A method and system for analyzing loss of coolant accident in solid fuel of pressurized water reactor

Abstract

The present invention discloses a method and system for analyzing a loss of coolant accident in solid fuel of a pressurized water reactor, comprising the following steps: determining the strength parameters of the cladding material in the pressurized water reactor fuel cladding, and establishing a failure judgment criterion for the cladding in the fuel pellet; determining the relationship between the coolant height and flow rate and time based on the LOCA case of the solid fuel, fitting the relationship into an empirical function, and establishing a coolant loss and reflooding model to realize the entire process of coolant loss, replenishment, and flooding the core over time; calculating the temperature distribution of the fuel pellet and the cladding and the stress and strain of the cladding at each moment based on the fuel pellet linear power and the physical properties of the fuel pellet, the cladding, and the gap between the fuel pellet and the cladding, and the coolant loss and reflooding model; and analyzing the cladding failure of the fuel pellet based on the stress and strain of the cladding in the fuel pellet and the failure judgment criterion of the cladding in the fuel pellet.

Description

Technical Field

[0001] The present invention relates to the field of nuclear reactor fuel rod thermal performance analysis, and in particular to an analysis method and system for a pressurized water reactor solid fuel coolant loss accident. Background Art

[0002] Since the advent of nuclear reactors, efforts have been ongoing to improve their safety. Studying fuel performance under accident conditions, such as loss of coolant accidents (LOCAs) and reactivity-induced accidents (RIAs), is of great significance. Currently, calculations of pressurized water reactor (PWR) fuel are primarily based on normal reactor operation. Few methods exist for analyzing fuel performance under LOCA (Loss of Coolant Accident) conditions. The international fuel performance analysis program FRAPCON utilizes a code integration approach, resulting in a long development cycle and considerable difficulty in mastering its application (CN201510830405.2). To analyze the safety of PWR solid fuel, a fast, reliable, and accurate method for analyzing LOCA conditions is necessary. The COMSOL finite element analysis platform enables rapid modeling and offers flexible input and output interfaces. This allows for rapid and accurate analysis of PWR solid fuel LOCA conditions using an efficient numerical solver. Summary of the Invention

[0003] To overcome the defects and shortcomings of the prior art, the first objective of the present invention is to provide an analysis method for loss of coolant accidents in solid fuel pressurized water reactors. This method uses a fully coupled heat transfer and solid mechanics calculation method, combined with a loss of coolant and reflooding module, to calculate the temperature distribution of the fuel pellets and cladding and the stress and strain of the cladding at each moment under LOCA conditions, while also taking into account cladding failure to obtain accurate and reliable calculation results.

[0004] A second object of the present invention is to provide a calculation system for a pressurized water reactor solid fuel coolant loss accident.

[0005] A third object of the present invention is to provide a storage medium.

[0006] A fourth object of the present invention is to provide a computing device.

[0007] The present invention is achieved through at least one of the following technical solutions.

[0008] A method for analyzing a loss of coolant accident in a solid fuel of a pressurized water reactor (PWR) is disclosed. A coolant channel exists outside the solid fuel rod of the PWR. When a loss of coolant accident occurs, the fuel rod cooling efficiency decreases and the temperature increases until the rod is refilled with coolant and cooling is restored. The method specifically comprises the following steps:

[0009] (1) Determining the strength parameters of the cladding material in the pressurized water reactor fuel rod and establishing a failure judgment criterion for the cladding in the fuel rod;

[0010] (2) Based on the solid fuel LOCA case, the relationship between coolant height and flow rate over time is determined and fitted into an empirical function to establish a coolant loss and reflooding model, realizing the entire process of coolant loss, replenishment, and reflooding over time;

[0011] (3) Based on the fuel pellet linear power and the physical properties of the fuel pellet, cladding, and the gap between the fuel pellet and the cladding, a coolant loss and reflooding model is used to calculate the temperature distribution of the fuel pellet and the cladding, as well as the stress and strain of the cladding at each moment;

[0012] (4) Based on the stress and strain of the cladding in the fuel rod and combined with the failure judgment criteria of the cladding in the fuel rod, the failure of the cladding in the fuel rod is analyzed.

[0013] Furthermore, the heat conduction calculation of the fuel pellets, cladding, and the gap between the fuel pellets and cladding in the solid fuel rod is calculated as follows:

[0014]

[0015] Where ρ is the density of the material, C p is the heat capacity of the fuel pellet or cladding, T is the temperature of the fuel pellet or cladding, τ is the time, k is the thermal conductivity of the fuel pellet or cladding, r is the distance from the centerline of the fuel pellet, and q is the heat generation rate of the fuel pellet per unit volume.

[0016] Furthermore, the coolant loss and re-flooding model in step (2) includes: from 0s to 10s, the reactor coolant flows normally, 10s later, coolant loss occurs, and it is found that the coolant level drops to zero and remains at zero for 60 seconds, then the coolant level begins to rise, and the coolants at different heights are in different phase states, when the axial position of the cladding is greater than the coolant height, the cladding exchanges heat with water vapor, and when the axial position of the cladding is lower than or equal to the coolant height, the cladding exchanges heat with cooling water.

[0017] Furthermore, in step (3), the convective heat transfer between the fuel pellet and the gas gap, the gas gap and the cladding, and the cladding and the coolant is calculated, that is,

[0018] q=h·ΔT (2)

[0019] Where q is the heat transfer per unit volume; h is the convective heat transfer coefficient of the heat transfer surface; and ΔT is the temperature difference between the two materials of the heat transfer surface.

[0020] Furthermore, the calculation of high temperature thermal creep of zirconium alloy under LOCA condition is added to the creep module of CAMPUS program:

[0021] Under LOCA conditions, the internal pressure of the fuel rod and the cladding temperature will be very high, which will lead to large creep deformation and eventually cause cladding failure, which is expressed in the form of Norton power equation:

[0022]

[0023] in, is the effective thermal creep rate at high temperature, A is in MPa -n s -1 is the strength coefficient of units, Q is the activation energy of creep deformation, σ eff is the effective stress in the cladding, n is the stress exponent, T represents the temperature of the fuel pellet or cladding: R represents the universal gas constant;

[0024] Two different methods are used to interpolate in the mixed (α+β) phase:

[0025] 1) When only the α phase is present, is an arbitrary value, and the value of A is 8737 MPa -n s -1 , the value of Q is 3.21×10 5 +24.69×

[0026] (T-9332.15)(J·mol -1 ), the value of N is 5.89;

[0027] 2) When the phase is 50% α and 50% β, consider and Situation:

[0028] a. For The value of A is 0.24MPa -n s -1 , the value of Q is 102366 J·mol -1 , the value of N is 2.33;

[0029] b. For Linear interpolation of ln(A), n, and Q was performed between the values ​​for the pure α and pure β phases;

[0030] 3) When only β phase is present, is an arbitrary value, and the value of A is 7.9 MPa -n s -1 , the value of Q is 141919 J·mol -1 , the value of N is 3.78.

[0031] Furthermore, the failure judgment criteria for the fuel rod cladding include an overstress criterion and a plastic instability criterion.

[0032] Furthermore, for the overstress criterion, it is assumed that the cladding fails when the ultimate burst stress is reached:

[0033]

[0034] Where a and b are constants obtained by interpolation between different phases; when only the α phase is present, the value of a is 830 MPa and the value of b is 1×10 -3 K -1 ; When the phase is 50% α and 50% β, the value of a is 3000 MPa and the value of b is 3×10 -3 K -1 When only the β phase is present, the value of a is 2300 MPa and the value of b is 3×10 -3 K -1 .

[0035] The current oxygen mass fraction in the cladding is estimated using the oxidation model:

[0036]

[0037] Where η is the mass fraction of oxygen in the cladding, η0 is the oxygen fraction at the time of manufacture; r cl,o and r cl,i are the outer and inner radii of the cladding, ρ Zy is the cladding density, g is the mass of oxygen, r met,o =r cl,o -S / R pb , where S is the thickness of the oxide layer, R pb =1.56.

[0038] Furthermore, for the plastic instability criterion, it is assumed that the cladding ruptures when the effective plastic strain rate reaches the limit value, and the effective plastic strain rate is 1.2×10 -3 s -1 ;

[0039] The cladding will fail when either of the overstress criterion or the plastic instability criterion is met.

[0040] Furthermore, when the calculation results meet the cladding failure criterion, the time step when the cladding fails is recorded. If the cladding failure judgment criterion is not met, the calculation is continued, and the calculation results are input as new parameters to continue calculating the temperature distribution of the fuel pellets and cladding and the stress and strain of the cladding in the next time step until the last time step. In data post-processing, starting from the cladding failure time step, the cladding effective stress is set to 0 and the gas pressure is set to the coolant pressure.

[0041] In order to achieve the second objective, a system for analyzing a pressurized water reactor solid fuel coolant loss accident is provided, comprising a heat transfer module, a solid mechanics module, a coolant loss and reflooding module, and a cladding failure determination module.

[0042] The heat transfer module is used to calculate the temperature changes and distribution of the fuel pellets, the cladding, and the gap between them;

[0043] The solid mechanics module is used to calculate the mechanical interactions, stresses and strains of the fuel pellets and cladding;

[0044] The coolant loss and reflooding module is used to simulate the coolant loss and reflooding process in a reactor coolant loss accident;

[0045] The cladding failure determination module is used to calculate the state of the fuel pellet cladding at each moment and whether it is failed.

[0046] In order to achieve the third objective, the present invention provides a storage medium storing a program, which, when executed by a processor, implements the above-mentioned method for analyzing a pressurized water reactor solid fuel coolant loss accident.

[0047] In order to achieve the fourth purpose mentioned above, the present invention provides a computing device, including a processor and a memory for storing a program executable by the processor. When the processor executes the program stored in the memory, the above-mentioned analysis method for a pressurized water reactor solid fuel coolant loss accident is implemented.

[0048] Compared with the prior art, the present invention has at least the following beneficial effects:

[0049] (1) The present invention adopts a fully coupled calculation method of heat transfer and solid mechanics, and combines the coolant loss and reflooding modules to establish the failure judgment criteria of the solid fuel cladding of the pressurized water reactor. It can accurately calculate the temperature distribution of the solid fuel cladding of the pressurized water reactor under the LOCA working condition, and then accurately calculate the stress and strain of the solid fuel cladding through multi-physical field coupling, thereby making the failure prediction of the fuel cladding more accurate.

[0050] (2) The present invention uses newer material properties and empirical models to make the calculated temperature distribution of the fuel pellets and cladding, as well as the stress and strain results of the cladding more accurate;

[0051] (3) The present invention is applicable to most fuel and cladding material coolant loss conditions, and the analysis method has a certain degree of universality.

[0052] (4) The present invention adopts the zirconium alloy failure judgment criterion, but due to the differences in material properties of different claddings, the failure judgment models are not consistent and lack universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 1 is a flow chart of a method for analyzing a loss of coolant accident in a pressurized water reactor solid fuel according to an embodiment of the present invention;

[0054] Figure 2 The change of coolant height over time for coolant loss and reflooding under LOCA-MT4 condition;

[0055] Figure 3 This is a comparison chart of the cladding failure results under LOCA conditions calculated by the present invention and the existing recorded results. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0057] Example 1

[0058] This embodiment provides a method for analyzing a loss-of-coolant accident in a pressurized water reactor solid fuel. This method uses heat conduction and convection calculations to calculate the temperature distribution of the solid fuel pellets and cladding at various times under LOCA conditions. A coolant loss and reflooding model is established, coupled with a solid mechanics module to calculate the stress and strain of the fuel cladding. Furthermore, a cladding failure model is used to analyze cladding failure.

[0059] like Figure 1 As shown, this embodiment provides a method for analyzing a loss of coolant accident for solid fuel in a pressurized water reactor. A coolant channel exists outside the solid fuel rod of the pressurized water reactor. When a loss of coolant accident occurs, the cooling efficiency of the fuel rod decreases and the temperature increases until the coolant is reflooded and cooling is restored. Heat conduction and convection calculations are used to calculate the temperature distribution of the fuel pellets and cladding at various times under LOCA conditions. A coolant loss and reflooding model is established, coupled with a solid mechanics module, to calculate the stress and strain of the fuel cladding at various locations at various times. A cladding failure model is then used to analyze cladding failure. The method specifically includes the following steps:

[0060] S1. Determine the strength parameters of the cladding material in the fuel cladding and establish a failure judgment criterion for the cladding in the fuel rod;

[0061] In this embodiment, the fuel pellets are made of uranium dioxide and the cladding is made of zirconium alloy. Of course, in other embodiments, the cladding can be made of other materials, and the physical properties and strength parameters corresponding to the materials need to be obtained.

[0062] For the overstress criterion, the cladding is assumed to fail when the ultimate burst stress is reached:

[0063]

[0064] where σ b represents the ultimate burst stress of the cladding, T represents the temperature of the fuel pellet or cladding, a and b are constants obtained by interpolation between different phases (α, β and 50% α 50% β). When only the α phase is present, the value of a is 830 MPa and the value of b is 1×10 -3 K -1 , when the phase is 50% α and 50% β, the value of a is 3000 MPa and the value of b is 3×10 -3 K -1 When only the β phase is present, the value of a is 2300 MPa and the value of b is 3×10 -3 K -1 , as shown in the following table

[0065] Table 1a and b are the constants obtained by interpolation between different phases

[0066]

[0067] η is the mass fraction of oxygen in the cladding, η0 is the oxygen fraction during manufacturing, and is taken as 1.2×10 -3 The current oxygen mass fraction in the cladding is estimated using the oxidation model:

[0068]

[0069] Among them, r cl,o and r cl,i are the outer and inner radii of the cladding, ρ Zy =6550kg·m -3 is the cladding density, g (kg·m -2 ) is the mass of oxygen, r met,o =r cl,o -S / R pb , where S(m) is the thickness of the oxide layer, R pb =1.56.

[0070] As a preferred embodiment, the calculation of high temperature thermal creep under LOCA condition is added to the creep module of CAMPUS program:

[0071] Under LOCA conditions, the internal pressure of the fuel rod and the cladding temperature will be very high, which will lead to large creep deformation and eventually cause cladding failure. Its form is Norton's power equation (taking zirconium alloy as an example):

[0072]

[0073] in, is the effective thermal creep rate at high temperature (>900K), A is in MPa -n s -1 The intensity coefficient is Q(J·mol -1 ) is the activation energy of creep deformation, σ eff (MPa) is the effective stress in the cladding, n is the stress exponent, T is the temperature of the fuel pellet or cladding, and R is the universal gas constant of 8.314 J / (mol·K);

[0074] Two different methods are used to interpolate in the mixed (α+β) phase:

[0075] 1) When only the α phase is present, is an arbitrary value, and the value of A is 8737 MPa -n s -1 , the value of Q is 3.21×10 5 +24.69×

[0076] (T-9332.15)(J·mol -1 ), the value of N is 5.89;

[0077] 2) When the phase is 50% α and 50% β, consider and Situation:

[0078] a. For The value of A is 0.24MPa -n s -1 , the value of Q is 102366 J·mol -1 , the value of N is 2.33;

[0079] b. For Linear interpolation of ln(A), n, and Q was performed between the values ​​for the pure α and pure β phases;

[0080] 3) When only β phase is present, is an arbitrary value, and the value of A is 7.9 MPa -n s -1 , the value of Q is 141919 J·mol -1 , the value of N is 3.78.

[0081] For the plastic instability criterion:

[0082] Assuming that the cladding ruptures when the effective plastic strain rate reaches the limit value, 1.2×10 -3 s -1 The value of .

[0083] The determined cladding failure criteria are as follows:

[0084] ① If a single failure criterion is met or all failure criteria are met simultaneously, the solid fuel cladding fails.

[0085] ② If all failure criteria are not met, the solid fuel cladding is normal and meets the operational requirements.

[0086] S2. Based on the solid fuel LOCA case, the relationship between coolant height and flow rate over time was determined and fitted into an empirical function. A coolant reflooding model was established, which captured the entire process of coolant loss, replenishment, and core flooding over time.

[0087] From 0s to about 10s, the coolant flows normally. Then, coolant loss occurs and the coolant level drops to zero and remains at zero for about 60 seconds. After that, the coolant level begins to rise. The coolants at different heights are in different phases. When the coolant level is greater than the coolant height, the cladding exchanges heat with water vapor. When the coolant level is less than or equal to the coolant height, the cladding exchanges heat with cooling water. Figure 2 shown.

[0088] S3. Calculating the temperature distribution of the fuel pellets and the cladding and the stress and strain of the cladding at each moment based on the linear power of the solid fuel pellets of the pressurized water reactor, the physical properties of the fuel pellets, the cladding, and the gap between the fuel pellets and the cladding, and the coolant reflooding model;

[0089] The physical properties of the gap between the fuel pellet and the cladding are the thermodynamic properties of the gas material.

[0090] The heat conduction calculation formula of the fuel pellets, cladding, and the gap between the fuel pellets and cladding in the solid fuel rod at each time is as follows:

[0091]

[0092] Where ρ is the density of the material, C p is the heat capacity of the fuel pellet or cladding, T is the temperature of the fuel pellet or cladding, τ is the time, k is the thermal conductivity of the fuel pellet or cladding, r is the distance from the centerline of the fuel pellet at each position inside the fuel pellet, and q is the heat generation rate per unit volume of the fuel pellet.

[0093] Formula (1) is used to calculate the heat transfer process and temperature distribution in the fuel pellet. As for the heat transfer process and temperature distribution in the cladding and the gap between the fuel pellet and the cladding, since there is no heat source, the source term q in Formula (1) is discarded, that is, q = 0 at this time.

[0094] The convective heat transfer between the fuel pellet and the gas gap, the gas gap and the cladding, and the cladding and the coolant is calculated, namely:

[0095] q = h·ΔT (2) where q is the heat transfer per unit volume, ΔT is the temperature difference between the two materials of the heat transfer surface, the convective heat transfer under LOCA conditions is forced convection heat transfer, and h is the convective heat transfer coefficient of the heat transfer surface. The calculation formula is as follows:

[0096]

[0097] Where k is the thermal conductivity of the fuel pellet or cladding, D is the diameter of the heat transfer surface, and Re is D is the Reynolds number; Pr is the Prandtl number, μ is the fluid dynamic viscosity, μ s is the dynamic viscosity of the cladding wall. Due to different physical properties, when the cladding axial position is greater than the coolant height, the cladding exchanges heat with water vapor, and the forced convection heat transfer coefficient is h1. When the cladding axial position is less than the coolant height, the cladding exchanges heat with cooling water, and the forced convection heat transfer coefficient is h2. Both formulas (1) and (2) are calculated using the Solid Heat Transfer Module in COMSOL.

[0098] S4. Based on the calculated temperature distribution at each location of the fuel pellet at each time, the stress and strain of the fuel rod cladding are calculated by coupling the physical fields of heat transfer and solid mechanics, and the failure of the cladding of the pressurized water reactor solid fuel is analyzed in combination with the failure judgment criteria of the fuel rod cladding;

[0099] Based on the stress and strain of the fuel pellets under LOCA conditions, a failure criterion for the solid fuel cladding is established, and based on this criterion, it is determined whether each location of the cladding has failed at each moment. The specific steps are as follows:

[0100] (1) Determine the strength parameters of the cladding material in the solid fuel cladding and establish a failure judgment criterion for the cladding in the solid fuel pellet.

[0101] (2) Based on the linear power of the solid fuel pellets, the physical properties of the fuel pellets, the cladding, and the gap between the fuel pellets and the cladding, and the coolant reflooding model, the temperature distribution of the fuel pellets and the cladding, as well as the stress and strain of the cladding at each moment under the LOCA condition, are calculated:

[0102] (3) Based on the stress and strain of the cladding in the solid fuel pellet, combined with the failure judgment of the cladding in the solid fuel pellet

[0103] Criteria for analyzing cladding failure of solid fuel pellets;

[0104] If a failure criterion is met individually or all failure criteria are met simultaneously, the cladding fails, the time step when the cladding fails is recorded and the calculation continues until the final time step.

[0105] If all failure criteria are not met, the cladding is normal and meets the operational requirements, and the calculation continues until the final time step.

[0106] Similar to the above, for each stress and strain condition of the solid fuel cladding, the conditions that need to be met for the cladding to fail are determined.

[0107] Calculations using the method provided in this embodiment first calculate the heat transfer and temperature distribution for the current time step. The stress and strain of the cladding are then calculated using a temperature-coupled solid mechanics module. The cladding failure criteria are then combined to determine whether the cladding has failed. If the cladding failure criteria are met, the time step at which the cladding failed is recorded. If the cladding failure criteria are not met, the calculation continues, using the calculated results as new parameter inputs to calculate the temperature distribution of the fuel pellets and cladding, as well as the stress and strain of the cladding, for the next time step until the final time step. In data post-processing, starting from the cladding failure time step, the cladding effective stress is set to 0, and the gas pressure is set to the coolant pressure. The solution obtained using the method described in this embodiment can serve as a reference for detailed studies of loss of coolant accidents and cladding failures in pressurized water reactors.

[0108] like Figure 3 As shown in the figure, from top to bottom are: the gas pressure and failure time results calculated by the FRAPTRAN code, the gas pressure P (MPa) and failure time results obtained by coupling heat transfer with solid mechanics in the present invention, and the gas pressure and failure time results obtained by experimental data.

[0109] According to the comparison of these graphs, the present invention has higher accuracy in calculating the failure time of the cladding under the LOCA condition.

[0110] Example 2

[0111] This embodiment provides a calculation system for the loss of coolant accident of solid fuel in a pressurized water reactor, including a heat transfer module, a solid mechanics module, a coolant loss and reflooding module, and a cladding failure determination module.

[0112] In this embodiment, the heat transfer module is used to calculate the heat generation of the fuel pellets and the heat conduction within the fuel pellets, gas, and cladding. The calculation formula is as follows:

[0113]

[0114] Where ρ is the density of the material, C pis the heat capacity of the fuel pellet or cladding, T is the uncorrected temperature of the fuel pellet or cladding, τ is time, k is the thermal conductivity of the fuel pellet or cladding, r is the distance from the centerline of the fuel pellet, and q is the heat generation rate per unit volume of the fuel pellet. Equation (1) is used to calculate the heat transfer process and temperature distribution within the fuel pellet. For the heat transfer process and temperature distribution in the cladding and the gap between the fuel pellet and cladding, since there is no heat source, the heat generation term q in Equation (1) is discarded.

[0115] The convective heat transfer between the fuel pellet and the gas gap, the gas gap and the cladding, and the cladding and the coolant is calculated, namely:

[0116] q = h·ΔT (2) where q is the heat transfer per unit volume; ΔT is the temperature difference between the two materials of the heat transfer surface; the convective heat transfer under the LOCA condition is forced convection heat transfer, and h is the forced convection heat transfer coefficient of the heat transfer surface, which is calculated as follows:

[0117]

[0118] Where k is the thermal conductivity of the fuel pellet or cladding, D is the diameter of the heat transfer surface, and Re is D is the Reynolds number; Pr is the Prandtl number; and μ is the dynamic viscosity. Due to different physical properties, when the cladding's axial position is greater than the coolant height, the cladding exchanges heat with water vapor, with a forced convection heat transfer coefficient of h1. When the cladding's axial position is less than the coolant height, the cladding exchanges heat with cooling water, with a forced convection heat transfer coefficient of h2. Equations (1) and (2) are calculated using the Solid Heat Transfer Module in COMSOL.

[0119] In this embodiment, the coolant loss and reflooding module is used to simulate the coolant loss and reflooding process in a reactor coolant loss accident. From 0s to about 10s, the coolant flows normally. Then, coolant loss occurs, the coolant level drops to zero, and remains at zero for about 60 seconds. After that, the coolant level begins to rise, and the coolants at different heights are in different phases. When the axial position of the cladding is greater than the coolant height, the cladding exchanges heat with water vapor. When the axial position of the cladding is lower than or equal to the coolant height, the cladding exchanges heat with cooling water. Figure 2 shown.

[0120] In this embodiment, the cladding failure determination module is used to determine whether each position of the cladding of the fuel pellet has failed at each moment based on the stress and strain of the cladding calculated by coupling the heat transfer and solid mechanics.

[0121] The determined cladding failure criteria are as follows:

[0122] ① If a single failure criterion is met or all failure criteria are met simultaneously, the solid fuel cladding fails.

[0123] ② If all failure criteria are not met, the solid fuel cladding is normal and meets the operational requirements.

[0124] Based on the above judgment criteria, the calculation system is used to judge whether the cladding has failed.

[0125] Example 3

[0126] This embodiment also provides a storage medium, which can be a ROM, RAM, magnetic disk, optical disk or other storage medium. The storage medium stores one or more programs. When the program is executed by the processor, the analysis method of the pressurized water reactor solid fuel coolant loss accident of the above-mentioned embodiment 1 is implemented.

[0127] Example 4

[0128] This embodiment provides a computing device, which can be a desktop computer, a laptop computer, a smart phone, a PDA handheld terminal, a tablet computer, or other terminal device with a display function. The computing device includes a processor and a memory, and the memory stores one or more programs. When the processor executes the program stored in the memory, the analysis method for the loss of solid fuel coolant accident of a pressurized water reactor described in the above-mentioned embodiment 1 is implemented.

[0129] An embodiment of the present invention provides a method for analyzing a loss of coolant accident in a pressurized water reactor solid fuel. The solid fuel is uranium dioxide fuel, and the cladding material is zirconium alloy. The fuel properties of the fuel are calculated based on the LOCA-MT4 case. Based on this calculation, the cladding failure in the fuel pellet is calculated using stress failure criteria and plastic strain failure criteria, and the process is modified. The present invention develops a solid fuel loss of coolant accident calculation model and implements a coolant reflooding model for LOCA conditions, resulting in more accurate calculations using the present invention.

[0130] The embodiment of the present invention can achieve the effect of rapid modeling and calculation of various fuel and cladding materials by using COMSOL to quickly adjust the material properties of solid fuel pellet fuel and cladding on an existing solid fuel model.

[0131] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for analyzing a loss of coolant accident in a pressurized water reactor solid fuel, characterized in that: The following steps are involved: (1) determining the strength parameters of the cladding material in the pressurized water reactor fuel rod and establishing a failure judgment criterion for the cladding in the fuel rod; the failure judgment criterion for the cladding in the fuel rod includes an overstress criterion and a plastic instability criterion; For the overstress criterion, the cladding is assumed to fail when the ultimate burst stress is reached: Where a and b are constants obtained by interpolation between different phases; when only the α phase is present, the value of a is 830 MPa and the value of b is 1×10 -3 K -1 ; When the phase is 50% α and 50% β, the value of a is 3000 MPa and the value of b is 3×10 -3 K -1 When only the β phase is present, the value of a is 2300 MPa and the value of b is 3×10 -3 K -1 ; The current oxygen mass fraction in the cladding is estimated using the oxidation model: Where η is the mass fraction of oxygen in the cladding, η0 is the oxygen fraction at the time of manufacture; r cl,o and r cl,i are the outer and inner radii of the cladding, ρ Zy is the cladding density, g is the mass of oxygen, r met,o =r cl,o -S / R pb , where S is the thickness of the oxide layer, R pb =1.56; (2) Based on the solid fuel LOCA case, the relationship between coolant height and flow rate over time is determined and fitted into an empirical function to establish a coolant loss and reflooding model, realizing the entire process of coolant loss, replenishment, and reflooding over time; The calculation of high temperature thermal creep of zirconium alloy under LOCA condition is added to the creep module of CAMPUS program: Under LOCA conditions, the internal pressure of the fuel rod and the cladding temperature will be very high, which will lead to large creep deformation and eventually cause cladding failure, which is expressed in the form of Norton power equation: in, is the effective thermal creep rate at high temperature, A is in MPa -n s -1 is the strength coefficient of units, Q is the activation energy of creep deformation, σ eff is the effective stress in the cladding, n is the stress exponent, T represents the temperature of the fuel pellet or cladding: R represents the universal gas constant; Two different methods are used to interpolate in the mixed (α+β) phase: 1) When only the α phase is present, is an arbitrary value, and the value of A is 8737 MPa -n s -1 , the value of Q is 3.21×10 5 +24.69×(T-9332.15)(J·mol -1 ), the value of N is 5.89; 2) When the phase is 50% α and 50% β, consider and Situation: a. The value of A is 0.24MPa -n s -1 , the value of Q is 102366 J·mol -1 , the value of N is 2.33; b. For Linear interpolation of ln(A), n, and Q was performed between the values ​​for the pure α and pure β phases; 3) When only β phase is present, is an arbitrary value, and the value of A is 7.9 MPa -n s -1 , the value of Q is 141919 J·mol -1 , the value of N is 3.78; (3) Based on the fuel pellet linear power and the physical properties of the fuel pellet, cladding, and the gap between the fuel pellet and the cladding, the coolant loss and reflooding model calculates the temperature distribution of the fuel pellet and the cladding, as well as the stress and strain of the cladding at each moment; (4) Based on the stress and strain of the cladding in the fuel rod and combined with the failure judgment criteria of the cladding in the fuel rod, the failure of the cladding in the fuel rod is analyzed.

2. The method for analyzing a loss of coolant accident in a pressurized water reactor solid fuel according to claim 1, characterized in that: The heat conduction calculation of the fuel pellets, cladding, and the gap between the fuel pellets and cladding in a solid fuel rod is calculated as follows: Where ρ is the density of the material, C p is the heat capacity of the fuel pellet or cladding, T is the temperature of the fuel pellet or cladding, τ is the time, k is the thermal conductivity of the fuel pellet or cladding, r is the distance from the centerline of the fuel pellet, and q is the heat generation rate of the fuel pellet per unit volume.

3. The method for analyzing a loss of coolant accident in a pressurized water reactor solid fuel according to claim 1, characterized in that: The coolant loss and re-flooding model in step (2) includes: from 0s to 10s, the reactor coolant flows normally, 10s later, coolant loss occurs, and the coolant level is found to drop to zero and remains at zero for 60 seconds, after which the coolant level begins to rise. Coolants at different heights are in different phase states, and when the axial position of the cladding is greater than the coolant height, the cladding exchanges heat with water vapor, and when the axial position of the cladding is lower than or equal to the coolant height, the cladding exchanges heat with cooling water.

4. The method for analyzing a loss of coolant accident in a pressurized water reactor solid fuel according to claim 1, wherein: In step (3), the convective heat transfer between the fuel pellet and the gas gap, the gas gap and the cladding, and the cladding and the coolant is calculated, that is, q=h*ΔT Where q is the heat transfer per unit volume; h is the convective heat transfer coefficient of the heat transfer surface; and ΔT is the temperature difference between the two materials of the heat transfer surface.

5. The method for analyzing a loss of coolant accident in a pressurized water reactor solid fuel according to claim 1, characterized in that: For the plastic instability criterion, it is assumed that the cladding ruptures when the effective plastic strain rate reaches the limit value, and the effective plastic strain rate is 1.2×10 -3 s -1 ; The cladding will fail when either of the overstress criterion or the plastic instability criterion is met.

6. The method for analyzing a loss of coolant accident in a pressurized water reactor solid fuel according to claim 1, characterized in that: When the calculation results meet the cladding failure criterion, the time step when the cladding fails is recorded. If the cladding failure criterion is not met, the calculation is continued and the calculation results are used as new parameters to input the temperature distribution of the fuel pellets and cladding and the stress and strain of the cladding in the next time step until the last time step. In data post-processing, starting from the cladding failure time step, the cladding effective stress is set to 0 and the gas pressure is set to the coolant pressure.

7. A system for implementing the method for analyzing a loss of coolant accident in a pressurized water reactor solid fuel according to any one of claims 1 to 6, characterized in that: Including heat transfer module, solid mechanics module, coolant loss and reflooding module, cladding failure determination module; The heat transfer module is used to calculate the temperature changes and distribution of the fuel pellets, the cladding, and the gap between them; The solid mechanics module is used to calculate the mechanical interactions, stresses and strains of the fuel pellets and cladding; The coolant loss and reflooding module is used to simulate the coolant loss and reflooding process in a reactor coolant loss accident; The cladding failure determination module is used to calculate the state of the fuel pellet cladding at each moment and whether it is failed.

Images