Reactor core fuel management method for small pressurized water reactor

Abstract

The invention discloses a small pressurized water reactor core fuel management method and belongs to the field of nuclear power. The method is applied to a small pressurized water reactor comprising 57 fuel assemblies, and comprises the following steps: a first batch of fuel assemblies with three different enrichment degrees are loaded in a first cycle, and the first cycle lasts for 24 months; in 5 or 6 transition cycles, 17 fuel assemblies subjected to burnup are unloaded in each cycle, 17 replacement fuel assemblies are loaded in each cycle, and the duration of the transition cycles is 21-24 months; and after the transition cycle, the fuel assemblies enter balance cycles, 17 fuel assemblies subjected to burnup are unloaded in each balance cycle, 17 replacement fuel assemblies are loaded in each balance cycle, and the balance cycle duration is 24 months. According to the method, 24-month balanced circulation and 4-batch refueling can be realized, and the economical efficiency of the small pressurized water reactor is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear power, and particularly relates to a method for managing the core fuel of a small pressurized water reactor. Background Art

[0002] Compared with large commercial pressurized water reactors, the small pressurized water reactor has a simple system structure, a small volume, and a small number of fuel assemblies loaded in the core, and the burnup shadow effect is obvious. At present, the small pressurized water reactor usually adopts a fuel management scheme of no refueling and once-through, and all the fuel is loaded and unloaded during refueling. Due to the uneven burnup of the core fuel, the fuel economy performance is not good. Patent CN108364695B discloses a fuel management method, which uses gadolinium-containing burnable poison to manage the fuel of a small pressurized water reactor. However, this method only compensates for the excess reactivity by using burnable poison rods, and the adjustment ability is limited; at the same time, the cost of gadolinium-containing burnable poison rods is relatively high, and they are less used in commercial pressurized water reactors, and the versatility is insufficient. Therefore, providing a simpler method for managing the core fuel of a small pressurized water reactor has positive significance for improving the economy of a small pressurized water reactor. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for managing the core fuel of a small pressurized water reactor, which extends the equilibrium refueling cycle of the small pressurized water reactor to 24 months.

[0004] According to an embodiment of the present invention, there is provided a method for managing the core fuel of a small pressurized water reactor, which is applicable to a small pressurized water reactor whose core includes 57 groups of 17×17 type fuel assemblies. The method includes the following steps: Step a): In the first cycle of the core of the small pressurized water reactor, the first batch of fuel assemblies with three different enrichment degrees are loaded, and the length of the first cycle is 24 months; Step b): After the first cycle, 5 or 6 transition cycles are carried out; in each of the transition cycles, 17 burned fuel assemblies are unloaded, and 17 replacement fuel assemblies are loaded; the length of each transition cycle is 21-24 months; Step c): After all the transition cycles are completed, an equilibrium cycle is entered; in each of the equilibrium cycles, 17 burned fuel assemblies are unloaded, and 17 replacement fuel assemblies are loaded; the length of each equilibrium cycle is 24 months.

[0005] Using this method, on the basis of using low-enrichment fuel below 5%, the equilibrium refueling cycle of the small pressurized water reactor can be extended to 24 months, realizing a long-cycle fuel management strategy of multi-batch loading and unloading of fuel, improving the fuel utilization rate, and improving the economy of the small pressurized water reactor.

[0006] Furthermore, in some embodiments, in step b) and step c), the 17 consumed fuel assemblies discharged include the fuel assemblies at the center of the small pressurized water reactor core and the 16 fuel assemblies with the highest degree of consumption among the remaining fuel assemblies.

[0007] Furthermore, in some embodiments, in the balancing cycle, the average batch discharge fuel consumption is 35000-37000 MWd / tU, and the maximum rod fuel consumption is 42000-45000 MWd / tU.

[0008] Furthermore, in some embodiments, the fuel assemblies in the small pressurized water reactor core adopt a low leakage loading method, and in the step a), the first batch of fuel assemblies includes a first enrichment, a second enrichment and a third enrichment, wherein the first enrichment < the second enrichment < the third enrichment; the fuel assembly arranged in the center of the small pressurized water reactor core adopts the first enrichment; the fuel assemblies at the outermost edge of the small pressurized water reactor core adopt the second enrichment; the 3×3 fuel assemblies in the middle of the small pressurized water reactor core respectively adopt the first enrichment and the second enrichment and are arranged in a checkerboard pattern; the fuel assembly using the third enrichment is separated from the outer boundary of the small pressurized water reactor core by a fuel assembly using the second enrichment.

[0009] Furthermore, in some embodiments, in the step a), the number of the fuel assemblies using the first enrichment degree is 5, the number of the fuel assemblies using the second enrichment degree is 40, and the number of the fuel assemblies using the third enrichment degree is 12.

[0010] Furthermore, in some embodiments, in the step a), the first enrichment is 0.92%, the second enrichment is 1.90%, and the third enrichment is 3.00%.

[0011] Furthermore, in some embodiments, in the step b), the replacement fuel assembly includes the fuel assembly with the highest remaining reserve reactivity in the spent fuel pool and 16 new fuel assemblies with an enrichment of 3.40%-3.50%; in the step c), the replacement fuel assembly includes the fuel assembly with the highest remaining reserve reactivity in the spent fuel pool and 16 new fuel assemblies with an enrichment of 3.50%-3.60%.

[0012] Further, in some embodiments, the fuel assemblies in the small PWR core adopt a high-leakage loading pattern. In step a), the first batch of fuel assemblies includes a first enrichment, a second enrichment, and a third enrichment, where the first enrichment < the second enrichment < the third enrichment; the fuel assemblies arranged at the center of the small PWR core adopt the first enrichment; the fuel assemblies at the outermost periphery of the small PWR core adopt the third enrichment; the 3×3 fuel assemblies in the middle of the small PWR core adopt the first enrichment and the second enrichment respectively and are arranged in a checkerboard pattern.

[0013] Further, in some embodiments, in step a), the number of fuel assemblies adopting the first enrichment is 5, the number of fuel assemblies adopting the second enrichment is 32, and the number of fuel assemblies adopting the third enrichment is 20.

[0014] Further, in some embodiments, in step a), the first enrichment is 1.40%, the second enrichment is 1.90%, and the third enrichment is 2.70%.

[0015] Further, in some embodiments, in step b), the replacement fuel assemblies include new fuel assemblies with an enrichment of 2.40% - 2.60% arranged at the center of the small PWR core and 16 new fuel assemblies with an enrichment of 3.55% - 3.65%; in step c), the replacement fuel assemblies include new fuel assemblies with an enrichment of 2.40% - 2.60% arranged at the center of the small PWR core and 16 new fuel assemblies with an enrichment of 3.40 - 3.60%.

[0016] Further, in some embodiments, during refueling, the core loading maintains a 1 / 4 rotational symmetry. Description of the Drawings

[0017] Figure 1 Schematic diagram of the loading of the first batch of fuel assemblies in one embodiment; Figure 2 Schematic diagram of the loading of the equilibrium cycle fuel assemblies in one embodiment; Figure 3 Schematic diagram of the refueling strategy of the equilibrium cycle fuel assemblies in one embodiment; Figure 4 Schematic diagram of the loading of the first batch of fuel assemblies in another embodiment; Figure 5 Schematic diagram of the loading of the equilibrium cycle fuel assemblies in another embodiment; Figure 6 Schematic diagram of the refueling strategy of the equilibrium cycle fuel assemblies in another embodiment; Figure 7Schematic diagram of the rotational symmetry relationship in the fuel assembly in an embodiment.

[0018] It should be understood that in the above drawings, each square represents a fuel assembly, and the labels in the squares only indicate the ranking of the remaining excess reactivity of the fuel assembly in the entire core of the fuel assemblies in the illustrated state, where 1 is the lowest and 4 is the highest, and * is not included in the ranking; the remaining excess reactivity of the fuel assemblies with the same label in the same drawing is approximately at the same level, but not strictly equal; the remaining excess reactivity of the fuel assemblies in different drawings cannot be directly compared according to the labels.

[0019] The purpose of the above drawings is to make a detailed description of the present invention so that those skilled in the art can understand the technical concept of the present invention, rather than to limit the present invention. For the sake of brevity, the above drawings only schematically show the structures related to the technical features of the present invention, and do not strictly draw the complete structure and all details according to the actual proportion. Detailed implementation manners

[0020] The present invention will be further described in detail below through specific embodiments in conjunction with the drawings.

[0021] The mention of "embodiment" in this article means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of this article. The phrase appearing at various positions in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments in this article can be combined with other embodiments without structural conflicts.

[0022] In the description of this article, terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating relative importance or limiting the quantity, specific order or primary-secondary relationship of the described technical features. In the description of this article, the meaning of "a plurality" is at least two.

[0023] Compared with conventional large commercial pressurized water reactors, small pressurized water reactors have lower power, smaller scale, and less fuel used in the reactor, and have more flexible application scenarios. For example, they can undertake part of the peak load when the heating load is large in winter to meet the application requirements such as residential heating, industrial gas supply, and seawater desalination.

[0024] At present, the core of small PWRs usually adopts 57 groups of 17×17 fuel assemblies, and the active section height is about 190 cm. The existing mainstream fuel management scheme is no refueling and once-through, which results in uneven fuel burnup and reduced fuel economy. Patent CN108364695B discloses a fuel management method for the core of a one-million-kilowatt reactor, which can achieve a 24-month cycle refueling period. However, this method requires the use of Gd-containing burnable poison rods with multiple different concentrations, and the fuel management scheme is complex. At the same time, the equilibrium cycle of this scheme still needs to be managed by dividing odd and even cycles respectively, and in fact, the stable and balanced cycle of fuel is not fully realized. Further, there is no soluble boron in the primary loop of this method to participate in compensating the excess reactivity, and the flexibility of power regulation is insufficient.

[0025] In order to overcome the defects of the prior art, the embodiments of the present invention provide a fuel management method for the core of a small PWR, which can stably achieve a 24-month cycle refueling period for a small PWR including 57 groups of 17×17 fuel assemblies. At the same time, in this method, the fuel assemblies adopt conventional integral burnable poisons, and there is no need to re-design the burnable poisons or fuel assemblies. Specifically, this method includes a first cycle, 5 or 6 transition cycles, and subsequent equilibrium cycles. This method includes the following steps: Step a): In the first cycle, three-batch loading is adopted, and the first batch of fuel assemblies with three different enrichments are loaded into the reactor core, and the length of the first cycle is 24 months.

[0026] Step b): Starting from the second cycle, it enters the transition cycle. At the beginning of each transition cycle, 17 burned fuel assemblies are unloaded from the reactor core, and 17 transition fuel assemblies are loaded. The length of each transition cycle is 21-22 months. Among the 17 unloaded fuel assemblies, it includes the fuel assemblies arranged at the center position of the reactor core and 16 fuel assemblies with the deepest burnup (the lowest remaining excess reactivity) among the remaining fuel assemblies.

[0027] Step c): After the transition cycle ends, it enters the equilibrium cycle. At the beginning of each equilibrium cycle, 17 burned fuel assemblies are unloaded from the reactor core, and 17 equilibrium fuel assemblies are loaded. The length of each equilibrium cycle is 24 months. In the equilibrium cycle, the average batch discharge burnup is 35000-37000 MWd / tU, and the maximum rod burnup is 42000-45000 MWd / tU.

[0028] In a preferred embodiment, the rated power of the small PWR is 200 MWt, it is loaded with 57 square 17×17 fuel assemblies, each fuel assembly includes 264 fuel rods, 24 guide tubes and 1 instrument tube, and the active zone height is 190 cm.

[0029] In the core, the fuel assemblies are loaded in a low-leakage manner (fuel assemblies with lower residual excess reactivity are arranged at the periphery of the core to reduce the radioactive leakage outside the core). Among them, the enrichments of the first batch of fuel assemblies are the first enrichment of 0.92%, the second enrichment of 1.90%, and the third enrichment of 3.00%. Among them, there are 5 first-batch fuel assemblies with an enrichment of 0.92%, 40 first-batch fuel assemblies with an enrichment of 1.90%, and 12 first-batch fuel assemblies with an enrichment of 3.00%. The number of integral burnable poison rods in each first-batch fuel assembly is 0, 44, or 88.

[0030] During loading, as Figure 1 shown, the numbers in the squares represent the residual excess reactivity of the corresponding fuel assemblies. The reactor core is radially divided into three zones. Among them, the fuel assembly E5 is located at the center of the reactor core and uses a fuel assembly with the lowest residual excess reactivity (the residual excess reactivity is denoted as 1) and an enrichment of 0.92%; the fuel assemblies at the outermost periphery of the core use fuel assemblies with a medium residual excess reactivity (the residual excess reactivity is denoted as 2) and an enrichment of 1.90%. The number of burnable poison rods in these fuel assemblies is 0; within the range of 3×3 in the middle of the reactor (coordinate range F-D, 4-6), 9 groups of fuel assemblies use fuel assemblies with enrichments of 0.92% and 1.90% arranged in a checkerboard pattern; the fuel assemblies with an enrichment of 3.00% with the highest residual excess reactivity (the residual excess reactivity is denoted as 3) are arranged in the second outermost layer of the reactor core, with a fuel assembly with an enrichment of 1.90% spaced from the outer boundary of the core. The length of the first cycle is 24 months.

[0031] Starting from the second cycle, 17 burned fuel assemblies in the core are unloaded and put into the spent fuel pool, and 17 replacement fuel assemblies are loaded. Among them, the unloaded fuel assemblies include the fuel assembly E5 at the center of the reactor core and 16 fuel assemblies with the lowest residual excess reactivity among the remaining fuel assemblies. Among the replacement fuel assemblies, one fuel assembly with the highest residual excess reactivity is selected from the spent fuel pool and installed in the E5 position to effectively flatten the power distribution near the center of the core. The remaining replacement fuel assemblies use new fuel assemblies with an enrichment of 3.45%. Each new fuel assembly includes 88 burnable poison rods. The length of the second cycle is 22 months, and the length of the subsequent 5 transition cycles is 24 months.

[0032] Starting from the 7th cycle, it enters the equilibrium cycle. At the beginning of each equilibrium cycle, 17 burned fuel assemblies in the core are unloaded and put into the spent fuel pool, and 17 replacement fuel assemblies are loaded. Among them, the unloaded fuel assemblies include the fuel assembly E5 at the center of the reactor core and the remaining 16 fuel assemblies with the lowest residual excess reactivity. The layout form of the fuel assemblies in the core during the equilibrium cycle is as Figure 2As shown in the figure, in the replacement fuel assembly, one fuel assembly with the highest remaining excess reactivity is selected from the spent fuel pool (marked with *) and installed at the E5 position to effectively flatten the power distribution near the core center; the remaining 16 replacement fuel assemblies have an enrichment of 3.50% (the remaining excess reactivity of the new fuel assembly is denoted as 4); the fuel assemblies that have experienced two cycles and three cycles and contain integral burnable poison rods (the remaining excess reactivity is denoted as 2 and 3 respectively) are arranged at the core periphery to reduce core leakage; the remaining fuel assemblies are arranged in a checkerboard pattern at the middle region of the core according to their respective different remaining excess reactivity.

[0033] Specifically, the core loading maintains 1 / 4 rotational symmetry. As Figure 7 shown, there is mirror symmetry between adjacent regions and central symmetry between diagonal regions. The shuffling strategy is as Figure 3 shown. Taking the loading of a 1 / 8 core region (region VIII in Figure 7 ) as an example for illustration: The central assembly E5 is loaded with 1 old fuel assembly with the highest excess reactivity in the spent fuel pool. The old fuel assembly at the D5 position continues to use the old fuel assembly at the C7 position, the old fuel assembly at the C5 position continues to use the old fuel assembly at the D5 position, the old fuel assembly at the A5 position continues to use the old fuel assembly at the H5 position, the old fuel assembly at the D6 position continues to use the old fuel assembly at the A5 position, the old fuel assembly at the C6 position continues to use the old fuel assembly at the A6 position, the old fuel assembly at the A6 position continues to use the old fuel assembly at the H3 position, the old fuel assembly at the B7 position continues to use the old fuel assembly at the H4 position. New fuel assemblies with a fuel enrichment of 3.50% are loaded at the B5, B6, and C7 positions; the equilibrium cycle length is 24 months. The shuffling strategy is implemented for the remaining regions according to the symmetry relationship as Figure 7 shown. The batch discharge burnup is 37000 MWd / tU, and the maximum rod burnup does not exceed 42000 MWd / tU.

[0034] In another preferred embodiment, the small pressurized water reactor has a rated power of 200 MWt, loads 57 square 17×17 type fuel assemblies, each fuel assembly includes 264 fuel rods, 24 guide tubes and 1 instrumentation tube, and the active zone height is 190 cm.

[0035] The fuel assemblies in the core adopt a high leakage loading mode. Among them, the enrichments of the first batch of fuel assemblies are the first enrichment of 1.40%, the second enrichment of 1.90% and the third enrichment of 2.70%. There are 5 first batch fuel assemblies with an enrichment of 1.40%, 32 first batch fuel assemblies with an enrichment of 1.90%, and 20 first batch fuel assemblies with an enrichment of 2.70%. The number of integral burnable poison rods in each first batch fuel assembly is 0, 44 or 64.

[0036] When loading, as Figure 4As shown in the figure, the numbers in the squares represent the remaining excess reactivity of the corresponding fuel assemblies. The reactor core is radially divided into three zones. Among them, the fuel assembly E5 is located at the center of the reactor core and uses a fuel assembly with the lowest remaining excess reactivity (the remaining excess reactivity is denoted as 1) and an enrichment of 1.40%; the fuel assemblies at the outermost periphery of the core use fuel assemblies with the highest remaining excess reactivity (the remaining excess reactivity is denoted as 3) and an enrichment of 2.70%; within the 3×3 range (coordinate range F-D, 4-6) in the middle of the reactor, 9 groups of fuel assemblies use fuel assemblies with enrichments of 1.40% and 1.90% (the remaining excess reactivity is denoted as 2) and are arranged in a checkerboard pattern; the remaining positions are filled with the remaining fuel assemblies with an enrichment of 1.90%. The length of the first cycle is 24 months.

[0037] Starting from the second cycle, 17 burned fuel assemblies in the core are unloaded and put into the spent fuel pool, and 17 replacement fuel assemblies are loaded. Among them, the unloaded fuel assemblies include the fuel assembly E5 at the center of the reactor core and 16 fuel assemblies with the lowest remaining excess reactivity among the remaining fuel assemblies. Among the replacement fuel assemblies, a new fuel assembly with an enrichment of 2.50% is installed at the E5 position, and the remaining replacement fuel assemblies use new fuel assemblies with an enrichment of 3.60%. Each new fuel assembly includes 44 burnable poison rods. The length of the second cycle is 23 months, and the length of the subsequent 5 transition cycles is 24 months.

[0038] Starting from the 7th cycle, it enters the equilibrium cycle. At the beginning of each equilibrium cycle, 17 burned fuel assemblies in the core are unloaded and put into the spent fuel pool, and 17 replacement fuel assemblies are loaded. Among them, the unloaded fuel assemblies include the fuel assembly E5 at the center of the reactor core and the other 16 fuel assemblies with the lowest remaining excess reactivity. The layout form of the fuel assemblies in the core during the equilibrium cycle is as Figure 5 shown. Among the replacement fuel assemblies, a new fuel assembly with an enrichment of 2.5% (marked as *) is installed at the E5 position. The fuel assembly includes 44 integral burnable poison rods; the remaining 16 replacement fuel assemblies use an enrichment of 3.45% (the remaining excess reactivity of the new fuel assembly is denoted as 4) and are all arranged at the periphery of the core to flatten the radial power distribution of the core; the remaining fuel assemblies that have experienced one, two, and three cycles are arranged in a checkerboard pattern in the central area of the core.

[0039] Specifically, the core loading maintains 1 / 4 rotational symmetry, as Figure 7 shown. There is mirror symmetry between adjacent regions and central symmetry between diagonal regions. The refueling strategy is as Figure 6 shown. Taking a 1 / 8 core region ( Figure 7Taking the loading of Region VIII) in it as an example for illustration: The central component E5 is loaded with fuel assemblies with an enrichment of 2.50%. The old component at the G3 position is used at the D5 position, the old component at the J6 position is used at the C5 position, the old component at the G5 position is used at the B5 position, the old component at the A6 position is used at the A5 position, the old component at the G6 position is used at the D6 position, the old component at the F8 position is used at the C6 position, the old component at the B7 position is used at the B6 position. New fuel assemblies with a fuel enrichment of 3.45% are loaded at the A6 and B7 positions. Each group of new fuel assemblies contains 44 or 64 integral burnable poison rods; the remaining regions execute the shuffling strategy according to the symmetry relationship as Figure 7 shown. The equilibrium cycle length is 24 months. The batch discharge burnup is 35000 MWd / tU, and the maximum rod burnup does not exceed 44500 MWd / tU.

[0040] The small PWR core fuel management method provided by the above embodiments can effectively improve the fuel utilization efficiency and economy of small PWRs, achieve 4-batch refueling with a cycle of 24 months under equilibrium cycle, and improve the operation reliability and flexibility of small PWRs. According to different layout modes (high leakage, low leakage), different fuel management strategies are implemented, which can achieve clean heating, serve as a backup heat source for winter heating projects, undertake part of the peak load when the winter heating load is large, and meet the application requirements of multiple scenarios such as heating for residents, industrial steam supply, and seawater desalination.

[0041] The purpose of the above embodiments is to make a further detailed description of the present invention in combination with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope disclosed by the present invention, optimizing or equivalently replacing the technical solutions involved, and combining the implementation manners in different embodiments without conflict in structure and principle all fall within the protection scope of the present invention.

Claims

1. A method for managing fuel in a small pressurized water reactor core, wherein the small pressurized water reactor core comprises 57 groups of 17×17 fuel assemblies, characterized in that: The fuel assembly adopts an integral burnable poison, and the small pressurized water reactor core fuel management method comprises the following steps: Step a): In the first cycle of the small pressurized water reactor core, the first batch of fuel assemblies with three different enrichments are loaded, and the length of the first cycle is 24 months; Step b): after the first cycle, 5 or 6 transition cycles are performed; in each transition cycle, 17 fuel assemblies that have been burned up are unloaded and 17 replacement fuel assemblies are loaded; the length of each transition cycle is 21-24 months; Step c): After all the transition cycles are completed, a balancing cycle is entered; in each balancing cycle, 17 consumed fuel assemblies are unloaded and 17 replacement fuel assemblies are loaded; the length of each balancing cycle is 24 months.

2. The small pressurized water reactor core fuel management method according to claim 1, characterized in that: In the step b) and the step c), the 17 burned-up fuel assemblies discharged include the fuel assembly at the center of the small pressurized water reactor core and the 16 fuel assemblies with the highest degree of burn-up among the remaining fuel assemblies.

3. The small pressurized water reactor core fuel management method according to claim 1, characterized in that: In the balancing cycle, the average batch discharge fuel consumption is 35000-37000 MWd / tU, and the maximum rod fuel consumption is 42000-45000 MWd / tU.

4. The small pressurized water reactor core fuel management method according to claim 1, 2 or 3, characterized in that: The fuel assemblies in the small pressurized water reactor core adopt a low leakage loading method. In the step a), the first batch of fuel assemblies include a first enrichment, a second enrichment and a third enrichment, wherein the first enrichment < the second enrichment < the third enrichment; the fuel assembly arranged in the center of the small pressurized water reactor core adopts the first enrichment; the fuel assemblies at the outermost edge of the small pressurized water reactor core adopt the second enrichment; the 3×3 fuel assemblies in the middle of the small pressurized water reactor core respectively adopt the first enrichment and the second enrichment and are arranged in a checkerboard pattern; the fuel assembly using the third enrichment is separated from the outer boundary of the small pressurized water reactor core by a fuel assembly using the second enrichment.

5. The small pressurized water reactor core fuel management method according to claim 4, characterized in that: In the step a), the number of the fuel assemblies using the first enrichment degree is 5, the number of the fuel assemblies using the second enrichment degree is 40, and the number of the fuel assemblies using the third enrichment degree is 12.

6. The small pressurized water reactor core fuel management method according to claim 5, characterized in that: In the step a), the first enrichment is 0.92%, the second enrichment is 1.90%, and the third enrichment is 3.00%.

7. The small pressurized water reactor core fuel management method according to claim 6, characterized in that: In the step b), the replacement fuel assembly includes the fuel assembly with the highest remaining reserve reactivity in the spent fuel pool and 16 new fuel assemblies with an enrichment of 3.40%-3.50%; in the step c), the replacement fuel assembly includes the fuel assembly with the highest remaining reserve reactivity in the spent fuel pool and 16 new fuel assemblies with an enrichment of 3.50%-3.60%.

8. The small pressurized water reactor core fuel management method according to claim 1, 2 or 3, characterized in that: The fuel assemblies in the small pressurized water reactor core adopt a high leakage loading method. In the step a), the first batch of fuel assemblies include a first enrichment, a second enrichment and a third enrichment, wherein the first enrichment < the second enrichment < the third enrichment; the fuel assembly arranged in the center of the small pressurized water reactor core adopts the first enrichment; the fuel assemblies at the outermost periphery of the small pressurized water reactor core adopt the third enrichment; the 3×3 fuel assemblies in the middle of the small pressurized water reactor core respectively adopt the first enrichment and the second enrichment and are arranged in a checkerboard manner.

9. The small pressurized water reactor core fuel management method according to claim 8, characterized in that: In the step a), the number of the fuel assemblies using the first enrichment degree is 5, the number of the fuel assemblies using the second enrichment degree is 32, and the number of the fuel assemblies using the third enrichment degree is 20.

10. The small pressurized water reactor core fuel management method according to claim 9, characterized in that: In the step a), the first enrichment is 1.40%, the second enrichment is 1.90%, and the third enrichment is 2.70%.

11. The small pressurized water reactor core fuel management method according to claim 10, characterized in that: In the step b), the replacement fuel assembly includes a new fuel assembly with an enrichment of 2.40%-2.60% and 16 new fuel assemblies with an enrichment of 3.55%-3.65% arranged at the center of the small pressurized water reactor core; in the step c), the replacement fuel assembly includes a new fuel assembly with an enrichment of 2.40%-2.60% and 16 new fuel assemblies with an enrichment of 3.40-3.60% arranged at the center of the small pressurized water reactor core.

12. The small pressurized water reactor core fuel management method according to claim 1, 2 or 3, characterized in that: During refueling, the core loading maintains 1 / 4 rotational symmetry.

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