Fuel loading structure of reactor core balance cycle, fuel management method and system

Abstract

The invention discloses a fuel loading structure and a fuel management method and system for a reactor core balance cycle, the fuel loading structure comprises N1 first new fuel assemblies with the enrichment degree of 4.95% and N2 second new fuel assemblies with the enrichment degree of 4.45%, and N1 and N2 are related to the cycle length of the reactor core balance cycle; in the radial direction of the reactor core, the N1 first new fuel assemblies and the N2 second new fuel assemblies are arranged on the secondary outer ring and the interior of the reactor core, and the N1 first new fuel assemblies are arranged on the periphery of the N2 second new fuel assemblies; the N1 first new fuel assemblies are respectively in axial symmetry relative to the two symmetric axes of the reactor core and are in central symmetry relative to the central point of the reactor core, and the N2 second new fuel assemblies are respectively in axial symmetry relative to the two symmetric axes of the reactor core and are in central symmetry relative to the central point of the reactor core. According to the technical scheme, the long circulation requirement from the Spring Festival to the next National Day can be met.

Description

Technical Field

[0001] The present application relates to the field of nuclear power technology, and in particular to a fuel loading structure, a fuel management method and a system for a core balance cycle. Background Art

[0002] At present, nuclear power plants generally adopt an annual refueling mode for the first cycle, and quickly transition to 18-month refueling from the second cycle. The second and third cycles are transition cycles, and the fourth cycle begins to enter the balance cycle, and the core refueling follows the "in-out" mode. Typical balance cycles are divided into long cycles and short cycles. For example, the core fuel management plan of a nuclear power plant adopts a long balance cycle of 509 days and a short balance cycle of 469 days. In addition, it also includes four flexibility cycles, of which the longest is 530 days and the shortest is 445 days.

[0003] Considering the power grid environment of nuclear power plants and the need to schedule overhauls during the low-load periods of the Spring Festival and National Day, the longest flexibility cycle is only 530 days, while the period from the Spring Festival of the current year to the National Day of the next year is generally about 560-580 days. Therefore, the shortcomings of the current fuel management scheme are that the fuel management strategy adopted by the unit cannot meet the needs of the overhaul window, and either long-term extended operation is forced to be adopted, or overhaul is forced to be carried out in advance during the power supply period, affecting the power supply and unit operation safety. Summary of the invention

[0004] The technical problem to be solved by the present application is to provide a fuel loading structure, a fuel management method and a system for a core balancing cycle in view of the technical defect in the prior art that the balancing cycle length in the existing fuel management strategy affects the power supply and the safety of unit operation.

[0005] The technical solution adopted by the present application to solve the technical problem is: construct a fuel loading structure for a core balance cycle, including N1 first new fuel assemblies with an enrichment degree of 4.95% and N2 second new fuel assemblies with an enrichment degree of 4.45%, wherein N1 and N2 are natural numbers respectively and are related to the cycle length of the core balance cycle, and the cycle length includes more than 550 days and 460-470 days;

[0006] In the radial direction of the core, N1 of the first new fuel assemblies and N2 of the second new fuel assemblies are arranged in the sub-outer circle and the interior of the core, and N1 of the first new fuel assemblies are arranged around the N2 of the second new fuel assemblies; the N1 of the first new fuel assemblies are axially symmetric with respect to the two symmetry axes of the core and are centrally symmetric with respect to the center point of the core, and the N2 of the second new fuel assemblies are axially symmetric with respect to the two symmetry axes of the core and are centrally symmetric with respect to the center point of the core.

[0007] Optionally, when the core is a 157 core and the cycle length is more than 550 days, N1 is 40, N2 is 32, and in a core coordinate system with an abscissa of AR and an ordinate of 1-15,

[0008] The loading positions of the 40 first new fuel assemblies are: H14, G14, J14, G13, F13, E13, J13, K13, L13, D12, M12, C11, N11, C10, N10, B9, C9, P9, N9, B8, P8, B7, C7, P7, N7, C6, N6, C5, N5, D4, M4, G3, F3, E3, J3, K3, L3, H2, G2, J2;

[0009] The loading positions of the 32 second new fuel assemblies are: F12, K12, G11, E11, J11, L11, H10, F10, D10, K10, M10, G9, E9, J9, L9, F8, K8, G7, E7, J7, L7, H6, F6, D6, K6, M6, G5, E5, J5, L5, F4, K4.

[0010] Optionally, among the 40 first new fuel assemblies, the first new fuel assemblies at H14, G13, F13, J13, K13, C10, N10, C9, N9, B8, P8, C7, N7, C6, N6, G3, F3, J3, K3, and H2 each include 20 gadolinium rods and 244 uranium rods;

[0011] The first new fuel assemblies at G14, J14, E13, L13, C11, N11, B9, P9, B7, P7, C5, N5, E3, L3, G2, and J2 each include 8 gadolinium rods and 256 uranium rods;

[0012] The first new fuel assemblies at D12, M12, D4, and M4 each include 16 gadolinium rods and 248 uranium rods.

[0013] Optionally, among the 32 second new fuel assemblies, the second new fuel assemblies at G11, E11, J11, L11, G9, E9, J9, L9, G7, E7, J7, L7, G5, E5, J5, and L5 each include 24 gadolinium rods and 240 uranium rods;

[0014] The second new fuel assemblies at F12, K12, H10, F10, D10, K10, M10, F8, K8, H6, F6, D6, K6, M6, F4, and K4 each include 20 gadolinium rods and 244 uranium rods.

[0015] Optionally, when the core is 157 cores and the cycle length is 460-470 days, N1 is 32, N2 is 32, and in the core coordinate system with the horizontal axis being AR and the vertical axis being 1-15,

[0016] The loading positions of the 32 first new fuel assemblies are: H14, G14, J14, E13, F13, L13, K13, D12, M12, C11, N11, C10, N10, B9, P9, B8, P8, B7, P7, C6, N6, C5, N5, D4, M4, E3, F3, L3, K3, H2, G2, J2;

[0017] The loading positions of the 32 second new fuel assemblies are: G13, J13, H12, G11, E11, J11, L11, F10, K10, G9, E9, C9, J9, L9, N9, D8, M8, G7, E7, C7, J7, L7, N7, F6, K6, G5, E5, J5, L5, H4, G3, J3.

[0018] Optionally, among the 32 first new fuel assemblies, the first new fuel assemblies at H14, G14, J14, E13, L13, D12, M12, C11, N11, B9, P9, B8, P8, B7, P7, C5, N5, D4, M4, E3, L3, H2, G2, and J2 each include 8 gadolinium rods and 256 uranium rods;

[0019] The first new fuel assemblies at F13, K13, C10, N10, C6, N6, F3, and K3 each include 16 gadolinium rods and 248 uranium rods.

[0020] Optionally, 32 second new fuel assemblies each include 16 gadolinium rods and 248 uranium rods.

[0021] The present invention also provides a fuel management method for a core balance cycle, the fuel management method comprising:

[0022] Step S10, determining the cycle length corresponding to each overhaul according to the overhaul plan information of the nuclear power unit;

[0023] Step S20, for each overhaul, determine the number N1 and loading positions of the first new fuel assemblies with an enrichment of 4.95%, and the number N2 and loading positions of the second new fuel assemblies with an enrichment of 4.45% according to the determined cycle length, so as to obtain the fuel loading structure of the overhaul, wherein N1 and N2 are natural numbers, and are related to the cycle length of the core balance cycle, and the cycle length includes more than 550 days and 460-470 days; in the radial direction of the core, N1 of the first new fuel assemblies and N2 of the second new fuel assemblies are arranged in the sub-outer circle and the inner part of the core, and the N1 of the first new fuel assemblies are arranged around the N2 of the second new fuel assemblies; the N1 of the first new fuel assemblies are respectively axially symmetric with respect to the two symmetry axes of the core, and are centrosymmetric with respect to the center point of the core, and the N2 of the second new fuel assemblies are respectively axially symmetric with respect to the two symmetry axes of the core, and are centrosymmetric with respect to the center point of the core;

[0024] Step S30, respectively simulate and analyze the fuel loading structure of each overhaul, and respectively determine whether the corresponding preset conditions are met, and if so, execute step S40;

[0025] Step S40, taking the obtained fuel loading structure as the final fuel loading structure, and performing fuel replacement of the fuel assembly according to the corresponding final fuel loading structure when performing the corresponding overhaul.

[0026] Optionally, the step S20 further includes:

[0027] The number of gadolinium rods in each of the first new fuel assemblies and each of the second new fuel assemblies is determined.

[0028] The present invention also constructs a fuel management system for a core balancing cycle, comprising a processor and a memory storing a computer program, wherein the processor implements the steps of the fuel management method for a core balancing cycle described above when executing the computer program.

[0029] In the technical solution of the present application, the fuel loading structure of the core balance cycle is designed by using two enrichment fuel assemblies of 4.45% and 4.95%, which can make the cycle length of the long cycle greater than 550 days and the cycle length of the short cycle 460-470 days, breaking through the upper limit of the original cycle length, so as to match the long cycle demand from the Spring Festival to the National Day of the next year (generally 560-580 days), avoiding being forced to adopt long-term extended operation or forced to overhaul in advance during the power protection period, while ensuring power supply and unit safety. Moreover, by introducing 4.95% enrichment fuel assemblies, compared with the current single 4.45% enrichment fuel loading scheme, the number of new fuel assemblies entering the stack can be reduced, and the unloading fuel consumption can be increased, thereby improving the economy of the nuclear power unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0031] Figure 1 It is a partial structural schematic diagram of Embodiment 1 of the fuel loading structure of the core balance cycle of the present invention;

[0032] Figure 2 It is a partial structural schematic diagram of Embodiment 2 of the fuel loading structure of the core balance cycle of the present invention;

[0033] Figure 3 It is a flow chart of Example 1 of the fuel management method for the core balance cycle of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0035] The present invention constructs a fuel loading structure for a core balance cycle, which includes an old fuel assembly and N1 first new fuel assemblies with an enrichment of 4.95%, and N2 second new fuel assemblies with an enrichment of 4.45%, wherein N1 and N2 are natural numbers, and are related to the cycle length of the core balance cycle, and the cycle length includes more than 550 days and 460-470 days. In the radial direction of the core, N1 first new fuel assemblies and N2 second new fuel assemblies are arranged in the secondary outer ring and the inner part of the core, the old fuel assembly is arranged in the outermost ring of the core, and N1 first new fuel assemblies are arranged on the periphery of N2 second new fuel assemblies, so that neutron leakage can be minimized. The N1 first new fuel assemblies are respectively axially symmetrical with respect to the two symmetry axes of the core, and are centrosymmetric with respect to the center point of the core, and the N2 second new fuel assemblies are respectively axially symmetrical with respect to the two symmetry axes of the core, and are centrosymmetric with respect to the center point of the core. It should be understood that the layout of the fuel assemblies in the core should also meet the following principle: new fuel assemblies and old fuel assemblies cross-penetrate each other.

[0036] In the technical solution of this embodiment, the fuel loading structure of the core balance cycle is designed by using two enrichment fuel assemblies of 4.45% and 4.95%, which can make the cycle length of the long cycle greater than 550 days and the cycle length of the short cycle between 460-470 days, breaking through the upper limit of the original cycle length, so as to match the long cycle demand during the Spring Festival to the National Day of the next year, avoiding being forced to adopt long-term extended operation or forced to overhaul in advance during the power protection period, while ensuring power supply and unit safety. Moreover, by introducing a 4.95% enrichment fuel assembly, compared with the current single 4.45% enrichment fuel loading scheme, the number of new fuel assemblies entering the stack can be reduced, and the unloading fuel consumption can be increased, thereby improving the economy of the nuclear power unit.

[0037] The following will be combined Figure 1 , Figure 2 The loading structure of the 157 core when the balance cycle is more than 550 days and 460-470 days respectively. Figure 1 , Figure 2 First of all, in the 157 core, the abscissa of the core coordinate system is AR, and the ordinate is 1-15, where H8 is the center point of the core, and the Hth column and the 8th row are the two symmetry axes of the core. It should be understood that since the N1 first new fuel assemblies are respectively axially symmetric with respect to the two symmetry axes of the core and centrosymmetric with respect to the center point of the core, and the N2 second new fuel assemblies are respectively axially symmetric with respect to the two symmetry axes of the core and centrosymmetric with respect to the center point of the core, therefore, Figure 1 , Figure 2 Only the loading structure of 1 / 4 of the core is shown. Figure 1 , 2 In the figure, "NEW" in the fuel assembly indicates that the fuel assembly is a new fuel assembly, and the fuel assembly without the mark "NEW" indicates an old fuel assembly, and the data in the center of the old fuel assembly indicates the reactivity, and the data in the four corners indicates the burnup at the corresponding position. It should be understood that the reactivity and burnup data are only for illustration and will change during the actual core loading design process. In addition, the beige fuel assembly (e.g., fuel assembly T11), the purple fuel assembly (e.g., fuel assembly T12), and the gray fuel assembly (e.g., fuel assembly T13) are the first new fuel assembly (4.95% enrichment), respectively; the red fuel assembly (e.g., fuel assembly T21), the orange fuel assembly (e.g., fuel assembly T22), and the green fuel assembly (e.g., fuel assembly T23) are the second new fuel assembly (4.45% enrichment).

[0038] In addition, the first new fuel assembly and the second new fuel assembly can use 8% (by weight) of gadolinium burnable poison. The burnable poison gadolinium is loaded into the alloy cladding in the form of UO2-Gd2O3 mixed oxide pellets to form a burnable poison rod (referred to as gadolinium rod). 235 The enrichment degree is 2.5%. Generally, a fuel assembly includes 264 rods, of which some (e.g., 8, 16, 20, 24) are gadolinium rods and the rest are uranium rods. Fuel assemblies can be classified according to the number of gadolinium rods in the fuel assembly. Specifically, the first new fuel assembly is divided into three types: the first new fuel assembly with 20 gadolinium rods (e.g., fuel assembly T11), the first new fuel assembly with 8 gadolinium rods (e.g., fuel assembly T12), and the first new fuel assembly with 16 gadolinium rods (e.g., fuel assembly T13); the second new fuel assembly is divided into three types: the second new fuel assembly with 24 gadolinium rods (e.g., fuel assembly T21), the second new fuel assembly with 20 gadolinium rods (e.g., fuel assembly T22), and the second new fuel assembly with 16 gadolinium rods (e.g., fuel assembly T23).

[0039] exist Figure 1 In the embodiment shown, the core is 157 cores, the total number of new fuel assemblies is 72, of which the number N1 of the first new fuel assemblies with an enrichment of 4.95% is 40, and the number N2 of the second new fuel assemblies with an enrichment of 4.45% is 32, and the corresponding cycle length is more than 550 days. In addition, regarding the 85 old fuel assemblies, the number of old fuel assemblies with an enrichment of 4.45% is 36, and the number of old fuel assemblies with an enrichment of 4.95% is 49. At this time, the core composition is as shown in Table 1, wherein N-2 represents the fuel assemblies unloaded in the first two cycles of the current cycle, and the short cycle represents the fuel assemblies unloaded in the previous cycle.

[0040]

[0041] Table 1

[0042] Combination Figure 1As shown in Table 1, the loading positions of the 40 first new fuel assemblies are: H14, G14, J14, G13, F13, E13, J13, K13, L13, D12, M12, C11, N11, C10, N10, B9, C9, P9, N9, B8, P8, B7, C7, P7, N7, C6, N6, C5, N5, D4, M4, G3, F3, E3, J3 , K3, L3, H2, G2, J2. The loading positions of the 32 second new fuel assemblies are: F12, K12, G11, E11, J11, L11, H10, F10, D10, K10, M10, G9, E9, J9, L9, F8, K8, G7, E7, J7, L7, H6, F6, D6, K6, M6, G5, E5, J5, L5, F4, K4. Such a loading structure can not only make the cycle length reach more than 550 days, but also meet the power conditions and safety conditions of the core design. In addition, since the new fuel assemblies are arranged in the secondary outer ring and the inner part, and the old fuel assemblies are arranged in the outer ring, the neutron leakage can also be minimized.

[0043] Further integration Figure 1 Among the 40 first new fuel assemblies, the first new fuel assemblies at H14, G13, F13, J13, K13, C10, N10, C9, N9, B8, P8, C7, N7, C6, N6, G3, F3, J3, K3, and H2 each include 20 gadolinium rods and 244 uranium rods. The first new fuel assemblies at G14, J14, E13, L13, C11, N11, B9, P9, B7, P7, C5, N5, E3, L3, G2, and J2 each include 8 gadolinium rods and 256 uranium rods. The first new fuel assemblies at D12, M12, D4, and M4 each include 16 gadolinium rods and 248 uranium rods.

[0044] Further integration Figure 1 Among the 32 second new fuel assemblies, the second new fuel assemblies at G11, E11, J11, L11, G9, E9, J9, L9, G7, E7, J7, L7, G5, E5, J5, and L5 each include 24 gadolinium rods and 240 uranium rods; the second new fuel assemblies at F12, K12, H10, F10, D10, K10, M10, F8, K8, H6, F6, D6, K6, M6, F4, and K4 each include 20 gadolinium rods and 244 uranium rods.

[0045] In the above embodiment, when managing the core fuel, by adjusting the number of gadolinium rods in each of the first new fuel assembly and the second new fuel assembly, the fuel loading structure with a cycle length of more than 550 days can meet the preset power conditions, safety conditions, etc.

[0046] exist Figure 2In the embodiment shown, the core is 157 cores, the total number of new fuel assemblies is 64, the number N1 of the first new fuel assemblies with an enrichment of 4.95% is 32, and the number N2 of the second new fuel assemblies with an enrichment of 4.45% is 32, and the corresponding cycle length is more than 460-470 days. In addition, regarding the 93 old fuel assemblies, the number of old fuel assemblies with an enrichment of 4.45% is 60, and the number of old fuel assemblies with an enrichment of 4.95% is 33. At this time, the core composition is shown in Table 2, where N-2 represents the fuel assemblies unloaded in the first two cycles of the current cycle, and the long cycle represents the fuel assemblies unloaded in the previous cycle.

[0047]

[0048] Table 2

[0049] Combination Figure 2 and Table 2, the loading positions of the 32 first new fuel assemblies are: H14, G14, J14, E13, F13, L13, K13, D12, M12, C11, N11, C10, N10, B9, P9, B8, P8, B7, P7, C6, N6, C5, N5, D4, M4, E3, F3, L3, K3, H2, G2, J2; the loading positions of the 32 second new fuel assemblies are: G13, J13, H12, G11, E11, J11, L11, F10, K10, G9, E9, C9, J9, L9, N9, D8, M8, G7, E7, C7, J7, L7, N7, F6, K6, G5, E5, J5, L5, H4, G3, J3. Such a loading structure not only allows the cycle length to be 460-470 days, but also meets the power and safety conditions of the core design. In addition, since the new fuel assemblies are placed in the secondary outer ring and the inner part, and the old fuel assemblies are placed in the outer ring, neutron leakage can be minimized.

[0050] Further integration Figure 2 Among the 32 first new fuel assemblies, the first new fuel assemblies at H14, G14, J14, E13, L13, D12, M12, C11, N11, B9, P9, B8, P8, B7, P7, C5, N5, D4, M4, E3, L3, H2, G2, and J2 each include 8 gadolinium rods and 256 uranium rods; the first new fuel assemblies at F13, K13, C10, N10, C6, N6, F3, and K3 each include 16 gadolinium rods and 248 uranium rods.

[0051] Further integration Figure 2 The 32 second new fuel assemblies each include 16 gadolinium rods and 248 uranium rods.

[0052] In the above embodiment, when managing the core fuel, by selecting the number of gadolinium rods in each first new fuel assembly and second new fuel assembly, the fuel loading structure with a cycle length of 460-470 days can meet the preset power conditions, safety conditions, etc.

[0053] In summary, long and short alternating balancing cycles can be used to manage fuel assemblies. The long balancing cycle can be more than 550 days, with 32 groups of new fuel assemblies with an enrichment of 4.45% and 40 groups of new fuel assemblies with an enrichment of 4.95% added to the reactor; the short balancing cycle is about 460-470 days, with 32 groups of new fuel assemblies with an enrichment of 4.45% and 32 groups of new fuel assemblies with an enrichment of 4.95% added to the reactor. In addition, some new fuel assemblies use gadolinium-containing burnable poison rods as needed.

[0054] Figure 3 1 is a flow chart of a first embodiment of a fuel management method for a core balance cycle of the present invention. The fuel management method of this embodiment includes:

[0055] Step S10, determining the cycle length corresponding to each overhaul according to the overhaul plan information of the nuclear power unit;

[0056] Step S20, for each overhaul, determine the number N1 and loading positions of the first new fuel assemblies with an enrichment of 4.95%, and the number N2 and loading positions of the second new fuel assemblies with an enrichment of 4.45% according to the determined cycle length, so as to obtain the fuel loading structure of the overhaul, wherein N1 and N2 are natural numbers, and are related to the cycle length of the core balance cycle, and the cycle length includes more than 550 days and 460-470 days; in the radial direction of the core, N1 of the first new fuel assemblies and N2 of the second new fuel assemblies are arranged in the sub-outer circle and the inner part of the core, and the N1 of the first new fuel assemblies are arranged around the N2 of the second new fuel assemblies; the N1 of the first new fuel assemblies are respectively axially symmetric with respect to the two symmetry axes of the core, and are centrosymmetric with respect to the center point of the core, and the N2 of the second new fuel assemblies are respectively axially symmetric with respect to the two symmetry axes of the core, and are centrosymmetric with respect to the center point of the core;

[0057] Step S30, respectively simulate and analyze the fuel loading structure of each overhaul, and respectively determine whether the corresponding preset conditions are met, such as power conditions, safety conditions, etc. If so, execute step S40; if not, re-execute step S20 to re-acquire the fuel loading structure;

[0058] Step S40, taking the obtained fuel loading structure as the final fuel loading structure, and performing fuel replacement of the fuel assembly according to the corresponding final fuel loading structure when performing the corresponding overhaul.

[0059] Furthermore, in step S20, when acquiring the corresponding fuel loading structure, the number of gadolinium rods in each of the first new fuel assemblies and each of the second new fuel assemblies is also determined.

[0060] The technical solution of this embodiment realizes fuel management of long and short balanced cycles by adjusting the enrichment, quantity and ratio of new fuel assemblies entering the stack, and the long and short cycles reach more than 550 days and 460-470 days respectively, solving the problem of overhaul window matching, avoiding frequent and ultra-long extended operation of the unit, improving the safety level of the unit, and contributing to power grid security. After the overhaul window is optimized, the following good effects can be brought: 1. Increase the revenue of the electricity market; 2. Improve the flexibility of overhaul planning, reduce the overlap of overhauls, and reduce the cost of overhaul; 3. Optimize the equivalent load reduction days during the National Day holiday and reduce the loss of online electricity. In addition, the number of new fuel assemblies entering the stack is reduced, the resource utilization rate is improved, the spent fuel reprocessing work is reduced, and it is more environmentally friendly.

[0061] The present invention also constructs a fuel management system for a core balancing cycle, which includes a processor and a memory storing a computer program. When the processor executes the computer program, the steps of the fuel management method for the core balancing cycle described above are implemented.

[0062] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of the claims of the present application.

Claims

1. A fuel loading structure for a core balance cycle, characterized in that: The invention comprises N1 first new fuel assemblies with an enrichment of 4.95% and N2 second new fuel assemblies with an enrichment of 4.45%, wherein N1 and N2 are natural numbers and are related to the cycle length of the core balance cycle, and the cycle length includes more than 550 days and 460-470 days; In the radial direction of the core, N1 of the first new fuel assemblies and N2 of the second new fuel assemblies are arranged in the sub-outer circle and the interior of the core, and N1 of the first new fuel assemblies are arranged around the N2 of the second new fuel assemblies; the N1 of the first new fuel assemblies are axially symmetric with respect to the two symmetry axes of the core and are centrally symmetric with respect to the center point of the core, and the N2 of the second new fuel assemblies are axially symmetric with respect to the two symmetry axes of the core and are centrally symmetric with respect to the center point of the core.

2. The fuel loading structure of the core balance cycle according to claim 1, characterized in that: When the core is 157 core and the cycle length is more than 550 days, N1 is 40, N2 is 32, and in the core coordinate system with the horizontal axis being AR and the vertical axis being 1-15, The loading positions of the 40 first new fuel assemblies are: H14, G14, J14, G13, F13, E13, J13, K13, L13, D12, M12, C11, N11, C10, N10, B9, C9, P9, N9, B8, P8, B7, C7, P7, N7, C6, N6, C5, N5, D4, M4, G3, F3, E3, J3, K3, L3, H2, G2, J2; The loading positions of the 32 second new fuel assemblies are: F12, K12, G11, E11, J11, L11, H10, F10, D10, K10, M10, G9, E9, J9, L9, F8, K8, G7, E7, J7, L7, H6, F6, D6, K6, M6, G5, E5, J5, L5, F4, K4.

3. The fuel loading structure of the core balance cycle according to claim 2, characterized in that: Among the 40 first new fuel assemblies, The first new fuel assemblies at H14, G13, F13, J13, K13, C10, N10, C9, N9, B8, P8, C7, N7, C6, N6, G3, F3, J3, K3, and H2 each include 20 gadolinium rods and 244 uranium rods; The first new fuel assemblies at G14, J14, E13, L13, C11, N11, B9, P9, B7, P7, C5, N5, E3, L3, G2, and J2 each include 8 gadolinium rods and 256 uranium rods; The first new fuel assemblies at D12, M12, D4, and M4 each include 16 gadolinium rods and 248 uranium rods.

4. The fuel loading structure for core balance cycle according to claim 2, characterized in that: Of the 32 second new fuel assemblies, The second new fuel assemblies at G11, E11, J11, L11, G9, E9, J9, L9, G7, E7, J7, L7, G5, E5, J5, and L5 each include 24 gadolinium rods and 240 uranium rods; The second new fuel assemblies at F12, K12, H10, F10, D10, K10, M10, F8, K8, H6, F6, D6, K6, M6, F4, and K4 each include 20 gadolinium rods and 244 uranium rods.

5. The fuel loading structure for core balance cycle according to claim 1, characterized in that: When the core is 157 core and the cycle length is 460-470 days, N1 is 32, N2 is 32, and in the core coordinate system with AR as the abscissa and 1-15 as the ordinate, The loading positions of the 32 first new fuel assemblies are: H14, G14, J14, E13, F13, L13, K13, D12, M12, C11, N11, C10, N10, B9, P9, B8, P8, B7, P7, C6, N6, C5, N5, D4, M4, E3, F3, L3, K3, H2, G2, J2; The loading positions of the 32 second new fuel assemblies are: G13, J13, H12, G11, E11, J11, L11, F10, K10, G9, E9, C9, J9, L9, N9, D8, M8, G7, E7, C7, J7, L7, N7, F6, K6, G5, E5, J5, L5, H4, G3, J3.

6. The fuel loading structure for core balance cycle according to claim 5, characterized in that: Among the 32 first new fuel assemblies, The first new fuel assemblies at H14, G14, J14, E13, L13, D12, M12, C11, N11, B9, P9, B8, P8, B7, P7, C5, N5, D4, M4, E3, L3, H2, G2, and J2 each include 8 gadolinium rods and 256 uranium rods; The first new fuel assemblies at F13, K13, C10, N10, C6, N6, F3, and K3 each include 16 gadolinium rods and 248 uranium rods.

7. The fuel loading structure for core balance cycle according to claim 5, characterized in that: The 32 second new fuel assemblies each consist of 16 gadolinium rods and 248 uranium rods.

8. A fuel management method for a core balance cycle, characterized in that: include: Step S10, determining the cycle length corresponding to each overhaul according to the overhaul plan information of the nuclear power unit; Step S20, for each overhaul, determine the number N1 and loading positions of the first new fuel assemblies with an enrichment of 4.95%, and the number N2 and loading positions of the second new fuel assemblies with an enrichment of 4.45% according to the determined cycle length, so as to obtain the fuel loading structure of the overhaul, wherein N1 and N2 are natural numbers, and are related to the cycle length of the core balance cycle, and the cycle length includes more than 550 days and 460-470 days; in the radial direction of the core, N1 of the first new fuel assemblies and N2 of the second new fuel assemblies are arranged in the sub-outer circle and the inner part of the core, and the N1 of the first new fuel assemblies are arranged around the N2 of the second new fuel assemblies; the N1 of the first new fuel assemblies are respectively axially symmetric with respect to the two symmetry axes of the core, and are centrosymmetric with respect to the center point of the core, and the N2 of the second new fuel assemblies are respectively axially symmetric with respect to the two symmetry axes of the core, and are centrosymmetric with respect to the center point of the core; Step S30, respectively simulate and analyze the fuel loading structure of each overhaul, and respectively determine whether the corresponding preset conditions are met, and if so, execute step S40; Step S40, taking the obtained fuel loading structure as the final fuel loading structure, and performing fuel replacement of the fuel assembly according to the corresponding final fuel loading structure when performing the corresponding overhaul.

9. The fuel management method for core balancing cycle according to claim 8, characterized in that: The step S20 further includes: The number of gadolinium rods in each of the first new fuel assemblies and each of the second new fuel assemblies is determined.

10. A fuel management system for a core balance cycle, comprising a processor and a memory storing a computer program, characterized in that: When executing the computer program, the processor implements the steps of the fuel management method for the core balancing cycle according to claim 8 or 9.

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