Core thermal-hydraulic parameter calculation method for pressurized water reactor annular fuel assembly loading

Abstract

A kind of method for calculating the thermal-hydraulic parameters of pressurized water reactor (PWR) core loaded with annular fuel assemblies, comprising the following steps: first, constructing a physical model of the PWR core loaded with annular fuel assemblies, and obtaining a three-dimensional power distribution of the core by using a core physics calculation program; second, initializing the flow distribution coefficients and heat distribution coefficients of all the inner and outer channels of the annular fuel assemblies; third, calculating the coolant temperature of the inner and outer channels of the annular fuel assemblies according to the power; fourth, calculating the temperature distribution of the annular fuel assemblies according to the coolant temperature, updating the heat distribution coefficients of the inner and outer channels, and repeating the above steps until the heat distribution coefficients of the inner and outer channels converge; fifth, calculating the pressure drop of the inner and outer channels, updating the flow distribution coefficients of the inner and outer channels according to the principle of consistent pressure drop, and repeating the above steps until the flow distribution coefficients of the inner and outer channels converge, and updating the calculation results of the thermal-hydraulic parameters of the core. The present application provides a new method for calculating the thermal-hydraulic parameters of the PWR core loaded with annular fuel assemblies.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pressurized water reactor core physics calculation, and in particular to a method for calculating thermal-hydraulic parameters of a pressurized water reactor core loaded with annular fuel assemblies. BACKGROUND

[0002] The existing method for calculating thermal-hydraulic parameters of a pressurized water reactor core is only applicable to solid rod fuel, and existing methods cannot solve the new thermal-hydraulic parameter calculation problem of annular fuel due to its special geometric structure. The annular fuel rod adds an internal coolant channel, and there are three new problems: first, compared with the single-sided cooling process of rod fuel rods, the annular fuel rod is cooled by the coolant on both sides of the inner and outer channels, and a double-sided heat conduction model needs to be used to calculate the fuel rod temperature distribution when performing thermal-hydraulic parameter calculation; second, the thermal power of the rod fuel rod is completely transferred to one coolant channel, and the annular fuel rod adds an internal coolant channel, so the thermal power of the annular fuel rod needs to be distributed to the inner and outer channels; third, the temperature distribution of the rod fuel rod in the coolant channel is only related to the coolant flow at the inlet, and under the condition that the coolant flow at the inlet of the annular fuel rod is constant, the influence of the coolant flow distribution in the inner and outer channels of the fuel rod on the calculation of the coolant temperature also needs to be considered. The existing method is mainly used to solve the thermal-hydraulic parameters of traditional rod fuel, and lacks special research on the thermal-hydraulic parameter calculation method for a core loaded with annular fuel assemblies. SUMMARY

[0003] In order to overcome the problems existing in the prior art, the purpose of the present application is to provide a method for calculating thermal-hydraulic parameters of a pressurized water reactor core loaded with annular fuel assemblies, which accurately obtains the fuel temperature distribution of the annular fuel rod and the coolant temperature distribution in the inner and outer channels of the annular fuel rod by considering the heat conduction of the annular fuel rod and the consistent fluid pressure drop in the inner and outer channels of the annular fuel rod.

[0004] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0005] A method for calculating thermal-hydraulic parameters of a pressurized water reactor core loaded with annular fuel assemblies, comprising the following steps:

[0006] Step 1: Construct a pressurized water reactor core physics model loaded with annular fuel assemblies, and obtain the three-dimensional power distribution information of the core by using a core physics calculation program;

[0007] 1) According to the modeling parameters of the annular fuel assembly, including the geometric and material information of the annular fuel rod, the burnable poison rod, the control rod, the guide tube, the instrument tube and other structures, and the arrangement information of the annular fuel assembly in the core, a pressurized water reactor core physics model loaded with annular fuel assemblies is constructed;

[0008] 2) The core physics calculation program is used to perform neutron calculation on the core physical model of the pressurized water reactor to obtain three-dimensional power distribution information of the core.

[0009] Step 2: Initialize the flow distribution coefficients and heat distribution coefficients of all the inner and outer channels of the annular fuel rods in the annular fuel assembly;

[0010] 1) The flow distribution coefficients of the inner and outer channels of all the annular fuel rods in the annular fuel assembly are initialized, and the initial assumption is that the mass flow distribution ratio of the coolant in the inner and outer channels is proportional to the cross-sectional area ratio of the channels;

[0011] 2) In combination with the three-dimensional power distribution information of the core, the power of the annular fuel rod is evenly distributed in the initial state, and the coolant in the inner and outer channels obtains 50% of the heat of the annular fuel rod power.

[0012] The initialization of the flow distribution coefficients and heat distribution coefficients of the inner and outer channels of the annular fuel rod is close to the objective physical condition, which is conducive to the development of the core thermal-hydraulic parameter iteration calculation and the rapid solution of the two to-be-solved coefficients.

[0013] Step 3: Perform coolant temperature calculation of the inner and outer channels of the annular fuel rods in the annular fuel assembly according to the three-dimensional power distribution information of the core;

[0014] According to the annular fuel heat distribution coefficient and the three-dimensional power distribution information of the core, the coolant temperature of the inner and outer channels of all the annular fuel rods in the annular fuel assembly is calculated; the annular fuel rod is grid-divided in the axial direction, and the coolant enthalpy rise calculation is sequentially performed from the bottom grid to the top grid to determine the coolant enthalpy value distribution; the coolant temperature distribution of the inner and outer channels of all the annular fuel rods in the annular fuel assembly is determined through the coolant enthalpy value distribution, and the core coolant temperature distribution calculation can be accurately and efficiently performed through the sequential calculation of all the fuel rods in the annular fuel assembly from the bottom to the top. The coolant enthalpy rise calculation is shown in formula (1):

[0015] Formula (1)

[0016] In the formula:

[0017] Hin is the coolant enthalpy value at the outlet of the inner coolant channel of the annular fuel rod;

[0018] Hout is the coolant enthalpy value at the inlet of the outer coolant channel of the annular fuel rod;

[0019] Hin is the coolant enthalpy value at the outlet of the inner coolant channel of the annular fuel rod;

[0020] — is the coolant enthalpy at the inlet of the annular fuel rod internal coolant channel;

[0021] — is the annular fuel rod heat partition coefficient;

[0022] — is the linear power density of the segment of the annular fuel rod;

[0023] — is the axial height of the segment of the annular fuel rod;

[0024] — is the average coolant density;

[0025] — is the average coolant velocity.

[0026] Step 4: Perform the temperature distribution calculation of the annular fuel rod according to the coolant temperature of the inner and outer channels of the annular fuel assembly, update the inner and outer channel heat partition coefficients, and return to Step 3 until the inner and outer channel heat partition coefficients converge; this step not only can calculate the temperature distribution and heat partition coefficient of the annular fuel rod at the same time, but also can improve the overall iterative calculation efficiency by taking the calculation deviation of the heat partition coefficient in the adjacent iteration step as the convergence criterion;

[0027] 1) Establish a heat conduction model for the double-sided cooling structure of the annular fuel rod: take the coolant temperature of the inner and outer channels of the annular fuel rod as the boundary condition to perform the heat conduction calculation of the annular fuel rod, and obtain the temperature distribution of the annular fuel rod; the annular fuel rod has rotational symmetry with any angle around the center in the radial direction, so the heat conduction process of the annular fuel rod is represented as a discrete form of one-dimensional heat conduction model, and the radial one-dimensional heat conduction model of the annular fuel rod is shown in formula (2), and the heat exchange mode between the fuel and the coolant is shown in formula (3);

[0028] Formula (2)

[0029] Formula (3)

[0030] In the formula:

[0031] r— is the heat conduction calculation position of the annular fuel rod;

[0032] k(r)— is the thermal conductivity of the material at position r;

[0033] q(r)— is the power density of the material at position r;

[0034] T(r)— is the temperature at position r;

[0035] q' - is the convective heat transfer density at the surface of the annular fuel rod;

[0036] h - is the convective heat transfer coefficient;

[0037] ΔΤ - is the temperature difference between the fuel and the coolant at the surface of the annular fuel rod;

[0038] 2) Since the annular fuel rod in the annular fuel assembly is cooled by the coolant in the inner channel and the outer channel at the same time, the radial temperature will show the approximate parabolic distribution characteristics of low temperature at both ends and high temperature in the middle. Taking the adiabatic surface of the annular fuel rod as the radial temperature peak, the heat distribution coefficient of the annular fuel rod is updated and calculated, and the heat distribution coefficient calculation method is shown in formula (4);

[0039] Formula (4)

[0040] In the formula:

[0041] - is the heat distribution coefficient of the annular fuel rod;

[0042] - is the outer boundary radius of the fuel pellet in the annular fuel rod;

[0043] - is the inner boundary radius of the fuel pellet in the annular fuel rod;

[0044] - is the radius of the adiabatic surface of the annular fuel rod;

[0045] After updating the heat distribution coefficient, return to step 3 to recalculate the coolant temperature until the heat distribution coefficient of the annular fuel rod converges, and then proceed to the next step.

[0046] The convergence criterion of the heat distribution coefficient of the annular fuel rod is that the relative deviation of the heat distribution coefficient of the annular fuel rod in the two iteration calculation processes is within 1%. This iteration convergence criterion can ensure the calculation accuracy while taking into account the calculation efficiency.

[0047] Step 5: Calculate the inner channel pressure drop and the outer channel pressure drop for the annular fuel rod, update the inner and outer channel coolant flow distribution coefficient according to the principle of consistent inner and outer channel pressure drop, and return to step 3 to calculate the coolant temperature distribution and the annular fuel rod temperature distribution under the updated annular fuel rod inner and outer channel coolant mass flow, until the inner and outer channel coolant flow distribution coefficient converges, and the core thermal hydraulic parameter calculation result, i.e. the annular fuel rod temperature distribution and the coolant temperature distribution, is updated;

[0048] 1) The coolant flow distribution ratio in the inner and outer channels of the annular fuel rod will affect the heat transfer process of the annular fuel under the condition that the coolant mass flow rate at the annular fuel rod inlet is unchanged; the coolant flow distribution in the inner and outer channels is based on the same coolant flow pressure drop in the inner and outer channels of the annular fuel rod in the reactor core; this step is based on the objective physical phenomenon of coolant flow in the annular fuel rod as the coolant flow distribution criterion in the inner and outer channels, to ensure the rationality and accuracy of the calculation; wherein the coolant flow pressure drop calculation method is shown in formula (5);

[0049] Formula (5)

[0050] In the formula,

[0051] Total flow pressure drop in the coolant channel;

[0052] Fluid lifting pressure drop in the coolant channel;

[0053] Friction resistance pressure drop in the coolant channel;

[0054] Local resistance pressure drop in the coolant channel;

[0055] 2) Adjust the coolant flow distribution share of the inner and outer channels of the annular fuel rod, that is, the coolant flow distribution coefficient, re-execute step 3, and calculate the coolant temperature distribution and the annular fuel rod temperature distribution under the updated coolant mass flow rate of the inner and outer channels of the annular fuel rod, until the coolant flow distribution coefficient of the inner and outer channels of the annular fuel rod converges, that is, the coolant flow pressure drops in the inner and outer channels are the same; because the influence of the temperature distribution and the heat distribution coefficient of the annular fuel rod on the coolant flow state in the inner and outer channels is considered, the calculation process of the coolant flow distribution coefficient is more reasonable;

[0056] 3) Based on the above process, the thermal-hydraulic parameter calculation of the reactor core loaded with annular fuel assemblies is completed, including the temperature distribution and the coolant temperature distribution of all annular fuel rods in the annular fuel assemblies in the whole reactor core and other key parameters.

[0057] Compared with the prior art, the present application has the following advantages:

[0058] 1) The present application establishes an iterative flow distribution coefficient process based on the principle of consistent pressure drop in the inner and outer channels, more accurately gives the flow in the inner and outer channels of all annular fuel rods in the annular fuel assembly and the temperature distribution of the coolant from the objective physical point of view, and avoids the basic principle that the flow distribution result does not satisfy the consistent pressure drop in the inner and outer channels.

[0059] 2), The application establishes a heat conduction model for the annular fuel rod, can accurately obtain the temperature distribution of the annular fuel rod under the condition of simultaneous cooling of the inner channel and the outer channel, and can give the specific position of the adiabatic surface, so as to provide accurate heat distribution coefficients and avoid errors introduced by inaccurate calculation of the adiabatic surface position. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 The specific implementation steps of the application are shown in the flow chart.

[0061] Figure 2 Annular fuel radial one-dimensional temperature distribution diagram.

[0062] Figure 3 Annular fuel rod inner and outer channel coolant temperature distribution. DETAILED DESCRIPTION

[0063] The application will be further described in detail below in combination with the drawings and specific embodiments.

[0064] The application provides a method for calculating thermal-hydraulic parameters of a pressurized water reactor (PWR) annular fuel assembly loaded core, which can calculate the temperature distribution of the annular fuel rod, the inner and outer coolant heat distribution of the annular fuel pellet fission heat, and the coolant flow distribution in the inner and outer channels of all annular fuel rods in the annular fuel assembly. A core physical model of the annular fuel assembly loaded PWR is constructed, and a core physical calculation program is used to obtain three-dimensional power distribution information of the core; the coolant temperature in the inner and outer channels of the annular fuel assembly is calculated; the coolant temperature is used as a boundary condition to solve the temperature distribution of the annular fuel rod, the temperature peak is taken as an adiabatic surface, the heat power of the annular fuel rod is redistributed to the coolant in the inner and outer channels, and the temperature distribution of the annular fuel rod is recalculated, the heat distribution coefficient is updated until the heat distribution coefficient converges; finally, the flow distribution coefficient in the inner and outer channels is adjusted according to the same pressure drop of the coolant in the inner and outer channels of the annular fuel assembly, until the pressure drops of the coolants in the inner and outer channels are equal, and the core thermal-hydraulic parameter calculation result is updated. The specific implementation steps are shown in Figure 1 , including the following steps:

[0065] Step 1: Construct a PWR core physical model loaded with an annular fuel assembly, and use a core physical calculation program to obtain three-dimensional power distribution information of the core;

[0066] 1) Firstly, according to the modeling parameters of the annular fuel assembly, including the geometric and material information of the annular fuel rod, burnable poison rod, control rod, guide tube, instrument tube and other structures, the assembly calculation program LOCUST in the advanced pressurized water reactor core physics analysis software Bamboo-C is used to build the annular fuel assembly model and the reflector assembly model, which are collectively referred to as the assembly physical model; and then, according to the modeling parameters of the pressurized water reactor core loaded with the annular fuel assembly, including the different annular fuel assembly arrangement information of the core, the core geometric size, the control rod information, the coolant setting information, and the cold-state model parameters of the annular fuel assembly, the core calculation program SPARK in the advanced pressurized water reactor core physics analysis software Bamboo-C is used to build the pressurized water reactor core physical model.

[0067] 2) The advanced pressurized water reactor core physics analysis software Bamboo-C is used to perform neutron calculation on the pressurized water reactor core physical model to obtain the three-dimensional power distribution information of the core.

[0068] Step 2: Initialize the flow distribution coefficients and heat distribution coefficients of all annular fuel rods in the annular fuel assembly;

[0069] 1) The flow distribution coefficients of the inner channel and the outer channel of all annular fuel rods in the annular fuel assembly are initialized, and the initial assumption is that the mass flow distribution ratio of the coolant in the inner and outer channels is proportional to the cross-sectional area ratio of the channels;

[0070] 2) Combined with the three-dimensional power distribution information of the core, the power of the annular fuel rod is evenly distributed in the initial state, and the heat received by the coolant in the inner and outer channels accounts for 50% of the power of the annular fuel rod.

[0071] Step 3: According to the heat distribution coefficients of the annular fuel and the power distribution of the annular fuel rod in the three-dimensional power distribution information of the core, the coolant temperature in the inner and outer channels of all annular fuel rods in the annular fuel assembly is calculated. Among them, the annular fuel rod is divided into grids in the axial direction using the core calculation program SPARK, and the coolant enthalpy value distribution is determined by sequentially calculating the coolant enthalpy in the axial direction of the annular fuel rod from the bottom to the top; the temperature distribution of the coolant in the inner and outer channels of all annular fuel rods in the annular fuel assembly is determined by the coolant enthalpy value distribution, and the coolant enthalpy calculation is shown in formula (1):

[0072] Formula (1)

[0073] In the formula:

[0074] — is the coolant enthalpy value at the outlet of the outer coolant channel of the annular fuel rod;

[0075] — is the coolant enthalpy value at the inlet of the outer coolant channel of the annular fuel rod;

[0076] — is the coolant enthalpy at the outlet of the inner coolant channel of the annular fuel rod;

[0077] — is the coolant enthalpy at the inlet of the inner coolant channel of the annular fuel rod;

[0078] — is the heat partition coefficient of the annular fuel rod;

[0079] — is the linear power density of the segment of the annular fuel rod;

[0080] — is the axial height of the segment of the annular fuel rod;

[0081] — is the average coolant density;

[0082] — is the average coolant velocity.

[0083] Step 4: Perform the temperature distribution calculation of the annular fuel rod according to the coolant temperature of the inner channel and the outer channel of the annular fuel assembly, update the heat partition coefficient of the inner and outer channels, and return to Step 3 until the heat partition coefficient of the inner and outer channels converges;

[0084] 1) Perform the heat conduction calculation of the annular fuel rod with the coolant temperature of the inner channel and the outer channel of the annular fuel assembly as the boundary condition to obtain the temperature distribution of the annular fuel rod. The annular fuel rod has rotational symmetry of any angle with the center as the rotation point in the radial direction, so the heat conduction process of the annular fuel rod can be represented as a one-dimensional heat conduction model in discrete form; finally, the heat conduction model of the annular fuel rod and the heat exchange method between the fuel and the coolant are embedded into the core calculation program SPARK; wherein the radial one-dimensional heat conduction model of the annular fuel rod is shown in formula (2), and the heat exchange method between the fuel and the coolant is shown in formula (3).

[0085] Formula (2)

[0086] Formula (3)

[0087] In the formula:

[0088] r— is the heat conduction calculation position of the annular fuel rod;

[0089] k(r)— is the thermal conductivity of the material at position r;

[0090] q(r)— is the power density of the material at position r;

[0091] T(r) - temperature at position r;

[0092] q' - convective heat transfer density at the surface of the annular fuel rod;

[0093] h - convective heat transfer coefficient;

[0094] ΔT - temperature difference between the fuel and the coolant at the surface of the annular fuel rod;

[0095] 2) Since the annular fuel rod in the annular fuel assembly is simultaneously cooled by the coolant in the inner channel and the outer channel, the radial temperature will exhibit an approximate parabolic distribution characteristic of low temperature at both ends and high temperature in the middle. Taking the adiabatic surface at the peak of the radial temperature of the annular fuel rod as an example, the heat distribution coefficient of the annular fuel rod is updated and calculated, and the heat distribution coefficient of the original use is replaced by the heat distribution coefficient calculated by the core calculation program SPARK according to the adiabatic surface position and the modeling information of the annular fuel rod. The heat distribution coefficient calculation method is shown in formula (4).

[0096] Formula (4)

[0097] In the formula:

[0098] - heat distribution coefficient of the annular fuel rod;

[0099] - outer boundary radius of the fuel pellet in the annular fuel rod;

[0100] - inner boundary radius of the fuel pellet in the annular fuel rod;

[0101] - radius of the adiabatic surface of the annular fuel rod;

[0102] After updating the heat distribution coefficient, return to step 3 to recalculate the coolant temperature until the heat distribution coefficient of the annular fuel rod converges, i.e. the relative deviation of the heat distribution coefficient of the annular fuel rod changes within 1% in the two iteration calculation processes. The next step can be performed.

[0103] Step 5: Calculate the inner channel pressure drop and the outer channel pressure drop for the annular fuel rod, update the inner and outer channel coolant flow distribution coefficient according to the principle of consistent inner and outer channel pressure drop, and return to step 3 to calculate the coolant temperature distribution and the annular fuel rod temperature distribution under the updated annular fuel rod inner and outer channel coolant mass flow, until the inner and outer channel coolant flow distribution coefficient converges, and update the core thermal hydraulic parameter calculation result, i.e. the annular fuel rod temperature distribution and the coolant temperature distribution;

[0104] 1) The coolant flow distribution ratio in the inner and outer channels of the annular fuel rod will affect the heat transfer process of the annular fuel under the condition that the coolant mass flow rate at the annular fuel rod inlet is constant. Here, the flow distribution in the inner and outer channels of the annular fuel rod is based on the same coolant flow pressure drop in the inner and outer channels of the annular fuel rod in the core. The flow pressure drop calculation method of the coolant in the inner and outer channels of the annular fuel rod is embedded into the core calculation program SPARK. Under the condition that the coolant flow rate at the annular fuel rod inlet is constant, the coolant distribution coefficient in the inner and outer channels of the annular fuel rod is continuously adjusted and the deviation of the flow pressure drop of the coolant in the inner and outer channels of the annular fuel rod is compared. When the relative deviation of the coolant flow pressure drop between the inner and outer channels is less than one thousandth, the flow pressure drop is considered to be the same, and the coolant flow distribution coefficient in the inner and outer channels at this time is saved, wherein the coolant flow pressure drop calculation method is shown in formula (5).

[0105] Formula (5)

[0106] In the formula:

[0107] Total flow pressure drop in the coolant channel;

[0108] Fluid lifting pressure drop in the coolant channel;

[0109] Friction resistance pressure drop in the coolant channel;

[0110] Local resistance pressure drop in the coolant channel;

[0111] The coolant flow distribution share of the inner and outer channels of the annular fuel rod, i.e. the coolant flow distribution coefficient, is adjusted, step 3 is re-executed, the coolant temperature distribution and the annular fuel rod temperature distribution are calculated under the updated coolant mass flow rate in the inner and outer channels of the annular fuel rod, and the coolant flow pressure drop in the inner and outer channels of the annular fuel rod is calculated until the coolant flow pressure drop in the inner and outer channels of the annular fuel rod is the same.

[0112] 2) The thermal-hydraulic parameter calculation of the annular fuel assembly loaded core is completed based on the above process using the core calculation program SPARK in the advanced pressurized water reactor core physics analysis software Bamboo-C, which includes key parameters such as the annular fuel rod temperature distribution and the coolant temperature distribution in the annular fuel assembly of the full core.

[0113] In this example, the core calculation program SPARK in the advanced pressurized water reactor core physics analysis software Bamboo-C is used to simulate and calculate the annular fuel loaded core, and the calculation method of the thermal-hydraulic parameters of the annular fuel assembly loaded core in the present application is as follows: Figure 1The radial temperature distribution of the annular fuel rod calculated by the heat conduction model for the annular fuel rod proposed by the present application is shown in the flow chart, wherein the left three temperature points of the temperature distribution diagram are the inner can temperature of the annular fuel rod, the right three temperature points are the outer can temperature of the annular fuel rod, and the approximately parabolic shape in the middle is the temperature distribution of the fuel pellet, the temperature distribution characteristics of each structure of the annular fuel rod are consistent with the actual situation, which shows that the method of the present application can obtain accurate fuel rod temperature distribution under the condition of simultaneous cooling of the inner channel and the outer channel. Figure 2 The temperature distribution of the coolant after distribution in the inner channel and the outer channel of the annular fuel assembly is shown in Figure 3 The coolant flowing in the inner channel and the outer channel of the annular fuel rod is heated respectively after the flow distribution of the coolant in the inner channel and the outer channel and the heat distribution of the fuel rod, and the maximum temperature difference absolute value of the inner channel and the outer channel at the top outlet of the fuel rod is below 5K, which is small, and is consistent with the requirement that the fuel rod has good cooling performance in the design of the annular fuel assembly, further illustrating the accuracy of the calculation of the heat distribution coefficient and the flow distribution coefficient of the annular fuel rod.

Claims

1. A method for calculating thermal hydraulic parameters of a pressurized water reactor annular fuel assembly loading core, characterized by: The steps include: Step 1: Construct a physical model of the PWR core loaded with annular fuel assemblies and use a core physics calculation program to obtain the three-dimensional power distribution information of the core; Step 2: Initialize the flow distribution coefficients and heat distribution coefficients of the inner and outer channels of all annular fuel rods in the annular fuel assembly; Step 3: Calculate the coolant temperature of the inner and outer channels of the annular fuel rods in the annular fuel assembly based on the three-dimensional power distribution information of the core; Step 4: Calculate the temperature distribution of the annular fuel rod based on the coolant temperatures of the inner and outer channels of the annular fuel rod in the annular fuel assembly, update the heat distribution coefficients of the inner and outer channels, and return to Step 3 until the heat distribution coefficients of the inner and outer channels converge. Step 5: Calculate the inner and outer channel pressure drops for the annular fuel rods. Update the inner and outer channel coolant flow distribution coefficients based on the principle that the inner and outer channel pressure drops are consistent. Return to step 3 and calculate the coolant temperature distribution and the annular fuel rod temperature distribution at the updated inner and outer channel coolant mass flow rates until the inner and outer channel coolant flow distribution coefficients converge. Then update the core thermal-hydraulic parameter calculation results, namely the annular fuel rod temperature distribution and the coolant temperature distribution. The implementation process of step 1 is as follows: 1) Based on the modeling parameters of the annular fuel assembly, including the geometry and material information of the annular fuel rods, burnable poison rods, control rods, guide tubes, and instrument tubes, as well as the layout information of the annular fuel assembly in the core, a physical model of the pressurized water reactor core loaded with the annular fuel assembly is constructed; 2) Using a core physics calculation program to perform neutronics calculations on the PWR core physical model to obtain three-dimensional core power distribution information; The implementation process of step 3 is as follows: Based on the annular fuel heat distribution coefficient and the three-dimensional power distribution information of the core, the coolant temperature of the inner and outer channels of all annular fuel rods in the annular fuel assembly is calculated. The annular fuel rods are meshed in the axial direction, and the coolant enthalpy rise is calculated from the bottom mesh to the top mesh to determine the coolant enthalpy value distribution. The coolant temperature distribution of the inner and outer channels of all annular fuel rods in the annular fuel assembly is determined based on the coolant enthalpy value distribution. The coolant enthalpy rise calculation is shown in formula (1): Formula (1) Where: ——is the coolant enthalpy at the outlet of the external coolant channel of the annular fuel rod; ——is the coolant enthalpy at the inlet of the external coolant channel of the annular fuel rod; ——is the coolant enthalpy at the outlet of the coolant channel inside the annular fuel rod; ——is the coolant enthalpy at the inlet of the coolant channel inside the annular fuel rod; ——is the heat distribution coefficient of the annular fuel rod; ——is the linear power density of the annular fuel rod; ——is the axial height of the annular fuel rod; — average density of coolant; — average coolant velocity; The implementation process of step 4 is as follows: 1) A heat conduction model is established for the bilateral cooling structure of the annular fuel rod: the heat conduction of the annular fuel rod is calculated using the coolant temperatures of the inner and outer channels of the annular fuel rod as boundary conditions to obtain the radial temperature distribution of the annular fuel rod. The annular fuel rod has rotational symmetry at any angle in the radial direction with the center of the circle as the rotation point. Therefore, the heat conduction process of the annular fuel rod is represented by a one-dimensional heat conduction model. The radial one-dimensional heat conduction model of the annular fuel rod is shown in formula (2), and the heat transfer mode between the fuel and the coolant is shown in formula (3). Formula (2) Formula (3) Where: r——is the heat conduction calculation position of the annular fuel rod; k(r) – is the thermal conductivity of the material at position r; q(r) – is the material power density at position r; T(r) – is the temperature at position r; q' is the convective heat transfer density at the surface of the annular fuel rod; h——convective heat transfer coefficient; ——is the temperature difference between the fuel and coolant at the surface of the annular fuel rod; 2) Since the annular fuel rods in the annular fuel assembly are cooled by the coolant in both the inner and outer channels, the radial temperature will show a nearly parabolic distribution characteristic with low temperatures on both sides and high temperatures in the middle. The peak temperature of the annular fuel rod in the radial direction is used as the insulation surface, and the heat distribution coefficient of the thermal power of the annular fuel rod in the inner and outer channels is updated and calculated. The heat distribution coefficient calculation method is shown in formula (4). Formula (4) Where: — heat distribution coefficient of annular fuel rod; — the outer boundary radius of the fuel pellets in an annular fuel rod; — the inner boundary radius of the fuel pellets in an annular fuel rod; —Radius of the insulating surface of the annular fuel rod; After updating the heat distribution coefficient, return to step 3 and recalculate the coolant temperature until the heat distribution coefficient of the annular fuel rod converges, and then proceed to the next step.

2. The method according to claim 1, wherein: The implementation process of step 2 is as follows: 1) Initialize the flow distribution coefficients of the inner and outer channels of all annular fuel rods in the annular fuel assembly. The initial assumption is that the mass flow distribution ratio of the coolant in the inner and outer channels is proportional to the ratio of the channel cross-sectional areas. 2) Based on the three-dimensional power distribution information of the core, the power of the annular fuel rods is evenly distributed in the initial state, and the heat obtained by the coolant in the inner and outer channels each accounts for 50% of the annular fuel rod power.

3. The method according to claim 1, wherein: The convergence criterion of the heat distribution coefficient of the annular fuel rod is that the relative deviation of the heat distribution coefficient of the annular fuel rod is within 1% during two iterative calculation processes.

4. The method according to claim 1, wherein: The implementation process of step 5 is as follows: 1) When the coolant mass flow rate at the annular fuel rod inlet remains unchanged, the coolant flow distribution ratio in the inner and outer channels of the annular fuel rod will affect the heat transfer process of the annular fuel. The coolant flow distribution in the inner and outer channels of the annular fuel assembly in the core is based on the same coolant flow pressure drop. The coolant flow pressure drop calculation method is shown in formula (5). Formula (5) Where: —Total flow pressure drop in the coolant channel; — fluid pressure drop in the coolant channel; —Friction resistance pressure drop in coolant channel; —Local resistance pressure drop in the coolant channel; 2) Adjust the coolant flow distribution ratio of the inner and outer channels of the annular fuel rod, i.e., the coolant flow distribution coefficient, and return to step 3 to calculate the coolant temperature distribution and the annular fuel rod temperature distribution under the updated coolant mass flow rates of the inner and outer channels of the annular fuel rod until the coolant flow distribution coefficient of the inner and outer channels of the annular fuel rod converges, i.e., the coolant flow pressure drop in the inner and outer channels is the same; 3) Based on the above process, the thermal-hydraulic parameters of the reactor core loaded with annular fuel assemblies are calculated, including the temperature distribution of all annular fuel rods and the coolant temperature distribution in the annular fuel assembly of the entire core.

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