A fuel power calibration method for loop irradiation test

Abstract

The present invention relates to the field of research reactor fuel irradiation technology, and in particular, provides a fuel power calibration method for loop irradiation testing. The method comprises: conducting an off-core hydraulic test and establishing a high-precision CFD model of the fuel loop irradiation device based on the hydraulic test results; calculating the ratio of the gamma heat release rate of each material and the total heat release in the test section to preliminarily determine the nuclear power value of the fuel assembly; correcting the material gamma heat release rate and the fuel assembly nuclear power value based on the heat conduction differential equation and the convection heat transfer equation; repeating the S3 calculation process until the fuel assembly nuclear power value converges to obtain the final theoretical calculated values of the gamma heat release rate of each material and the nuclear power of the fuel assembly; further verifying the calculated results to ultimately obtain the nuclear power of the fuel core, and obtaining the fuel assembly burnup during the irradiation test through time integration. The method aims to solve the technical problem of the deviation between the fuel assembly nuclear power calculated based on thermal measurement data and the actual value in loop irradiation testing.

Description

Technical Field

[0001] The present invention relates to the technical field of research reactor fuel irradiation, and in particular to a fuel power calibration method for loop irradiation testing. Background Art

[0002] A very important step in the design verification phase of fuel elements is to irradiate the fuel elements within the expected fuel life cycle and obtain the necessary test data in a timely manner during or after the irradiation test. Researchers can evaluate the comprehensive performance of the fuel elements in the research reactor and verify the rationality of their structural design, the reliability of the manufacturing process and the feasibility of their application.

[0003] In high-throughput research reactors (HTRs), fuel element irradiation is typically conducted through loop irradiation tests or in-process instrumented irradiation tests. The corresponding device housing the fuel elements is called a loop irradiator or in-process instrumented irradiator. This loop irradiation test device typically performs irradiation tests on small-scale fuel assemblies and can simulate the thermal, hydraulic, and hydrochemical environments of a prototype reactor. The loop irradiator is internally isolated from the reactor coolant. Heat released from the fuel assemblies and structural materials within the device is carried away by the coolant within the irradiation test loop and transferred to the secondary water circuit via a heat exchanger.

[0004] Nuclear power and burnup are key indicators of fuel assembly irradiation testing. Accurately determining these parameters during irradiation testing not only ensures fuel assembly safety but also determines whether the target burnup has been achieved. During the testing process, fuel assembly burnup is typically tracked and calculated using both neutronic calculations and extrapolation based on thermal measurement data.

[0005] The burnup calculation method based on thermal measurement data first uses thermal measurement data from the cooling water within the test loop to determine the fuel assembly's heat release power using the heat balance method. The fuel assembly burnup is then calculated by integrating the heat release power over time. However, the heat release power calculated based on the cooling water inlet and outlet temperatures and flow rates includes the nuclear fission power of the fuel assembly within the device, as well as the gamma heat release power of the nuclear fuel and structural materials. Therefore, the fuel assembly nuclear power calculated based on thermal measurement data deviates from the actual value, and the corresponding burnup value will also be inaccurate. Summary of the Invention

[0006] In view of this, the present invention provides a fuel power calibration method for loop irradiation test, which is used to solve the technical problem that the nuclear power of the fuel assembly calculated based on thermal measurement data in the existing loop irradiation test technology deviates from the actual value.

[0007] The embodiments of the present invention are achieved through the following technical solutions:

[0008] A fuel power calibration method for a loop irradiation test comprises the following steps:

[0009] S1. Conduct ex-pile hydraulic tests, establish a high-precision CFD model of the fuel loop irradiation device based on the hydraulic test results, and analyze the CFD calculation results to determine the coolant flow distribution within the loop irradiation device box;

[0010] S2. Calculate the gamma heat release rate ratio of each material and the total heat release within the test section of the fuel circuit irradiation device. Based on historical operating experience, preliminarily set the gamma heat release rate of the material to obtain the pressure tube heat release P1 and the manifold heat release P2, thereby preliminarily determining the nuclear power value of the fuel assembly.

[0011] S3. Calculate the heat dissipation from the pressure tube to the reactor coolant and the heat transfer process of the coolant inside and outside the box through the box based on the heat conduction differential equation and the convection heat transfer equation, thereby correcting the gamma heat release rate of the material and preliminarily determining the nuclear power value of the fuel assembly;

[0012] S4. Repeat the calculation process of S3 until the gamma heat release rate of the material and the nuclear power value of the fuel assembly converge, thereby obtaining the final theoretical calculated value of the gamma heat release rate of each material and the nuclear power of the fuel assembly;

[0013] S5. Use high-precision analytical calculation methods to correct the theoretical calculated values, and further verify the calculation results through thermal measurement data, so as to finally obtain the nuclear power of the fuel core. The time integral of the nuclear power is used to obtain the burnup of the fuel assembly during the irradiation test.

[0014] Furthermore, in the fuel circuit irradiation device, thermocouples for measuring the coolant temperature are arranged on the outer wall of the upper end of the square box, the component inlet position and the component outlet position.

[0015] Furthermore, the S1 also includes: establishing a CFD model of the test section where the fuel assembly is located and analyzing the CFD calculation results, and comparing the CFD results with the off-core hydraulic test results, so as to obtain a high-precision CFD model of the fuel loop irradiation device.

[0016] Furthermore, the step S2 specifically includes the following steps:

[0017] S21. Obtaining the gamma heat release rate ratio of each material in the fuel loop irradiation device based on the neutronics calculation results;

[0018] S22. Calculate the total heat release in the test section of the fuel circuit irradiation device based on the irradiation test data using the heat balance method;

[0019] S23. Preliminarily set the gamma heat release rate of one of the materials, and obtain the gamma heat release power of the other materials based on the actual mass ratio of each material, to preliminarily obtain the nuclear power value of the fuel assembly;

[0020] Furthermore, the materials include pressure tubes, square boxes, spacers, fuel claddings and fuel cores; and the irradiation test data include coolant flow and thermocouple measurement point temperature.

[0021] Furthermore, in S3, the heat absorbed by the coolant flowing through the fuel assembly area is balanced with the heat released within the device and the heat dissipated by the device to the reactor, that is:

[0022] (1)

[0023] in, m Indicates the coolant mass flow rate; h 1 is the specific enthalpy of the coolant on the outer wall of the upper end of the box, h 2 is the specific enthalpy of the coolant at the fuel assembly outlet, P 1 is the heat release of the pressure pipe, P 2 is the heat release of the shunt pipe, P s Release heat to the fuel assembly, Q c is the heat dissipation capacity, Q r is the amount of heat dissipated by radiation;

[0024] Energy conservation exists in the region inside and outside the shunt pipe, namely:

[0025] (2)

[0026] (3)

[0027] in, h 0 is the specific enthalpy of the coolant at the fuel assembly inlet, P L The cooling water in the shunt pipe releases heat to the cooling water outside the shunt pipe;

[0028] The inner and outer walls of the shunt pipe are used for cooling water convection. The shunt pipe itself is a radial heat conductor with an internal heat source. Based on the heat conduction differential equation and the convection heat transfer equation, we have:

[0029] (4)

[0030] in, T f1 is the qualitative temperature of the coolant between the shunt pipe and the pressure pipe, T f2 is the qualitative temperature of the coolant in the shunt pipe; r 1 and r2 are the inner and outer wall diameters of the diverter pipe respectively; S 1 and S 2 are the inner and outer wall areas of the diverter pipe respectively; a 1 and a 2 are the convection heat transfer coefficients of the inner and outer flow channels of the diverter pipe, which can be obtained from the heat transfer relationship; λ 1 is the thermal conductivity of the shunt pipe; is the volume heat release rate of the shunt pipe; l is the height of the area where the fuel assembly is located.

[0031] Furthermore, the qualitative temperature of the coolant between the shunt pipe and the pressure pipe T f1 Calculated using the following formula:

[0032] T f1 =( T 1+ T 0) / 2(5);

[0033] Qualitative temperature of coolant in the shunt pipe T f2 Calculated by the following formula:

[0034] T f2 =( T 0+ T 2) / 2(6)

[0035] in, T 0 is the fuel assembly inlet temperature, T 1 is the coolant temperature of the outer wall of the upper end of the box, T 2 is the fuel assembly outlet temperature.

[0036] Furthermore, in said S4, the deviation of the nuclear power value of the fuel assembly before and after correction is compared. When the deviation is greater than the convergence range, the gamma heat release rate of the initially set material needs to be corrected, and the iterative cycle is repeated until the deviation of the nuclear power value of the fuel assembly before and after correction is within the convergence range.

[0037] Furthermore, the S5 includes the following sub-steps:

[0038] S51. Use the gamma heat release rate of the material and the nuclear power value of the fuel assembly as the heat source input of the high-precision CFD model, and use the thermal measurement data as the inlet boundary conditions of the high-precision CFD model to perform CFD analysis and calculation;

[0039] S52. Compare the CFD calculation results with the actual irradiation test temperature measurements. Based on the comparison results, further correct the gamma heat release rate of each material and the nuclear power of the fuel assembly according to the pressure tube heat dissipation obtained by the high-precision CFD model;

[0040] S53, repeating step S51 again using the updated heat source to perform CFD analysis and calculation;

[0041] S54, repeat the above steps, iterating until the calculated temperature value matches the measured temperature value, and obtaining the final material heat release rate and the nuclear power of the fuel core;

[0042] S55. Regularly update the gamma heat release rate ratio of each material, re-iterate the material gamma heat release rate and the fuel assembly nuclear power, and obtain the fuel assembly burnup in the irradiation test through the time integral of the nuclear power.

[0043] Furthermore, the thermal measurement data in S51 refers to the temperature measurement value of the outer wall of the upper end of the square box and the coolant flow rate.

[0044] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:

[0045] (1) Based on the thermal balance method, supplemented by neutronic calculation results, and making full use of thermal measurement data, a more accurate real-time calculation of the fuel nuclear power in the loop irradiation test can be achieved based on the thermal measurement data from a thermal perspective. This can effectively eliminate the uncertainty of factors such as material gamma heat release and heat loss on the nuclear power calculation, realize real-time calculation of the nuclear power of the fuel assembly, and thus support the determination of fuel burnup during the irradiation test;

[0046] (2) Based on theoretical calculations, the heat transfer process in the fuel loop irradiation device is effectively analyzed to identify the heat transfer from the coolant inside the box to the coolant outside the box and the heat dissipation from the device to the research reactor coolant through the pressure tube, thereby reducing the deviation between the nuclear power of the fuel assembly calculated based on thermal measurement data and the actual value;

[0047] (3) Using the theoretically calculated material gamma heat release and fuel nuclear power as heat source inputs for the CFD calculation model can further reduce the number of iterations in the CFD simulation process and accelerate the convergence speed;

[0048] (4) Taking the typical material heat release rate as the initial value of the iteration, through the dual iteration of theoretical calculation based on the heat conduction differential equation and high-precision simulation calculation based on CFD, the influence of factors such as material heat release and device heat loss on the uncertainty of nuclear power calculation can be effectively corrected. At the same time, the number of iterations can be greatly reduced, the analysis and calculation time can be saved, and the iterative efficiency of nuclear power calculation can be effectively improved.

[0049] (5) A high-precision CFD model of the fuel circuit irradiation device is established through CFD. High-precision simulation calculations are carried out using thermal measurement data consistent with theoretical calculations. The reliability of the CFD calculation results is verified using the temperature test values of thermal measurements, thereby effectively ensuring the accuracy of the calculation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0051] Figure 1 It is a schematic diagram of the present invention;

[0052] Figure 2 It is a schematic structural diagram of the loop irradiation device of the present invention.

[0053] Figure 3 Schematic diagram of the shunt pipe assembly;

[0054] Figure 4 This is a diagram of the first thermocouple arrangement in the fuel assembly area;

[0055] Figure 5 This is a diagram of the second thermocouple arrangement in the fuel assembly area;

[0056] Figure 6 This is a schematic diagram of the heat transfer process in the fuel assembly area of the loop irradiation test device;

[0057] In the figure, 1-insulation pipe assembly; 2-pressure pipe assembly; 3-diversion pipe assembly; 4-transition pipe assembly; 5-lifting head assembly; 6-connecting pipe; 7-inner diversion pipe; 8-outer diversion pipe; 9-spring; 10-spring base; 11-square box; 12-square and round joint; 13-pressure pipe; 14-insulation pipe; 1#~8# are thermocouples. DETAILED DESCRIPTION

[0058] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0059] like Figure 2As shown, the loop irradiation device of the present invention includes an insulation tube assembly 1, a pressure tube assembly 2, a manifold assembly 3, and a transition tube assembly 4. The insulation tube assembly 1 is located on the outer layer of the pressure tube assembly 2, with its upper flange connected to the large reactor flat top cover and its lower joint inserted into the grid plate. The lower flange end face of the transition tube assembly 4 is connected to the insulation tube flange, and its upper flange end face is connected to the middle flange of the pressure tube assembly 2. Nitrogen is filled between the insulation tube 14 and the pressure tube 13 to detect whether the pressure tube 13 is leaking. The outside of the insulation tube 14 is filled with reactor coolant, and there is a nitrogen layer between the insulation tube 14 and the pressure tube 13. Therefore, a small amount of heat released within the device will also be lost to the reactor coolant. The manifold assembly 3 is located inside the pressure tube assembly 2, and the fuel assembly is placed in the square box of the manifold assembly 3. The fuel assembly is compressed by the bracket of the lower head assembly of the pressure tube assembly 2 and the spring base 10 of the manifold assembly 3.

[0060] like Figure 3 As shown, the manifold assembly 3 primarily consists of a lifting head assembly 5, a connecting pipe 6, an inner manifold 7, an outer manifold 8, a square-round joint 12, a square box 11, a spring 9, and a spring base 10. The upper portion of the manifold connects the lifting head assembly 5, the inner manifold 7, and the outer manifold 8 via the connecting pipe 6. The lower portion connects the inner manifold 7, the outer manifold 8, and the square box 11 via the square-round joint 12. The fuel assembly is placed within the square box 11 of the manifold assembly 3 and is held in place by the bracket of the lower head assembly of the pressure tube assembly 2 and the spring base 10 of the manifold assembly 3.

[0061] like Figure 4 and Figure 5 As shown, the fuel loop irradiation device arranges 8 thermocouples in the area near the fuel assembly, with the 1# thermocouple located on the upper outer wall of the square box 11; the 3#, 4# and 6# thermocouples are located at the inlet of the assembly, with the 3# and 4# thermocouples located on the positive side and the 6# thermocouple located on the negative side; the 2# and 5# thermocouples are located at the outlet of the assembly, with the 2# thermocouple located on the positive side and the 5# thermocouple located on the negative side.

[0062] like Figure 1 and Figure 6 As shown, a fuel power calibration method for loop irradiation test includes the following steps:

[0063] S1. Based on the structural design of the fuel loop irradiation device, complete the device processing and assembly and conduct off-pillar cold hydraulic tests. Build a CFD model of the test section where the fuel assembly is located and analyze the calculation results. Compare the CFD results with the off-pillar hydraulic test results to obtain a high-precision CFD model for flow and heat transfer simulation in subsequent test sections, thereby obtaining the flow distribution of the coolant between the square box 11 and the annular slit between the lower tube seat and the square box 11.

[0064] S2. Based on neutronic calculations, the gamma heat release ratio of each material in the fuel circuit irradiation device (including the pressure tube 13, box 11, spacers, fuel cladding, and fuel core) is calculated, assuming that this ratio remains constant over a given irradiation period. Based on irradiation test data such as coolant flow rate and thermocouple temperature, the total heat release within the test section of the fuel circuit irradiation device can be calculated using the heat balance method. Based on historical operating experience, the gamma heat release ratio of a specific structural material is initially assumed, and the gamma heat release ratios of other materials are calculated proportionally. Based on the actual mass of each material, the gamma heat release power can be calculated, and thus the nuclear power value of the fuel assembly can be preliminarily determined.

[0065] S3. Based on the coolant flow distribution scheme within the box, using the heat conduction differential equation and the convection heat transfer equation, theoretical calculations are performed for the heat dissipation from the pressure tube 13 to the reactor coolant through the nitrogen layer, the flow and heat transfer of the coolant through the flow channel between the pressure tube 13 and the box 11, the flow and heat transfer of the coolant through the fuel assembly within the box 11, and the heat transfer of the coolant inside and outside the box through the box 11. The heat transfer between unventilated areas is calculated, including the heat dissipation from the pressure tube 13 to the reactor coolant and the heat transfer of the coolant inside and outside the box through the box 11. This is used to correct the gamma heat release rate of the material and the preliminary fuel assembly nuclear power determined by the heat balance method. Specifically, this can be implemented according to the following process:

[0066] The heat absorbed by the coolant flowing through the fuel assembly area is balanced with the heat released within the device and the heat dissipated from the device to the reactor, that is:

[0067] (1)

[0068] in, m is the coolant mass flow rate, which can be measured in the circuit; h 1 and h 2 are the specific enthalpies of the coolant at the inlet and outlet of the active zone, and their temperatures can be measured by thermocouples.

[0069] Energy conservation also exists in the areas inside and outside the shunt pipe, that is:

[0070] (2)

[0071] (3)

[0072] Equations (1), (2) and (3) can be derived from two of them to form the third one.

[0073] Qualitative temperature of coolant between shunt pipe and pressure pipe 13 T f1 Calculated using the following formula:

[0074] Tf1 =( T 1+ T 0) / 2(5)

[0075] Qualitative temperature of coolant in the shunt pipe T f2 Calculated by the following formula:

[0076] T f2 =( T 0+ T 2) / 2(6)

[0077] in, T 0 is the fuel assembly inlet temperature, T 1 is the coolant temperature of the outer wall of the upper end of the box, T 2 is the fuel assembly outlet temperature.

[0078] The inner and outer walls of the shunt pipe are for cooling water convection heat transfer, and the shunt pipe itself is for radial heat conduction with an internal heat source. Based on the heat conduction differential equation and the convection heat transfer equation, we have:

[0079] (4)

[0080] in, r 1 and r 2 are the inner and outer wall diameters of the diverter pipe respectively; S 1 and S 2 are the inner and outer wall areas of the diverter pipe respectively; a 1 and a 2 are the convection heat transfer coefficients of the inner and outer flow channels of the diverter pipe, which can be obtained from the heat transfer relationship; λ 1 is the thermal conductivity of the shunt pipe; is the volume heat release rate of the shunt pipe, which is related to the heat release rate of the shunt pipe. P 2 are closely related.

[0081] Initially set the material heat release rate to get the pressure pipe heat release P 1 and shunt pipe heat release P 2, thus improving the heat dissipation Q c and radiative heat dissipation Q r Solve it and then get formula (1) P s , thus solving the nuclear heat release of the fuel assembly; through (2) and P s , can be P L Solve; through (4), P L as well as P sThe heat release rate of the diverter tube volume Solve it and get the heat release of the shunt pipe P 2. At the same time, correct the heat release of the pressure pipe P 1.

[0082] S4. Repeat the calculation process of S3 until the gamma heat release rate of the material and the nuclear power value of the fuel assembly converge, thereby obtaining the final theoretical calculated value of the gamma heat release rate of each material and the nuclear power of the fuel assembly;

[0083] Specifically, the deviation of the nuclear power value of the fuel assembly before and after correction is compared. When the deviation is greater than the convergence range, the gamma heat release rate of the initially set material needs to be corrected. The iteration cycle is repeated until the deviation of the nuclear power value of the fuel assembly before and after correction is within the convergence range. Here, the convergence range is 10 -4 .

[0084] S5. Use high-precision analytical calculation methods to correct the theoretical calculated values, and further verify the calculated results through thermal measurement data, so as to finally obtain the nuclear power of the fuel core. The time integral of the nuclear power is used to obtain the burnup of the fuel assembly during the irradiation test.

[0085] Specifically, in this example, a high-precision analytical calculation model for the fuel loop irradiation device test section was established based on CFD. The heat release rates of structural materials and the nuclear power of the fuel assemblies served as the heat source inputs for the CFD calculation model, while the temperature measurements of the No. 1 thermocouple and the coolant flow rate served as the inlet boundary conditions. The CFD calculation results were compared with actual irradiation test temperature measurements, such as the assembly inlet and outlet temperatures. Based on the difference between the two and the heat dissipation of the pressure tubes obtained through CFD, the gamma heat release rates of each structural material and the nuclear power of the fuel assembly were further corrected. The CFD calculation was then repeated using the updated heat source. This process was repeated until the calculated temperature values were in good agreement with the measured values, resulting in the final structural material heat release rates and fuel assembly nuclear power.

[0086] The integral of the nuclear power of the fuel assembly over time is the burnup. For long-period loop irradiation tests, the gamma heat release rate ratio of each material needs to be updated at regular intervals, and the material heat release rate and the nuclear power of the fuel assembly need to be re-iterated according to the above power calibration process. The corresponding fuel burnup is accumulated after segmented integration.

[0087] Specifically, in this embodiment, the neutron calculation results are updated when the core loading changes.

[0088] While the basic concepts have been described above, it will be apparent to those skilled in the art that the detailed disclosure is merely illustrative and does not limit this specification. Although not explicitly stated herein, various modifications, improvements, and revisions to this specification may be made by those skilled in the art. Such modifications, improvements, and revisions are suggested in this specification and remain within the spirit and scope of the exemplary embodiments of this specification.

[0089] Similarly, it should be noted that, in order to simplify the presentation of this specification and thus facilitate understanding of one or more embodiments of the invention, the foregoing descriptions of the embodiments of this specification sometimes combine multiple features into a single embodiment, figure, or description thereof. However, this disclosure method does not imply that the subject matter of this specification requires more features than those recited in the claims. In fact, an embodiment may have fewer features than all of the features of a single disclosed embodiment.

[0090] Finally, it should be understood that the embodiments described in this specification are intended only to illustrate the principles of the embodiments of this specification. Other variations may also fall within the scope of this specification. Therefore, by way of example and not limitation, alternative configurations of the embodiments of this specification may be considered consistent with the teachings of this specification. Accordingly, the embodiments of this specification are not limited to the embodiments explicitly described and illustrated in this specification.

Claims

1. A fuel power calibration method for loop irradiation test, characterized in that: The following steps are involved: S1. Conduct ex-pile hydraulic tests, establish a high-precision CFD model of the fuel loop irradiation device based on the hydraulic test results, and analyze the CFD calculation results to determine the coolant flow distribution within the loop irradiation device box; S2. Calculate the gamma heat release rate ratio of each material and the total heat release in the test section of the fuel circuit irradiation device. Based on historical operating experience, the gamma heat release rate of the material is initially set to obtain the pressure pipe heat release rate. P 1 and shunt pipe heat release P 2. Then preliminarily determine the nuclear power value of the fuel assembly; S3. Calculate the heat dissipation from the pressure tube to the reactor coolant and the heat transfer process of the coolant inside and outside the box through the box based on the heat conduction differential equation and the convection heat transfer equation, thereby correcting the gamma heat release rate of the material and preliminarily determining the nuclear power value of the fuel assembly; S4. Repeat the calculation process of S3 until the gamma heat release rate of the material and the nuclear power value of the fuel assembly converge, thereby obtaining the final theoretical calculated value of the gamma heat release rate of each material and the nuclear power of the fuel assembly; S5. Use high-precision analytical calculation methods to correct the theoretical calculated values, and further verify the calculation results through thermal measurement data, so as to finally obtain the nuclear power of the fuel core. The time integral of the nuclear power is used to obtain the burnup of the fuel assembly during the irradiation test.

2. A fuel power calibration method for loop irradiation test according to claim 1, characterized in that: In the fuel circuit irradiation device, thermocouples for measuring the coolant temperature are arranged on the outer wall of the upper end of the square box, the component inlet position and the component outlet position.

3. A fuel power calibration method for loop irradiation test according to claim 1, characterized in that: Said S1 also includes: establishing a CFD model of the test section where the fuel assembly is located and analyzing the CFD calculation results, and comparing the CFD results with the results of the off-core hydraulic test, so as to obtain a high-precision CFD model of the fuel loop irradiation device.

4. A fuel power calibration method for loop irradiation test according to claim 1, characterized in that: The S2 specifically includes the following steps: S21. Obtaining the gamma heat release rate ratio of each material in the fuel loop irradiation device based on the neutronics calculation results; S22. Calculate the total heat release in the test section of the fuel circuit irradiation device based on the irradiation test data using the heat balance method; S23. Preliminarily set the gamma heat release rate of one of the materials, and obtain the gamma heat release power of the other materials based on the actual mass ratio of each material, and preliminarily obtain the nuclear power value of the fuel assembly.

5. A fuel power calibration method for loop irradiation test according to claim 4, characterized in that: The materials include pressure tubes, square boxes, spacers, fuel claddings and fuel cores; the irradiation test data include coolant flow and thermocouple measuring point temperature.

6. A fuel power calibration method for loop irradiation test according to claim 1, characterized in that: In S3, the heat absorbed by the coolant flowing through the fuel assembly area is balanced with the heat released in the device and the heat dissipated by the device to the reactor, that is: （1） in, m Indicates the coolant mass flow rate; h 1 is the specific enthalpy of the coolant on the outer wall of the upper end of the box, h 2 is the specific enthalpy of the coolant at the fuel assembly outlet, P 1 is the heat release of the pressure pipe, P 2 is the heat release of the shunt pipe, P s Release heat to the fuel assembly, Q c is the heat dissipation capacity, Q r is the amount of heat dissipated by radiation; Energy conservation exists in the region inside and outside the shunt pipe, namely: （2） （3） in, h 0 is the specific enthalpy of the coolant at the fuel assembly inlet, P L The cooling water in the shunt pipe releases heat to the cooling water outside the shunt pipe; The inner and outer walls of the shunt pipe are used for cooling water convection. The shunt pipe itself is a radial heat conductor with an internal heat source. Based on the heat conduction differential equation and the convection heat transfer equation, we have: （4） in, T f1 is the qualitative temperature of the coolant between the shunt pipe and the pressure pipe, T f2 is the qualitative temperature of the coolant in the shunt pipe; r 1 and r 2 are the inner and outer wall diameters of the diverter pipe respectively; S 1 and S 2 are the inner and outer wall areas of the diverter pipe respectively; a 1 and a 2 are the convection heat transfer coefficients of the inner and outer flow channels of the diverter pipe, which can be obtained from the heat transfer relationship; λ 1 is the thermal conductivity of the shunt pipe; is the volume heat release rate of the shunt pipe; l is the height of the area where the fuel assembly is located.

7. A fuel power calibration method for loop irradiation test according to claim 6, characterized in that: Qualitative temperature of coolant between shunt pipe and pressure pipe T f1 Calculated using the following formula: T f1 =( T 1+ T 0) / 2（5）； Qualitative temperature of coolant in the shunt pipe T f2 Calculated by the following formula: T f2 =( T 0+ T 2) / 2（6） in, T 0 is the fuel assembly inlet temperature, T 1 is the coolant temperature of the outer wall of the upper end of the box, T 2 is the fuel assembly outlet temperature.

8. A fuel power calibration method for loop irradiation test according to claim 1, characterized in that: In the above S4, the deviation of the nuclear power values of the fuel assembly before and after correction is compared. When the deviation is greater than the convergence range, the gamma heat release rate of the initially set material needs to be corrected, and the process is iterated until the deviation of the nuclear power values of the fuel assembly before and after correction is within the convergence range.

9. A fuel power calibration method for loop irradiation test according to claim 1, characterized in that: The S5 comprises the following sub-steps: S51. Use the gamma heat release rate of the material and the nuclear power value of the fuel assembly as the heat source input of the high-precision CFD model, and use the thermal measurement data as the inlet boundary conditions of the high-precision CFD model to perform CFD analysis and calculation; S52. Compare the CFD calculation results with the actual irradiation test temperature measurements. Based on the comparison results, further correct the gamma heat release rate of each material and the nuclear power of the fuel assembly according to the pressure tube heat dissipation obtained by the high-precision CFD model; S53, repeating step S51 again using the updated heat source to perform CFD analysis and calculation; S54, repeat the above steps, iterating until the calculated temperature value matches the measured temperature value, and obtaining the final material heat release rate and the nuclear power of the fuel core; S55. Regularly update the gamma heat release rate ratio of each material, re-iterate the material gamma heat release rate and the fuel assembly nuclear power, and obtain the fuel assembly burnup in the irradiation test through the time integral of the nuclear power.

10. A fuel power calibration method for loop irradiation test according to claim 9, characterized in that: The thermal measurement data in S51 refers to the temperature measurement value of the outer wall of the upper end of the square box and the coolant flow rate.

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