heat from the released core material is transferred, with the temperature of the end of the structure based on the temperature and the heat transfer coefficient as boundary conditions, and a means for evaluating the erosion of the structure based on the results of the analysis of the temperature distribution, wherein the means for analyzing the temporal changes in temperature distribution within the structure sets the specific heat value of the one-dimensional unsteady heat conduction equation to a corresponding relationship between enthalpy and temperature taking into account the latent heat at the time of melting of the structure, and sets a sufficiently large predetermined value indicating that the heat from the core material will not remain in the molten part of the structure to the thermal conductivity of the one-dimensional unsteady heat conduction equation.

[0037] (6) A program according to a sixth aspect causes a computer to execute the steps of: analyzing changes over time in temperature and heat transfer coefficient of molten core material; analyzing changes over time in temperature distribution in the structure by solving a one-dimensional unsteady heat conduction equation that indicates the conduction of heat in a structure to which the heat from the released core material is transferred, using the temperature and the temperature of the end of the structure based on the heat transfer coefficient as boundary conditions; and evaluating erosion of the structure based on the results of the analysis of the temperature distribution. In the step of analyzing changes over time in temperature distribution in the structure, the computer executes the steps of: setting a specific heat value calculated based on a correspondence between enthalpy and temperature taking into account the latent heat at the time of melting of the structure to the specific heat of the one-dimensional unsteady heat conduction equation; and setting a sufficiently large predetermined value that indicates that the heat from the core material will not remain in the molten part of the structure to the thermal conductivity of the one-dimensional unsteady heat conduction equation. [Explanation of symbols]

[0038] 10. Erosion evaluation device 11 Input reception section 12. Control section 121 Jet Analysis Section 122 Erosion assessment section 13...Storage section 900...Computer 901···CPU 902...Main memory 903...Auxiliary storage device 904 Input / Output Interface 905 Communication Interface

Claims

1. Analyzing the time variation of temperature and heat transfer coefficient of core material discharged from the molten core; a step of analyzing a time-dependent change in temperature distribution in the structure by solving a one-dimensional unsteady heat conduction equation that shows the conduction of the heat in the structure to which the heat from the released core material is transferred, using the temperature and the temperature of the end of the structure based on the heat transfer coefficient as boundary conditions; evaluating the erosion of the structure based on the results of the temperature distribution analysis; having In the step of analyzing a change in temperature distribution over time within the structure, A value of specific heat calculated based on a correspondence relationship between enthalpy and temperature taking into account latent heat at the time of melting of the structure is set as the specific heat of the one-dimensional unsteady heat conduction equation; a thermal conductivity of the one-dimensional unsteady heat conduction equation is set to a predetermined value that is sufficiently large to indicate that the heat from the core material does not remain in a molten portion of the structure; Erosion assessment methods.

2. In the step of analyzing the change over time in temperature distribution in the structure, a thermal conductivity of the structure is set according to the temperature until the temperature of the structure reaches a melting point, and when the temperature of the structure reaches the melting point, the sufficiently large predetermined value is set. The erosion evaluation method according to claim 1 .

3. In the step of analyzing the change over time in temperature distribution within the structure, the structure is divided into a plurality of layers, and for the topmost layer, the one-dimensional unsteady heat conduction equation is solved with the temperature and the temperature of the end of the structure based on the heat transfer coefficient as boundary conditions, and for the layers below the second layer, the one-dimensional unsteady heat conduction equation is solved with the temperature obtained as a result of the analysis of the temperature distribution of the layer one level above as boundary conditions, thereby analyzing the change over time in temperature distribution within each of the layers. The erosion evaluation method according to claim 1 or 2.

4. In the step of evaluating the erosion, a portion in the structure where the temperature has reached a melting point is regarded as erosion based on a temperature distribution in the structure, and a erosion depth is calculated. The erosion evaluation method according to claim 1 or 2.

5. A means for analyzing the time variation of the temperature and heat transfer coefficient of the core material discharged from the molten core; a means for analyzing a change in temperature distribution over time within the structure by solving a one-dimensional unsteady heat conduction equation that represents the conduction of heat in a structure to which the heat from the released core material is transferred, using the temperature and the temperature of an end of the structure based on the heat transfer coefficient as boundary conditions; a means for evaluating erosion of the structure based on the results of the analysis of the temperature distribution; having The means for analyzing a change in temperature distribution over time within the structure includes: A value of specific heat calculated based on a correspondence relationship between enthalpy and temperature taking into account latent heat at the time of melting of the structure is set as the specific heat of the one-dimensional unsteady heat conduction equation; a thermal conductivity of the one-dimensional unsteady heat conduction equation is set to a predetermined value that is sufficiently large to indicate that the heat from the core material does not remain in a molten portion of the structure; Erosion assessment device.

6. On the computer, Analyzing the time variation of temperature and heat transfer coefficient of core material discharged from the molten core; a step of analyzing a time-dependent change in temperature distribution in the structure by solving a one-dimensional unsteady heat conduction equation that shows the conduction of the heat in the structure to which the heat from the released core material is transferred, using the temperature and the temperature of the end of the structure based on the heat transfer coefficient as boundary conditions; evaluating the erosion of the structure based on the results of the temperature distribution analysis; having In the step of analyzing a change in temperature distribution over time within the structure, A value of specific heat calculated based on a correspondence relationship between enthalpy and temperature taking into account latent heat at the time of melting of the structure is set as the specific heat of the one-dimensional unsteady heat conduction equation; A process of setting a sufficiently large predetermined value indicating that the heat from the core material does not remain in a molten portion of the structure as a thermal conductivity of the one-dimensional unsteady heat conduction equation; A program that executes the following.

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