Assessment method, assessment device, and program

Abstract

To provide a novel performance assessment method that is applicable in the event of a LOCA.SOLUTION: A method of assessing reactor core coolability in the event of a LOCA by using a test device that simulates a state where fuel pellets are ejected and scattered from fuel rods has the steps of: acquiring a test heat transfer model obtained from experiments carried out by using the test device; and comparing a basic heat transfer model with the test heat transfer model to correct the basic heat transfer model through at least one of variable corrections, variable additions, and adjustment coefficient corrections.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] There are known techniques for evaluating the cooling function as a characteristic of a nuclear reactor. For example, Patent Document 1 describes a method for evaluating the coolability of a nuclear reactor when scattered pellets are present, by conducting tests to confirm the manner in which fuel pellet fragments are scattered from fuel rods and the amount of scattered pellets that may occur in the event of a loss of coolant accident (LOCA) in the nuclear reactor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2024-23100 Summary of the Invention [Problem to be solved by the invention]

[0004] The test method described in Patent Document 1 can evaluate the state of pellet fragment scattering from fuel rods. In the event of a LOCA, reactor performance evaluation is required from various perspectives in addition to the state of pellet fragment scattering.

[0005] The present disclosure is intended to solve the above-mentioned problems, and aims to provide an evaluation method, evaluation device, and program that can provide a new performance evaluation technique in the event of a LOCA. [Means for solving the problem]

[0006] The evaluation method disclosed herein is a method for evaluating the coolability of a reactor core in the event of a LOCA using a test device that simulates the state in which fuel pellets are released and scattered from fuel rods, and includes the steps of: obtaining a test heat transfer model obtained from an experiment using the test device; and comparing a basic heat transfer model with the test heat transfer model, and correcting the basic heat transfer model by at least one of modifying variables, adding variables, and modifying an adjustment coefficient.

[0007] The evaluation device according to the present disclosure is an evaluation device having a calculation unit that evaluates the coolability of the core when a LOCA occurs using a test device that simulates the state in which fuel pellets are released and scattered from fuel rods, and the calculation unit executes the steps of: acquiring a test heat transfer model obtained from an experiment using the test device; and comparing a basic heat transfer model with the test heat transfer model, and correcting the basic heat transfer model by at least one of modifying variables, adding variables, and modifying an adjustment coefficient.

[0008] The program disclosed herein is a program for evaluating the coolability of a reactor core in the event of a LOCA using a test device that simulates the state in which fuel pellets are released and scattered from fuel rods, and causes a computer to execute the following steps: obtaining a test heat transfer model obtained from experiments using the test device; and comparing a basic heat transfer model with the test heat transfer model and correcting the basic heat transfer model by at least one of modifying variables, adding variables, and modifying adjustment coefficients. [Effects of the Invention]

[0009] According to the present disclosure, a new performance evaluation method can be provided in the event of a LOCA. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a block diagram schematically illustrating an evaluation device according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the general configuration of the test device. [Figure 3]FIG. 3 is a flowchart illustrating the flow of the evaluation method according to this embodiment. [Figure 4] FIG. 4 is a flowchart showing the process of obtaining the test heat transfer model. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Note that the present disclosure is not limited to these embodiments, and when there are multiple embodiments, the present disclosure also includes configurations in which the respective embodiments are combined.

[0012] FIG. 1 is a block diagram illustrating an evaluation device according to this embodiment. The evaluation device 1 evaluates the coolability of a reactor core in the event of a LOCA, which is a type of reactor safety verification. Specifically, in the event of a LOCA in a reactor (core) containing fuel irradiated to a high burnup, there is a possibility that fragmented pellets will be released from the high-burnup fuel. The evaluation device 1 evaluates the coolability of a reactor core in the event of a LOCA, particularly when fragmented pellets are deposited on components of a fuel assembly, which are a heat source, among other cooling evaluation methods for confirming that the coolability of a reactor is maintained. The evaluation device 1 evaluates the coolability of a reactor core in the event of a LOCA using a test device 2 that simulates the release and scattering of fuel pellets from a fuel rod. The test device 2 performs a test simulating the deposition of fragmented pellets on components of a fuel assembly, which are a heat source. Based on the test results obtained by the test device 2, the evaluation device 1 constructs a heat transfer model to be used in the evaluation of coolability when fragmented pellets are deposited.

[0013] (Configuration of evaluation device) As shown in FIG. 1, the evaluation device 1 includes a calculation unit 11, a storage unit 12, a display unit 13, and an input unit .

[0014] The calculation unit 11 includes an integrated circuit such as a CPU (Central Processing Unit). The calculation unit 11 executes processing such as evaluating the coolability of the core in the event of a LOCA based on input information. The storage unit 12 is any storage device such as a semiconductor storage device or a magnetic storage device. The storage unit 12 stores a program 15 for evaluating the coolability of the core in the event of a LOCA using the test apparatus 2 according to this embodiment. The program 15 causes a computer (the calculation unit 11) to execute processing for evaluating the coolability of the core in the event of a LOCA. The storage unit 12 stores various data used in the processing for evaluating the coolability of the core. The various data include, for example, information such as the specifications of the test apparatus 2, the specifications of the sample to be placed in the test apparatus 2, the specifications of the pellets, and information on a heat transfer model to be applied to the coolability evaluation. The information on the heat transfer model applied to the cooling performance evaluation includes information on a basic heat transfer model 16 stored in advance in the storage unit 12, information on a test heat transfer model 17 created based on test results using the test device 2, and information on a corrected heat transfer model 18 obtained by correcting the basic heat transfer model 16 based on the test heat transfer model 17. The display unit 13 is, for example, a display device such as a liquid crystal display. The input unit 14 is, for example, an input device such as a keyboard and a mouse. The display unit 13 and the input unit 14 may be integrated into an input display device that allows input operations, such as a touch panel.

[0015] (Test equipment configuration) 2 is a schematic diagram showing the general configuration of a test apparatus. The test apparatus 2 is a test apparatus that simulates the state of a fuel assembly when a LOCA occurs in a nuclear reactor. Specifically, the test apparatus 2 of this embodiment simulates a state in which, when a LOCA occurs, a phenomenon occurs in which atomized pellets are released and scattered from fuel rods in high burnup fuel (FFRD: Fuel Fragmentation, Relocation and Dispersal), and the atomized pellets released outside the fuel rods are deposited on components of the fuel assembly.

[0016] The test apparatus 2 holds a sample 3 that simulates a fuel assembly. Here, the fuel assembly has a grid structure in which a plurality of fuel rods are arranged in a square cross section of N×M cells (N and M are natural numbers) by a support grid. The fuel rod has a fuel cladding tube and granular pellets housed inside the fuel cladding tube. The sample 3 of the embodiment includes a simulated fuel rod 31 that simulates a fuel rod and a support grid 32 that supports the simulated fuel rod 31. The number of cells in the sample 3 is not particularly limited, but in one example, the sample 3 includes nine 3×3 cells. In other words, the sample 3 is a simulated grid in which a total of nine simulated fuel rods 31 are held by the 3×3 support grid 32.

[0017] The test device 2 includes a casing 21, a heat insulating material 22, a heat source (a lower heat source 23 and an upper heat source 24), a container 25 containing simulated pellet pieces 25A, and a temperature measuring means 26. The test device 2 is controlled by a control device 27.

[0018] The casing 21 accommodates the sample 3. The casing 21 surrounds the sample 3. The casing 21 has a hollow tubular structure extending vertically. The opening at the lower end of the casing 21 is sealed. The casing 21 has an inlet 21A to which a vapor inlet line 41 is connected. The inlet 21A is located at the bottom of the casing 21. The casing 21 holds a container 25. The container 25 is inserted into the opening at the upper end of the casing 21 to close the opening at the upper end. The casing 21 has an outlet 21B to which a vapor outlet line 42 is connected. The outlet 21B is located between the upper and lower ends of the casing 21. The outlet 21B is located at a position above the sample 3 inside the casing 21. The outlet 21B is located at a position below the container 25 inside the casing 21.

[0019] The heat insulating material 22 is provided on the outer periphery of the casing 21. The heat insulating material 22 surrounds the outer periphery of the casing 21. By providing the heat insulating material 22, it is possible to appropriately control the temperature around the sample 3. Furthermore, by reducing heat radiation, it is possible to reduce the energy used for heating.

[0020] The lower heating source 23 is provided on the outer periphery of the casing 21. The lower heating source 23 is provided at the bottom of the casing 21. The lower heating source 23 heats the lower region inside the casing 21. The lower heating source 23 heats the steam introduced into the bottom of the casing 21 from the steam introduction line 41. The lower heating source 23 is an electric furnace that generates heat electrically.

[0021] The upper heating source 24 is provided on the outer periphery of the casing 21. The upper heating source 24 is provided at the top of the casing 21. The upper heating source 24 heats the top of the casing 21. The upper heating source 24 is provided around the container 25. The upper heating source 24 heats the container 25, which is located in the upper region inside the casing 21. The heating of the container 25 heats the simulated pellet pieces 25A inside the container 25. The upper heating source 24 is an electric furnace that generates heat electrically.

[0022] Although the lower heating source 23 and the upper heating source 24 are electric heaters heated by electricity, the type of the heating source is not limited. The heating source may be structured so that a heating fluid is supplied to the inside, or may be structured so that the temperature is increased by burning fuel.

[0023] The container 25 is a hollow cylindrical member that contains simulated pellet fragments 25A. The container 25 is placed directly above the sample 3 placed inside the casing 21. The container 25 is open at both the top and bottom ends. An opening / closing mechanism 25B is provided in the container 25. The opening / closing mechanism 25B opens and closes the bottom opening of the container 25. The opening / closing mechanism 25B is controlled by the control device 27. The container 25 can store simulated pellet fragments 25A when the opening / closing mechanism 25B closes the bottom opening. When the opening / closing mechanism 25B opens the bottom opening of the container 25, the simulated pellet fragments 25A inside the container 25 fall from the bottom opening. The simulated pellet fragments 25A simulate the granular pellets contained inside the fuel cladding tube of a fuel rod. The simulated pellet fragments 25A fall from the container 25 onto the sample 3. The simulated pellet fragments 25A that fall onto the sample 3 are deposited on the surfaces of the simulated fuel rods 31 and support grids 32 of the sample 3. This simulates the situation in which pellet fragments scattered from the fuel rods are deposited on the fuel rod assembly when a LOCA occurs. Hereinafter, the area on the sample 3 where the simulated pellet fragments 25A are deposited will be referred to as the deposition area DA of the simulated pellet fragments 25A.

[0024] The temperature measuring means 26 measures the temperature of each part in the test device 2. The temperature measuring means 26 measures the inlet steam temperature T in and the outlet steam temperature T of the simulated pellet pile. out and the simulated pellet sediment temperature T p The temperature measuring means 26 measures the simulated pellet fragment deposit temperature T p The cladding temperature T of the simulated fuel rod 31 at the same height as the measurement point c The temperature measurement means 26 includes a plurality of temperature sensors. The temperature sensors are, for example, thermocouples. The temperature sensors (temperature-sensing parts of the temperature sensors) may be disposed at positions where the test heat transfer model 17 can be calculated based on the test results.

[0025] Simulated pellet pile temperature T p and the inlet steam temperature T in and outlet steam temperature T out This allows us to understand the heat transfer behavior from the simulated pellet pieces 25A to the "coolant (steam)".in Measurement point and outlet steam temperature T out The measurement point is set as close to the deposit as possible. This reduces the influence of external disturbances such as heat radiation to the outside air. in The measurement point P1 is set, for example, at the bottom of the deposition area DA or near the bottom surface of the support grid 32. out The measurement point P2 is set, for example, above the deposition area DA or near the top of the sample 3.

[0026] Simulated pellet pile temperature T p The measurement point P3 is set so as to come into contact with the pile of simulated pellet pieces 25A. The simulated pellet piece pile temperature T p is measured by, for example, adhering a simulated pellet piece 25A to the tip of a thermocouple (the temperature-sensing part of the temperature sensor). When a thermocouple is inserted into a deposit to measure the temperature, there is a possibility that voids exist within the deposit made up of multiple simulated pellet pieces 25A, and the temperature of the voids may be measured. According to the above method, it is possible to avoid measuring the temperature of the voids, and therefore the simulated pellet piece deposit temperature T p can be measured with high accuracy.

[0027] Cladding tube temperature T of simulated fuel rod 31 c The measurement point P4 is the simulated pellet pile temperature T p The measurement point P3 is set on the surface of the cladding of the simulated fuel rod 31 at the same height as the measurement point P3. This allows the heat transfer behavior from the simulated pellet pieces 25A to the fuel cladding to be confirmed with high accuracy.

[0028] Furthermore, temperature measuring means 26 measures the temperature of container 25. Measurement point P5 of the temperature of container 25 is, for example, the inner or outer circumferential surface of the portion of container 25 where simulated pellet pieces 25A are stored.

[0029] The control device 27 controls the lower heating source 23 and the upper heating source 24. The control device 27 controls the supply and stop of steam from a steam supply source (not shown) to the testing device 2 via a steam inlet line 41. The control device 27 controls the discharge and stop of steam from the casing 21 of the testing device 2 to a steam outlet line 42. The control device 27 controls temperature measurement by the temperature measurement means 26. The control device 27 controls the opening and closing operation of the container 25 by the opening and closing mechanism 25B. The control device 27 outputs the temperature measurement results to the evaluation device 1. The control device 27 includes at least one of an arithmetic circuit such as a CPU, a memory for storing various information such as calculation contents and programs, for example, a main storage device such as a RAM (Random Access Memory) and a ROM (Read Only Memory), and an external storage device such as an HDD (Hard Disk Drive).

[0030] The evaluation device 1 acquires the test results from the test device 2 via the control device 27. The evaluation device 1 acquires at least the temperature measurement results from the temperature measurement means 26 as the test results from the test device 2. The evaluation device 1 obtains a test heat transfer model 17 from the temperature measurement results.

[0031] (Evaluation method) FIG. 3 is a flowchart illustrating the flow of the evaluation method according to this embodiment. FIG. 4 is a flowchart showing the process of acquiring a test heat transfer model. The processes shown in FIGS. 3 and 4 are executed by the work of an operator, the control of the control device 27, and the process by the evaluation device 1. The evaluation method according to this embodiment is a method of evaluating the coolability of the core when FFRD occurs during a LOCA using the test device 2. One aspect of the evaluation method according to this embodiment is implemented by the calculation unit 11 of the evaluation device 1 executing the program 15. That is, the evaluation device 1 executes the evaluation method shown in FIG. 3 by processing the program 15 stored in the memory unit 12 with the calculation unit 11.

[0032] In the evaluation method according to the embodiment, a known heat transfer model (heat transfer equation) can be used as the basic heat transfer model 16. Generally, there is a discrepancy between the theoretical solution based on the heat transfer equation and the test results. Therefore, in the embodiment, the discrepancy between the theoretical solution and the test results is reduced by creating a corrected heat transfer model 18 by modifying or adding variables constituting the basic heat transfer model 16 or by adding an adjustment coefficient.

[0033] Specifically, in the evaluation method according to this embodiment, a test heat transfer model 17 is obtained based on the test results obtained by the test device 2, and the basic heat transfer model 16 is modified by comparing the obtained test heat transfer model 17 with the basic heat transfer model 16. The basic heat transfer model 16 and the test heat transfer model 17 according to this embodiment assume heat transfer behavior in a situation where pellets released to the outside of a fuel rod are deposited on a component of a fuel assembly, and include a heat transfer model between the deposited "pellet fragments" and the "coolant (steam)" and a heat transfer model between the deposited "pellet fragments" and the "cladding tube."

[0034] 3, the calculation unit 11 of the evaluation device 1 acquires a test heat transfer model 17 obtained from an experiment using the test device 2 (step S10). The calculation unit 11 creates a test heat transfer model 17 for the test device 2 based on the results of the experiment using the test device 2. The test heat transfer model 17 is a heat transfer model that represents heat transfer when pellet fragments scattered from fuel rods upon the occurrence of a LOCA are deposited on a fuel rod assembly.

[0035] In step S10 of acquiring the test heat transfer model 17, as shown in FIG. 4, the control device 27 supplies steam to the test device 2 containing the sample 3 including the simulated fuel rod 31, and maintains it at a predetermined temperature (step S20).

[0036] The control device 27 starts supplying steam from a steam supply source (not shown) to the steam inlet line 41. The steam is introduced from the steam inlet line 41 into the lower part of the casing 21 of the test device 2. The control device 27 controls the lower heat source 23 so as to heat the steam introduced into the lower part of the casing 21. The control device 27 acquires the temperature measurement result by the temperature measurement means 26 and calculates the steam temperature (inlet steam temperature T in and outlet steam temperature T out The lower heat source 23 is controlled so that the lower heat source 23 is maintained at a predetermined temperature that is assumed to occur when a LOCA occurs. The predetermined temperature that is assumed to occur when a LOCA occurs is not particularly limited, but is, for example, a predetermined temperature in the range of 600°C to 700°C.

[0037] The control device 27 maintains the container 25 enclosing the simulated pellet pieces 25A at a temperature higher than the steam temperature inside the testing device 2 (step S22). The control device 27 controls the upper heat source 24 to heat the container 25 arranged at the top of the casing 21. The control device 27 acquires the temperature measurement results from the temperature measurement means 26 and controls the upper heat source 24 to maintain the container temperature at a predetermined temperature higher than the steam temperature. As a result, the simulated pellet pieces 25A stored inside the container 25 are also maintained at a predetermined temperature higher than the steam temperature. The predetermined temperature higher than the steam temperature is not particularly limited, but is, for example, 900°C.

[0038] The control device 27 drops the simulated pellet pieces 25A from the container 25 onto the simulated fuel rod 31 (step S24). The control device 27 controls the opening / closing mechanism 25B to open the bottom opening of the container 25. When the opening / closing mechanism 25B opens the bottom opening of the container 25, the heated simulated pellet pieces 25A stored inside the container 25 drop from the container 25. The dropped simulated pellet pieces 25A are deposited on the surfaces of the simulated fuel rod 31 and support grid 32 of the sample 3 in the deposition area DA.

[0039] The control device 27 measures the temperature in the deposition area DA of the simulated pellet pieces 25A (step S26). The control device 27 acquires the temperature measurement result from the temperature measurement means 26. In step S26, the control device 27 acquires the inlet steam temperature T in and the outlet steam temperature T of the simulated pellet pile. out and the simulated pellet sediment temperature T p and the cladding temperature T of the simulated fuel rod 31. c and measure.

[0040] The control device 27 outputs the acquired temperature measurement results to the evaluation device 1. As a result, the evaluation device 1 calculates the inlet steam temperature T in and the outlet steam temperature T of the simulated pellet pile. out and the simulated pellet sediment temperature T p and the cladding temperature T of the simulated fuel rod 31. c and get.

[0041] The calculation unit 11 of the evaluation device 1 obtains a test heat transfer model 17 from the temperature measurement results (step S28). As described above, the test heat transfer model 17 includes a heat transfer model between the pellet pieces and the coolant (steam) in the test (hereinafter referred to as "test heat transfer model A") and a heat transfer model between the pellet pieces and the cladding tube in the test (hereinafter referred to as "test heat transfer model B"). The evaluation device 1 obtains the test heat transfer model A and the test heat transfer model B from the temperature measurement results.

[0042] (Test heat transfer model A between pellet pieces and coolant) The calculation unit 11 calculates the test heat transfer model A using the following formulas (1) and (2). The calculation unit 11 calculates the test heat transfer model A using the formulas (1) and (2). p-v Get.

[0043]

number

[0044] where m vis the steam mass flow rate (kg / s). C v is the specific heat of steam (J / kg / K). T out is the outlet steam temperature of the simulated pellet pile (°C). T in is the inlet steam temperature of the simulated pellet pile (°C). T p is the temperature of the simulated pellet pile (°C). T v,p is the steam temperature inside the simulated pellet pile (°C). p is the pellet surface area (m 2 ) Steam mass flow rate m v is the inlet boundary condition of test device 2. Steam specific heat C v is the physical property of steam. Pellet surface area S p is calculated from the typical dimensions of the simulated pellet pieces 25A. Therefore, the steam mass flow rate m v , steam specific heat C v , pellet surface area S p is a known constant, and is set from the input unit 14, for example.

[0045] Inlet steam temperature T in and outlet steam temperature T out and the simulated pellet sediment temperature T p is a measurement value obtained from the temperature measuring means 26. The vapor temperature T v,p is the inlet steam temperature T in and outlet steam temperature T out The steam temperature T v,p may be directly measured by the temperature measuring means 26. However, even if the tip of a thermocouple is inserted into the void in the deposit, it is difficult to measure accurately due to the influence of particles around the void. v,p It is preferable to assume the average value of the inlet and outlet steam temperatures.

[0046] (Test heat transfer model B between pellet fragments and cladding tube) The calculation unit 11 calculates the test heat transfer model B using the following formulas (3) and (4). The calculation unit 11 calculates the heat transfer coefficient h p-c Get.

[0047]

number

[0048] where M c is the mass of the cladding tube (kg). C c is the specific heat of the cladding (J / kg / K). ΔT c is the change in cladding temperature over time (℃). T p is the simulated pellet pile temperature. T c is the cladding temperature. S c is the contact area between the pellet fragments and the cladding tube (m 2 ) The mass of the cladding tube M c , specific heat of cladding tube C c is a physical property value. Contact area S c is calculated from the size of the simulated pellet fragment. Therefore, the mass M c , specific heat C c , contact area S c is a known constant, and is set from the input unit 14, for example.

[0049] Cladding tube temperature T c is a measurement value obtained from the temperature measurement means 26. The change in cladding temperature over time ΔT c For the cladding temperature T c The controller 27 acquires temperature measurements at a sampling time shorter than the cladding temperature time constant. Preferably, the cladding temperature T c is measured at multiple points along the vertical direction of the simulated fuel rod 31. c You can check whether the measurement is accurate.

[0050] As a result, the calculation unit 11 of the evaluation device 1 calculates a test heat transfer model A (heat transfer coefficient h) between the pellet pieces and the coolant (steam) in the test as a test heat transfer model 17 from the temperature measurement results. p-v ), and the test heat transfer model B between the pellet fragments and the cladding (heat transfer coefficient h p-c ) to get the

[0051] 3, the calculation unit 11 of the evaluation device 1 compares the basic heat transfer model 16 with the test heat transfer model 17, and corrects the basic heat transfer model 16 by at least one of modifying a variable, adding a variable, and modifying an adjustment coefficient (step S12). In the embodiment, the calculation unit 11 corrects the basic heat transfer model 16 by modifying the adjustment coefficient.

[0052] As described above, the basic heat transfer model 16 includes a heat transfer model between pellet pieces and coolant (steam) (hereinafter referred to as "basic heat transfer model A") and a heat transfer model between pellet pieces and cladding tubes (hereinafter referred to as "basic heat transfer model B").

[0053] (Basic heat transfer model A between pellet pieces and coolant (steam)) The Inaba-Fukuda equation shown in equation (5) is exemplified as the basic heat transfer model A. The Inaba-Fukuda equation is shown in the following document: Inaba, Fukuda, "Unsteady Heat Dissipation Characteristics of a Horizontal Cylindrical Heat Storage Tank Packed with Spherical Particles", Transactions of the Japan Society of Mechanical Engineers (Part B), Vol. 51, No. 470, pp. 3183-3190, 1985 The Inaba-Fukuda equation applies to the heat transfer between the pellet fragments and the coolant (steam) inside a circular pipe.

[0054]

number

[0055] N u is the Nusselt number. P r is the Prandtl number. R e is the Reynolds number. D p is the particle size of the pellet fragments. D is the flow channel diameter. λ v is the thermal conductivity of steam. α, β, γ, and δ are adjustment coefficients.

[0056] In this way, basic heat transfer model 16 (basic heat transfer model A) includes adjustment coefficients α, β, γ, and δ. Adjustment coefficient α is an adjustment coefficient that adjusts the entire heat transfer model. Adjustment coefficient β is an adjustment coefficient related to the influence of the ambient temperature inside the core. Adjustment coefficient γ is an adjustment coefficient related to the influence of the fluid flow inside the core. Adjustment coefficient δ is an adjustment coefficient related to the influence of the flow path shape inside the core. In the Inaba-Fukuda equation, which assumes a circular tubular structure, α = 0.633, β = 0.333, γ = 0.658, and δ = 0.761 are used.

[0057] In the embodiment, the calculation unit 11 compares the basic heat transfer model 16 with the test heat transfer model 17 and corrects the basic heat transfer model 16 by modifying the adjustment coefficients. The calculation unit 11 sets the values ​​of the adjustment coefficients α, β, γ, and δ used in the Inaba-Fukuda equation as initial values, and calculates the test heat transfer model 17 (heat transfer coefficient h) calculated from the results of multiple tests using the test device 2. p-v ) and correct at least one of the adjustment coefficients α, β, γ, and δ so that the basic heat transfer model 16 matches the experimental results.

[0058] The adjustment coefficient δ has a significant effect because the Inaba-Fukuda equation assumes a circular pipe flow path, which differs from the flow path shape of the test apparatus 2. The adjustment coefficient γ has a significant effect because differences in flow path shape also affect the flow of the fluid (steam). The adjustment coefficient β is also significant because the Prandtl number is determined by the ambient temperature, and differences in ambient temperature are absorbed to some extent by the Prandtl number itself. The adjustment coefficient α is used for final adjustment of the heat transfer model, and therefore its effect in reducing deviation from the test results is smaller than that of the other adjustment coefficients. The adjustment priority is highest for the adjustment coefficient δ, followed by the adjustment coefficient γ, the adjustment coefficient β, and finally the adjustment coefficient α. In this embodiment, it is preferable to adjust at least the adjustment coefficient δ among the adjustment coefficients α, β, γ, and δ.

[0059] In the embodiment, the calculation unit 11 calculates the test heat transfer model A (heat transfer coefficient h p-v), the four adjustment coefficients α, β, γ, and δ are adjusted so that the basic heat transfer model A matches the experimental results. By adjusting the values ​​of the four adjustment coefficients α, β, γ, and δ, the deviation between the theoretical solution and the test results can be effectively reduced.

[0060] (Basic heat transfer model B between "pellet fragments" and "cladding tube") As an example of basic heat transfer model B, equation (6) is shown.

number

[0061] h p-c is the heat transfer coefficient between the pellet fragments and the cladding tube. D p is the particle size of the pellet pieces. f is the thermal conductivity of steam. ew is the effective thermal conductivity near the wall. er is the effective thermal conductivity in the direction perpendicular to the flow (radial direction). α is an adjustment factor.

[0062] The adjustment coefficient α in equation (6) is an adjustment coefficient that adjusts the entire heat transfer model. In this embodiment, the calculation unit 11 compares the basic heat transfer model B with the test heat transfer model B, and corrects the basic heat transfer model B by modifying the adjustment coefficient. The calculation unit 11 uses the test heat transfer model B (heat transfer coefficient h p-c ) based on the above, the adjustment coefficient α is corrected so that the basic heat transfer model B matches the experimental results.

[0063] In step S12, the calculation unit 11 stores the correction equation obtained by correcting the adjustment coefficients α, β, γ, and δ of equation (5) and the correction equation obtained by correcting the adjustment coefficient α of equation (6) as the corrected heat transfer model 18 in the memory unit 12.

[0064] The calculation unit 11 evaluates the coolability of the core when a LOCA of the evaluation target occurs using the corrected heat transfer model 18 (the corrected basic heat transfer model 16) (step S14). The calculation unit 11 acquires information about the plant to be evaluated, i.e., the nuclear reactor, using the input unit 14. The calculation unit 11 evaluates the coolability when atomized pellets are deposited on components of a fuel assembly based on the information about the evaluation target and the corrected heat transfer model 18. This allows the coolability of the core to be evaluated when a LOCA-induced pellet release (FFRD) phenomenon occurs and atomized pellets are deposited in the fuel assembly.

[0065] (effect) An evaluation method according to a first aspect of the present disclosure is a method for evaluating the coolability of a core during a LOCA event using a test apparatus 2 that simulates the release and scattering of fuel pellets from fuel rods. The evaluation method includes the steps of: acquiring a test heat transfer model 17 obtained through an experiment using the test apparatus 2; and comparing the test heat transfer model 17 with a basic heat transfer model 16 and correcting the basic heat transfer model 16 by at least one of modifying variables, adding variables, and modifying an adjustment coefficient. According to the present disclosure, the basic heat transfer model 16 used in heat transfer analysis can be corrected using the test heat transfer model 17 obtained by simulating the state of the core during a LOCA event using the test apparatus 2. In other words, when a special situation, such as when a LOCA occurs in a nuclear reactor (core), is assumed, a theoretical solution based on the commonly used basic heat transfer model 16 diverges from the test results, and no appropriate evaluation method has been established. According to the present disclosure, a corrected heat transfer model that closely matches the state of the core during a LOCA event can be obtained, thereby providing a new performance evaluation method for the coolability of a core during a LOCA event.

[0066] An evaluation method according to a second aspect of the present disclosure is the evaluation method according to the first aspect, in which the test heat transfer model 17 includes at least one of a heat transfer model between pellet fragments and the coolant and a heat transfer model between pellet fragments and the cladding tube in the case where pellet fragments scattered from the fuel rods in the event of a LOCA are deposited on the fuel rod assembly. According to the present disclosure, by correcting the basic heat transfer model 16 using the obtained test heat transfer model 17, it is possible to realize an evaluation model for the coolability of the core in a situation where pellet fragments scattered from the fuel rods in the event of a LOCA are deposited on the fuel rod assembly, which is the heat source.

[0067] An evaluation method according to a third aspect of the present disclosure is the evaluation method according to the first or second aspect, wherein the step of obtaining the test heat transfer model 17 includes the steps of supplying steam to a test apparatus 2 containing a sample 3 including a simulated fuel rod 31 and maintaining the steam at a predetermined temperature, maintaining a container 25 enclosing simulated pellet pieces 25A at a temperature higher than the steam temperature in the test apparatus 2, dropping the simulated pellet pieces 25A from the container 25 onto the simulated fuel rod 31, measuring the temperature in the deposition area DA of the simulated pellet pieces 25A, and obtaining the test heat transfer model 17 from the temperature measurement results. According to the present disclosure, the test apparatus 2 can appropriately simulate the situation in which pellet pieces scattered from a fuel rod during a LOCA occur and deposit on a fuel rod assembly, thereby obtaining accurate temperature measurement results appropriate to the situation. As a result, a highly accurate test heat transfer model 17 reflecting the expected situation can be obtained.

[0068] The evaluation method according to a fourth aspect of the present disclosure is the evaluation method according to the third aspect, wherein the test heat transfer model 17 and the basic heat transfer model 16 include a heat transfer model between the pellet pieces and the coolant, and in the step of measuring the temperature in the deposition area DA of the simulated pellet pieces 25A, the inlet steam temperature T in and the outlet steam temperature T of the simulated pellet pile. out and the simulated pellet sediment temperature T pAccording to the present disclosure, a heat transfer model between the accumulated pellet fragments and the coolant can be obtained when pellet fragments scattered from fuel rods are deposited on a fuel rod assembly in the event of a LOCA. This makes it possible to evaluate the temperature status of the pellet fragments deposited on the fuel rod assembly.

[0069] An evaluation method according to a fifth aspect of the present disclosure is the evaluation method according to the third or fourth aspect, wherein the test heat transfer model 17 and the basic heat transfer model 16 include a heat transfer model between the pellet fragments and the cladding tube, and in the step of measuring the temperature in the deposition area DA of the simulated pellet fragments 25A, a simulated pellet fragment deposition temperature T p and the simulated pellet sediment temperature T p The cladding temperature T of the simulated fuel rod 31 at the same height as the measurement point c According to the present disclosure, a heat transfer model between pellet fragments and cladding tubes can be obtained when pellet fragments scattered from fuel rods are deposited on a fuel rod assembly during a LOCA. This makes it possible to evaluate the temperature status of the pellet fragments and cladding tubes deposited on the fuel rod assembly.

[0070] An evaluation method according to a sixth aspect of the present disclosure is the evaluation method according to any one of the first to fifth aspects, wherein the basic heat transfer model 16 includes an adjustment coefficient δ related to the influence of the flow path shape in the core, and the adjustment coefficient δ related to the influence of the flow path shape is corrected in the step of correcting the basic heat transfer model 16. According to the present disclosure, the basic heat transfer model 16 can be corrected using the test heat transfer model 17 to account for the influence of differences in flow path shape, which has a particularly large influence on the heat transfer model. Therefore, it is possible to effectively reduce the discrepancy between the theoretical solution using the corrected heat transfer model and the test results.

[0071] An evaluation method according to a seventh aspect of the present disclosure is the evaluation method according to any one of the first to sixth aspects, wherein the basic heat transfer model 16 includes an adjustment coefficient γ related to the influence of fluid flow in the core, and the adjustment coefficient γ related to the influence of flow is modified in the step of correcting the basic heat transfer model 16. According to the present disclosure, it is possible to reduce the discrepancy between the theoretical solution using the heat transfer model and the test results due to the influence of the fluid (coolant) flow in the core.

[0072] An evaluation method according to an eighth aspect of the present disclosure is the evaluation method according to any one of the first to seventh aspects, wherein the basic heat transfer model 16 includes an adjustment factor β related to the influence of the ambient temperature in the core, and the adjustment factor β related to the influence of the ambient temperature is modified in the step of correcting the basic heat transfer model 16. According to the present disclosure, it is possible to reduce the deviation between the theoretical solution using the heat transfer model and the test results due to the influence of the ambient temperature in the core.

[0073] An evaluation method according to a ninth aspect of the present disclosure is the evaluation method according to any one of the first to eighth aspects, wherein the basic heat transfer model 16 includes an adjustment coefficient α for adjusting the entire heat transfer model, and the adjustment coefficient α for adjusting the entire heat transfer model is modified in the step of correcting the basic heat transfer model 16. According to the present disclosure, the heat transfer model can be fine-tuned to reduce the influence of various deviation factors that cannot be derived from typical factors that cause a deviation between a theoretical solution using the heat transfer model and test results. This allows the theoretical solution using the heat transfer model to approach the test results.

[0074] An evaluation device according to a tenth aspect of the present disclosure includes a calculation unit 11 that evaluates the coolability of a core in the event of a LOCA using a test device 2 that simulates the release and scattering of fuel pellets from fuel rods. The calculation unit 11 executes the following steps: acquiring a test heat transfer model 17 obtained from an experiment using the test device 2; and comparing the test heat transfer model 17 with a basic heat transfer model 16 and correcting the basic heat transfer model 16 by at least one of modifying variables, adding variables, and modifying an adjustment coefficient. According to the present disclosure, the basic heat transfer model 16 used in heat transfer analysis can be corrected using the test heat transfer model 17 obtained by simulating the state of a core in the event of a LOCA using the test device 2. In other words, assuming a special situation such as a LOCA occurring in a nuclear reactor (core), a theoretical solution based on the commonly used basic heat transfer model 16 deviates from the test results, and therefore no appropriate evaluation method has been established. According to the present disclosure, it is possible to obtain a corrected heat transfer model that closely matches the state of the core when a LOCA occurs, thereby providing a new performance evaluation method for the coolability of the core when a LOCA occurs.

[0075] A program 15 according to an eleventh aspect of the present disclosure is a program 15 for evaluating the coolability of a core in the event of a LOCA using a test apparatus 2 that simulates the release and scattering of fuel pellets from fuel rods. The program 15 causes a computer to execute the following steps: acquiring a test heat transfer model 17 obtained from an experiment using the test apparatus 2; and comparing the test heat transfer model 17 with a basic heat transfer model 16 and correcting the basic heat transfer model 16 by at least one of modifying variables, adding variables, and modifying an adjustment coefficient. According to the present disclosure, the basic heat transfer model 16 used in heat transfer analysis can be corrected using the test heat transfer model 17 obtained by simulating the state of the core in the event of a LOCA using the test apparatus 2. In other words, assuming a special situation such as a LOCA occurring in a nuclear reactor (core), a theoretical solution based on the commonly used basic heat transfer model 16 diverges from the test results, and no appropriate evaluation method has been established. According to the present disclosure, a corrected heat transfer model that closely matches the state of the core in the event of a LOCA can be obtained, thereby providing a new performance evaluation method for the coolability of a core in the event of a LOCA.

[0076] Although the embodiments of the present disclosure have been described above, the embodiments are not limited to the contents of these embodiments. Furthermore, the above-described components include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the above-described components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the above-described embodiments.

[0077] For example, in the above embodiment, an example has been described in which the basic heat transfer model 16 is corrected by at least one of correcting the adjustment coefficient of the basic heat transfer model 16, but the basic heat transfer model 16 may also be corrected by correcting or adding a variable, or the basic heat transfer model 16 may be corrected by a combination of two or more of correcting the variable, adding a variable, and correcting the adjustment coefficient. Furthermore, in the above embodiment, an example has been described in which the test heat transfer model 17 includes a test heat transfer model A between the pellet pieces and the coolant and a test heat transfer model B between the pellet pieces and the cladding tube, but the test heat transfer model 17 may include only one of the test heat transfer model A and the test heat transfer model B. For example, the test heat transfer model A is compared with the basic heat transfer model A to obtain the corrected heat transfer model 18, and the basic heat transfer model A may be corrected to obtain the corrected heat transfer model, while a known heat transfer model may be used for the heat transfer model between the pellet pieces and the cladding tube without performing correction using the test heat transfer model. [Explanation of symbols]

[0078] 1 Evaluation device 2. Test equipment 3 Sample 11 Arithmetic section 15 Programs 16 Basic Heat Transfer Model 17 Test heat transfer model 25 Container 25A simulated pellet fragments 31 Simulated fuel rod α Adjustment coefficient (adjustment coefficient for adjusting the entire heat transfer model) β Adjustment factor (adjustment factor for the influence of ambient temperature) γ Adjustment coefficient (adjustment coefficient for the effect of fluid flow) δ Adjustment coefficient (adjustment coefficient for the effect of flow path shape)

Claims

1. A method for evaluating the coolability of a reactor core in the event of a LOCA using a test device that simulates the release and scattering of fuel pellets from a fuel rod, comprising: obtaining a test heat transfer model determined from experiments using the test apparatus; comparing a basic heat transfer model with the test heat transfer model and correcting the basic heat transfer model by at least one of modifying variables, adding variables, and modifying adjustment coefficients; Evaluation method.

2. the test heat transfer model includes at least one of a heat transfer model between the pellet fragments scattered from the fuel rods and the coolant and a heat transfer model between the pellet fragments and the cladding tube in the case where the pellet fragments scattered from the fuel rods upon the occurrence of a LOCA are deposited in the fuel rod assembly; The evaluation method according to claim 1 .

3. obtaining the test heat transfer model includes: supplying steam to the test apparatus containing a sample including a simulated fuel rod and maintaining the test apparatus at a predetermined temperature; maintaining a container containing simulated pellet pieces at a temperature higher than the steam temperature within the test apparatus; dropping the simulated pellet pieces from the container onto the simulated fuel rod; measuring the temperature in the deposition area of ​​the simulated pellet pieces; and determining the test heat transfer model from the temperature measurement results. The evaluation method according to claim 2.

4. the test heat transfer model and the basic heat transfer model include a heat transfer model between the pellet pieces and a coolant; In the step of measuring the temperature in the deposition region of the simulated pellet fragments, an inlet steam temperature of the simulated pellet fragment deposit, an outlet steam temperature of the simulated pellet fragment deposit, and a simulated pellet fragment deposit temperature are measured. The evaluation method according to claim 3.

5. the test heat transfer model and the basic heat transfer model include a heat transfer model between the pellet pieces and the cladding tube; In the step of measuring the temperature in the accumulation region of the simulated pellet fragments, the simulated pellet fragment accumulation temperature and the cladding temperature of the simulated fuel rod at the same height position as the measurement point of the simulated pellet fragment accumulation temperature are measured. The evaluation method according to claim 3.

6. the basic heat transfer model includes an adjustment coefficient for an effect of a flow path shape within the reactor core; In the step of correcting the basic heat transfer model, an adjustment coefficient relating to the influence of the flow path shape is corrected. The evaluation method according to any one of claims 1 to 5.

7. the basic heat transfer model includes an adjustment factor for the effect of fluid flow within the reactor core; In the step of correcting the basic heat transfer model, an adjustment coefficient relating to the influence of the flow is modified. The evaluation method according to any one of claims 1 to 5.

8. the basic heat transfer model includes an adjustment factor for the effect of ambient temperature within the reactor core; In the step of correcting the basic heat transfer model, an adjustment coefficient relating to the influence of the ambient temperature is corrected. The evaluation method according to any one of claims 1 to 5.

9. the basic heat transfer model includes an adjustment coefficient for adjusting the entire heat transfer model; In the step of correcting the basic heat transfer model, an adjustment coefficient for adjusting the entire model is modified. The evaluation method according to any one of claims 1 to 5.

10. An evaluation device having a calculation unit for evaluating the coolability of a reactor core when a LOCA occurs using a test device that simulates the state in which fuel pellets are released and scattered from a fuel rod, The calculation unit obtaining a test heat transfer model determined from experiments using the test apparatus; comparing a basic heat transfer model with the test heat transfer model and correcting the basic heat transfer model by modifying variables, adding variables, and / or modifying adjustment coefficients; Evaluation equipment.

11. A program for evaluating the coolability of a reactor core in the event of a LOCA using a test device that simulates the release and scattering of fuel pellets from fuel rods, obtaining a test heat transfer model determined from experiments using the test apparatus; comparing a basic heat transfer model with the test heat transfer model, and correcting the basic heat transfer model by at least one of modifying a variable, adding a variable, and modifying an adjustment coefficient; program.

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