Combustible poison loading method for reducing tritium emission of nuclear power plant

Abstract

The invention discloses a burnable poison loading method for reducing tritium emission of a nuclear power plant and belongs to the field of nuclear power. The method comprises the following steps: providing a first type fuel assembly adopted by a reactor, providing a tritium-reduced burnable poison rod, and loading discrete water-through annular burnable poison or Gd-containing burnable poison in the tritium-reduced burnable poison rod; at least part of the integral burnable poison fuel rods in the first type of fuel assemblies are replaced with tritium-reduced burnable poison rods to obtain second type of fuel assemblies, iterative calculation is carried out to obtain second type of fuel assembly structures meeting safety design requirements, and the second type of fuel assemblies are used for fuel replacement. According to the method, the tritium-reducing burnable poison rod with longer burnup time is utilized, so that the requirement for soluble boron in a primary loop is reduced, and the effect of reducing tritium emission is achieved.

Description

Technical Field

[0001] The invention belongs to the field of nuclear power, and in particular relates to a method for loading combustible poisons for reducing tritium emissions from nuclear power plants. Background Art

[0002] As the safety performance and environmental protection requirements of nuclear power plants are increasingly improved, the emission of radioactive substances during the operation of nuclear power plants has also received more and more attention. Before the discharge of nuclear power plant wastewater, it will be treated to remove most of the radioactive nuclides, but the radioactive isotope of hydrogen, tritium, is difficult to be completely separated due to its physical and chemical properties. At present, tritium has become the main source of radioactivity in the wastewater of pressurized water reactor nuclear power plants of all types in the world. Under normal conditions, the tritium emissions of modern commercial pressurized water reactor nuclear power plants meet the tritium emission standards of the International Atomic Energy Agency, but further reducing tritium emissions will still help improve the environmental friendliness of nuclear power plants. The main source of tritium is the primary circuit of nuclear power plants, in which the soluble boron in the primary circuit coolant reacts to produce tritium, which is an important source of tritium in the primary circuit. The main function of soluble boron is to compensate for the backup reactivity of fuel assemblies during the operation of nuclear power plants. Therefore, providing a technical solution to optimize the backup reactivity of fuel assemblies and reduce the concentration of soluble boron in the primary circuit by loading burnable poisons is of positive significance for reducing tritium emissions from nuclear power plants. Summary of the invention

[0003] The object of the present invention is to provide a burnable poison loading method for reducing tritium emissions in nuclear power plants, and to reduce the soluble boron concentration in a primary loop by optimizing the burnable poison design.

[0004] According to an embodiment of the present invention, a burnable poison loading method for reducing tritium emission in a nuclear power plant is provided, wherein the reactor core of the nuclear power plant adopts a first type of fuel assembly, wherein the first type of fuel assembly comprises a common fuel rod and an integral burnable poison rod, and the method comprises the following steps: Step a): providing a reactor core model and providing the first type of fuel assembly model based on the first type of fuel assembly; Step b): Establishing a second type of fuel assembly model, wherein the second type of fuel assembly model is obtained by: Part of the integral burnable poison fuel rods in the first type fuel assembly model are replaced with ordinary fuel rods, and Replacing at least part of the remaining integral burnable poison fuel rods with detritium-reduced burnable poison rods, or adding detritium-reduced burnable poison rods in the guide tubes of the fuel assembly; wherein the detritium-reduced burnable poison rods are loaded with discrete water-permeable annular burnable poison or Gd-containing burnable poison; Based on the reactor core model, simulate and calculate whether the reactor core after the first type of fuel assembly that has been consumed in the reactor core is replaced by the second type of fuel assembly during refueling meets the safety design requirements of the reactor; step c): when the calculation result of the step b) does not meet the safety design requirements, adjust the number of tritium-reducing burnable poison rods in the second type of fuel assembly model and the arrangement position of the fuel assembly in the reactor core model, and repeat the calculation process in the step b) until the calculation result meets the safety design requirements; Step d): According to the second type fuel assembly model obtained in step c), provide a corresponding second type fuel assembly and use the second type fuel assembly to perform fuel replacement.

[0005] The method utilizes the neutron absorption performance of discrete water-circulating ring-shaped burnable poisons or Gd-containing burnable poisons in tritium-reducing burnable poison rods, so that the tritium-reducing poison rods can compensate for the core backup reactivity for a longer period of time during reactor operation, thereby reducing the demand for soluble boron in the primary coolant, achieving the effect of reducing the soluble boron concentration and thereby reducing tritium emissions generated by the primary soluble boron.

[0006] Furthermore, in some embodiments, in the step a), the tritium-reducing burnable poison rod using the discrete water-permeable annular burnable poison adopts a non-full-length structure in the axial direction of the second type of fuel assembly, and is arranged in an asymmetric manner relative to the axial midpoint of the second type of fuel assembly.

[0007] Further, in some embodiments, in the step a), the tritium-reducing burnable poison rod loaded with the discrete water-flowing annular burnable poison comprises an outer cladding tube and an inner cladding tube, and the water-flowing annular burnable poison is arranged between the outer cladding tube and the inner cladding tube.

[0008] Furthermore, in some embodiments, the reactor core includes 157 groups of fuel assemblies, and during each fuel replacement, 64 groups of the second type of fuel assemblies are used to replace the consumed fuel assemblies in the reactor core.

[0009] Furthermore, in some embodiments, in the step a), 64 groups of the first type of fuel assemblies are provided, and a total of at least 2000 integral burnable poison fuel rods therein are replaced with the ordinary fuel rods.

[0010] Furthermore, in some embodiments, in the step c), the 64 groups of the second type of fuel assemblies used for fuel replacement include a total of at least 600 tritium-reducing burnable poison rods using the discrete water-permeable annular burnable poison.

[0011] Furthermore, in some embodiments, in the step c), the 64 groups of the second type fuel assemblies used for fuel replacement include no more than 6,000 integral burnable poison fuel rods in total.

[0012] Furthermore, in some embodiments, in the step c), in the 64 groups of the second type fuel assemblies used for fuel replacement, the tritium-reducing burnable poison rods use discrete water-permeable annular burnable poisons; among them, 8 groups of the second type fuel assemblies are provided with 4 tritium-reducing burnable poison rods, 8 groups of the second type fuel assemblies are provided with 12 tritium-reducing burnable poison rods, and 36 groups of the second type fuel assemblies are provided with 16 tritium-reducing burnable poison rods.

[0013] Furthermore, in some embodiments, after the fuel is replaced by the second type of fuel assembly in the step c), the average soluble boron concentration of the first-loop coolant is reduced by at least 10% compared with the use of the first type of fuel assembly, and the average life of the second type of fuel assembly is not shorter than 95% of the average life of the first type of fuel assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a critical soluble boron concentration curve of a circuit in a comparative example; Figure 2 A schematic diagram of the arrangement of the first type of fuel assembly in one embodiment; Figure 3 A schematic diagram of the arrangement of the second type of fuel assembly in one embodiment; Figure 4 A comparison curve of critical soluble boron concentration in a circuit of an embodiment and a comparative example; Figure 5 A comparison curve of heat pipe factor of nuclear heat flux density of an embodiment and a comparative example; Figure 6 A comparison curve of the heat pipe factor of nuclear enthalpy rise of an embodiment and a comparative example; Figure 7 A schematic diagram of the arrangement of the second type of fuel assembly in another embodiment; Figure 8 A comparison curve of critical soluble boron concentration in one circuit between another embodiment and a comparative example; Fig. 9 A comparison curve of heat pipe factor of nuclear heat flux density of another embodiment and a comparative example; Fig.10 is a comparison curve of heat pipe factor of nuclear enthalpy rise of another embodiment and a comparative example; Fig.11 Schematic diagram of the cross-sectional structure of a tritium-reducing burnable poison rod using a discrete water-passing annular burnable poison in one embodiment.

[0015] The meaning of the reference numerals: 1 - guide tube; 2 - outer shell tube; 3 - water-permeable annular combustible poison; 4 - inner shell tube.

[0016] The purpose of the above drawings is to explain the present invention in detail so that those skilled in the art can understand the technical concept of the present invention, but not to limit the present invention. For the sake of simplicity, the above drawings only schematically illustrate the structures related to the technical features of the present invention, and do not strictly follow the actual proportions to draw the complete structure and all details. DETAILED DESCRIPTION

[0017] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0018] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The phrase appearing in various locations 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 herein may be combined with other embodiments without causing structural conflicts.

[0019] In the description of this article, the terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating relative importance or limiting the quantity, specific order or primary and secondary relationship of the described technical features. In the description of this article, the meaning of "plurality" is at least two.

[0020] Currently, tritium is an important source of radioactivity in wastewater discharged from pressurized water reactor nuclear power plants. The main sources of tritium include: Ternary fission in the fuel produces tritium, which penetrates through the fuel cladding and enters the primary coolant; B10 in the core burnable poison reacts with neutrons 10 B(n,2α)T reaction and 10 B(n,α) 7 The Li(n,nα)T reaction produces tritium, which penetrates into the primary coolant through the shell containing the burnable poison; The secondary neutron source rod 9 B(n,α) 6 He(β - )Li(n,α)T reaction produces tritium, which penetrates into the primary coolant through the secondary neutron source rod; and the occurrence of soluble boron in the primary coolant 10 B(n,2α)T reaction and 6 Li(n,α)T and other reactions produce tritium.

[0021] However, the current technical solutions for reducing tritium emissions are mainly aimed at tritium emissions generated by secondary neutron source rods. For example, patents CN209374067U and CN114220562A respectively proposed optimized secondary neutron source rod structures to reduce the generation of tritium during the service of secondary neutron source rods; the document "Benefit Analysis of Canceling Secondary Neutron Source Technology" (Today's Automation, 2020.06) proposed a solution to cancel the secondary neutron source rod.

[0022] However, among the above tritium sources, the contribution of the secondary neutron source rod to tritium emission is only about 12%; the contribution of soluble boron in the primary coolant is 10 The B(n,2α)T reaction is the main pathway for producing tritium, usually accounting for more than 60% of the total tritium emissions. Therefore, reducing the boron concentration in the primary coolant during the fuel cycle can effectively reduce the production of tritium.

[0023] In a pressurized water reactor, the soluble boron in the primary loop is mainly used to compensate for the core reserve reactivity. At the beginning of the fuel cycle, due to the low fuel burnup, the core reserve reactivity needs to be controlled to prevent the core power from being too high. The compensation of the reserve reactivity depends on the soluble boron in the primary loop on the one hand, and on the control rods and burnable poisons on the other hand. The use of burnable poisons is mainly used to control the excess reactivity of the core part, reduce the initial soluble boron concentration, so that the moderator temperature coefficient is not positive, and is used to flatten the radial power distribution of the core. During the core burnup process, the neutron absorbers in the burnable poison react with neutrons and are consumed, gradually releasing the core reserve reactivity. At present, some pressurized water reactor nuclear power plants use integral burnable poison fuel rods (IFBA). The loading amount of burnable poison is determined during the core design, and its loading amount is usually determined according to the restriction condition that the moderator temperature coefficient is not positive. At present, some technical solutions disclose discrete water annular burnable poison (WABA) or burnable poison containing Gd, but for commercial nuclear power plants using integral burnable poison fuel rods (IFBA), there is no technical solution to reduce tritium emissions by adjusting the burnable poison. Figure 1 As shown, in the initial stage of the fuel cycle, the critical soluble boron concentration decreases rapidly due to the establishment of the equilibrium tritium poisoning level; then, as the consumption rate of burnable poison in IFBA is greater than the fuel burnup, the critical soluble boron concentration rises again, and after the burnable poison is exhausted, it decreases monotonically with the increase of the fuel burnup depth. Patent CN118299081A discloses a technical solution, which partially replaces the compensation effect of soluble boron in the primary coolant on the backup reactivity by maintaining the insertion state of some low-value control rods in the core, thereby achieving the effect of reducing the soluble boron concentration. However, this technical solution will cause the reactor to lose the ability to track the load without adjusting the boron, and the engineering application value is relatively limited.

[0024] In order to solve the above problems, an embodiment of the present invention provides a burnable poison loading method for reducing tritium emissions in a nuclear power plant. The method is applied to a nuclear power plant using a first type of fuel assembly, i.e., a fuel assembly including ordinary fuel rods and integral burnable poison rods, in a reactor core, and includes the following steps: Step a): First, a reactor core model is provided, and a first-class fuel assembly model is provided based on the fuel assembly being used in the reactor core (i.e., the first-class fuel assembly). The first-class fuel assembly model is established based on the first-class fuel assembly. The first-class fuel assembly includes ordinary fuel rods and IFBA rods. Usually, the combustible poison in the IFBA rod adopts a ZrB2 coating coated on the surface of the fuel core block; the first-class fuel assembly model reflects the relative position relationship and reaction performance of the ordinary fuel rods and IFBA rods in the first-class fuel assembly.

[0025] Step b): Establish a second type fuel assembly model, the second type fuel assembly model includes a tritium-reduced burnable poison rod, and the tritium-reduced burnable poison rod is loaded with a discrete water-permeable annular burnable poison or a Gd-containing burnable poison.

[0026] Specifically, when a Gd-containing burnable poison is used, the cladding structure of the detritus-reduced burnable poison rod is the same as that of the IFBA rod, and the burnable poison is arranged in a dispersed form within the fuel pellet.

[0027] In a preferred embodiment, when a discrete water-through annular combustible poison is used, Fig.11 As shown, the tritium-reducing burnable poison rod can be inserted into the guide tube 1 of the fuel assembly. The tritium-reducing burnable poison rod includes an outer cladding tube 2 and an inner cladding tube 4. The water-permeable annular burnable poison 3 is arranged in the gap formed between the outer cladding tube 2 and the inner cladding tube 4. The water-permeable annular burnable poison 3 can be made of Al2O3-B4C material. Specifically, the tritium-reducing burnable poison rod using the water-permeable annular burnable poison 3 adopts a non-full-length structure in the axial direction of the second type of fuel assembly, that is, the length of the tritium-reducing burnable poison rod is less than the length of the ordinary fuel rod and the guide tube; at the same time, the tritium-reducing burnable poison rod is arranged in an asymmetric manner relative to the axial midpoint of the second type of fuel assembly, that is, the tritium-reducing burnable poison rods on both sides of the midpoint are not of equal length. The asymmetric arrangement can optimize the axial power distribution shape in the fuel cycle.

[0028] The specific structure of the second type fuel assembly model can be obtained by two schemes: in the first type of embodiment, part of the IFBA rods in the first type fuel assembly model are replaced with ordinary fuel rods, and tritium-reducing burnable poison rods using discrete water-passing annular burnable poisons are set in the guide tube of the fuel assembly; in the second type of embodiment, part of the IFBA rods in the first type fuel assembly model are replaced with ordinary fuel rods, and at least part of the remaining IFBA rods are replaced with tritium-reducing burnable poison rods containing Gd burnable poisons. The reactor core model is used to carry out calculations for the refueling scenario to determine whether the reactor core meets the power limit, power expansion and other safety design requirements of the reactor after the second type fuel assembly replaces part of the first type fuel assembly that has been burned in the reactor core for refueling. Regardless of whether the tritium-reducing fuel rod uses Gd-containing burnable poison or discrete water-passing annular burnable poison, the burnup rate of the burnable poison is slower than that of the IFBA rod. Depending on the operating state of the reactor, there are differences in the number of fuel assemblies replaced during the refueling process.

[0029] Step c): When the calculation result of step b) does not meet the safety design requirements, the number of tritium-reduced burnable poison rods in the second type of fuel rods and the arrangement of the fuel assemblies in the core are adjusted, and step b) is repeated until the calculation result of step b) meets the safety design requirements.

[0030] Step d): According to the structure of the second type fuel assembly model obtained in step c), a corresponding second type fuel assembly with a corresponding structure is provided, and these second type fuel assemblies are used for fuel replacement.

[0031] In a preferred embodiment, 157 fuel assemblies are arranged in the reactor core of a nuclear power plant, and the soluble boron concentration in the primary coolant during the fuel cycle is reduced by optimizing the burnable poison loading when performing refueling.

[0032] If the original fuel assembly is used, 64 new fuel assemblies are loaded into each refueling cycle, which contains a total of 7616 IFBA rods. Figure 2 , the newly loaded fuel assembly is marked as FEED. Figure 2 The area of ​​1 / 4 core is shown, B1 is the center of the core, and the lines connecting B1-X2 are two axes of symmetry. Figure 2 The states shown are all Class I fuel assemblies. Depending on the position of the fuel assembly in the core, the number of IFBA rods used in the newly loaded Class I fuel assembly during refueling varies. The specific number is determined according to the reactor safety design requirements. Fuel assemblies that have undergone at least one fuel cycle in the core are considered to have exhausted their combustible poisons.

[0033] The specific steps of the combustible poison loading method for reducing tritium emission in the reactor are as follows: Step a): Provide a first type of fuel assembly, these first type of fuel assemblies have the following characteristics: Figure 2 The structure is the same as the FEED marked fuel assembly shown in FIG. Tritium reduction burnable poison rods are provided, and these tritium reduction burnable poison rods use discrete water annular burnable poison (WABA) with a slower consumption rate. The discrete water annular burnable poison is contained in the guide tube of the tritium reduction burnable poison rod, and uses a partial length in the axial direction of the guide tube (that is, the total length is less than the length of the guide tube) and is arranged asymmetrically relative to the axial midpoint of the fuel assembly.

[0034] Step b): Based on the first type of fuel assembly in step a), some IFBA rods are replaced with ordinary fuel rods, and the remaining IFBA rods are at least partially replaced with tritium-reduced burnable poison rods to obtain a second type of fuel assembly. Figure 2 When the fuel assemblies marked with FEED are replaced with second-category fuel assemblies, can the safety design requirements such as core design limits and power expansion be met?

[0035] Step c): When the calculation result of step b) does not meet the safety design requirements, adjust the number of tritium-reduced burnable poison rods in the second type fuel assembly and the arrangement position of the fuel assembly in the core, and repeat the calculation in step b); repeat the above process until the calculation result meets the safety design requirements, and obtain the following Figure 3 The schematic diagram of the arrangement of the second type of fuel assembly is shown, in which the second type of fuel assembly for refueling is marked as FEED. There are 64 groups of new fuel assemblies for refueling cycle. In order to ensure that the moderator temperature coefficient is not positive and flatten the radial power distribution, a total of 5216 integral burnable poison fuel rods are added to the new fuel assemblies, reducing 2400 integral burnable poison fuel rods. A total of 704 discrete water-permeable annular burnable poison rods are added to the new fuel assemblies.

[0036] Specifically, among the newly loaded second-type fuel assemblies, 24 groups are equipped with 64 IFBA rods, 36 groups are equipped with 88 IFBA rods, 4 groups are equipped with 128 IFBA rods, 8 groups are equipped with 4 WABA tritium-reduced burnable poison rods, 8 groups are equipped with 12 WABA tritium-reduced burnable poison rods, and 36 groups are equipped with 16 WABA tritium-reduced burnable poison rods. Specifically, the number of IFBA rods and WABA tritium-reduced burnable poison rods contained in each group of fuel assemblies and their corresponding installation positions in the fuel assemblies are as follows: Figure 3 shown.

[0037] according to Figure 3 Based on the results shown, a second type of fuel assembly satisfying the corresponding conditions is provided and used for fuel replacement.

[0038] The method of loading combustible poison is similar to Figure 2As shown, compared with the comparative example using the first type of fuel assembly, the critical soluble boron concentration of the primary coolant in the embodiment is significantly reduced, and the average soluble boron concentration of the circulating coolant is reduced by 13%. Figure 4 As shown, tritium emission is effectively reduced; at the same time, the curves of the heat pipe factor of the nuclear heat flux density during the operation of the core of the embodiment and the comparative example with the core burnup are as follows Figure 5 As shown in the figure, the curve of nuclear enthalpy rise heat pipe factor changing with core burnup is as follows Figure 6 As shown, in the embodiment, the core power peak factor is slightly reduced, and the average life span of the fuel assembly changes by less than 2%, thereby maintaining the economy of the nuclear power plant operation.

[0039] In another embodiment, 157 fuel assemblies are disposed in a reactor core, and the soluble boron concentration in the primary coolant during the fuel cycle is reduced by optimizing the burnable poison loading.

[0040] In the comparative example in which only IFBA rods are used in the core, the arrangement of the first type of fuel assembly is as follows: Figure 2 The difference between this embodiment and the previous embodiment is that the tritium-reducing burnable poison rod uses a Gd-containing burnable poison in which Gd oxide is doped in uranium dioxide. The calculated fuel assembly arrangement that meets the safety design requirements is shown in Figure 7 As shown, in order to ensure that the moderator temperature coefficient is not positive and to flatten the radial power distribution, the second type of fuel assembly contains a total of 1184 Gd burnable poison fuel rods, and integral burnable poison is not used.

[0041] Specifically, among the 64 newly loaded Type II fuel assemblies, 8 Type II fuel assemblies were provided with 4 tritium-reduced burnable poison rods, 8 Type II fuel assemblies were provided with 8 tritium-reduced burnable poison rods, 20 Type II fuel assemblies were provided with 12 tritium-reduced burnable poison rods, and 28 Type II fuel assemblies were provided with 16 tritium-reduced burnable poison rods.

[0042] The method of loading combustible poison is similar to Figure 8 As shown, compared with the comparative example using the first type of fuel assembly, the critical soluble boron concentration of the primary coolant in the embodiment is significantly reduced, and the average soluble boron concentration of the circulating coolant is reduced by 19%, which effectively reduces tritium emissions; at the same time, the curves of the heat pipe factor of the nuclear heat flux density during the operation of the core of the embodiment and the comparative example with the core burnup are as shown in Fig. 9 As shown in the figure, the curve of nuclear enthalpy rise heat pipe factor changing with core burnup is as follows Fig.10 As shown, in the embodiment, the core power peak factor increases slightly at the beginning of the refueling but still meets the design limit requirements and maintains a large safety margin. The average life span change of the fuel assembly is less than 5%, maintaining the economy of the nuclear power plant operation.

[0043] The purpose of the above embodiments is to explain the present invention in detail in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, the optimization or equivalent replacement of the method steps involved, and the combination of the implementation methods in different embodiments without conflict of structure and principle, all fall within the protection scope of the present invention.

Claims

1. A burnable poison loading method for reducing tritium emission in a nuclear power plant, wherein the reactor core of the nuclear power plant adopts a first type of fuel assembly, wherein the first type of fuel assembly includes ordinary fuel rods and integral burnable poison rods, characterized in that: The following steps are involved: Step a): providing a reactor core model and providing the first type of fuel assembly model based on the first type of fuel assembly; Step b): Establish a second type of fuel assembly model, wherein the second type of fuel assembly model is obtained by: Part of the integral burnable poison fuel rods in the first type fuel assembly model are replaced with the ordinary fuel rods, and Replacing at least part of the remaining integral burnable poison fuel rods with detritium-reduced burnable poison rods, or adding detritium-reduced burnable poison rods in the guide tubes of the fuel assembly; wherein the detritium-reduced burnable poison rods are loaded with discrete water-permeable annular burnable poison or Gd-containing burnable poison; Based on the reactor core model, simulate and calculate whether the reactor core after the first type of fuel assembly that has been consumed in the reactor core is replaced by the second type of fuel assembly during refueling meets the safety design requirements of the reactor; step c): when the calculation result of the step b) does not meet the safety design requirements, adjust the number of tritium-reducing burnable poison rods in the second type of fuel assembly model and the arrangement position of the fuel assembly in the reactor core model, and repeat the calculation process in the step b) until the calculation result meets the safety design requirements; Step d): According to the second type fuel assembly model obtained in step c), provide a corresponding second type fuel assembly and use the second type fuel assembly to perform fuel replacement.

2. The method for loading combustible poisons to reduce tritium emissions from nuclear power plants according to claim 1, characterized in that: In the step a), the tritium-reducing burnable poison rod using the discrete water-permeable annular burnable poison adopts a non-full-length structure in the axial direction of the second type fuel assembly and is arranged in an asymmetric manner relative to the axial midpoint of the second type fuel assembly.

3. The method for loading combustible poisons to reduce tritium emissions from nuclear power plants according to claim 2, characterized in that: In the step a), the tritium-reducing burnable poison rod loaded with the discrete water-permeable annular burnable poison comprises an outer cladding tube and an inner cladding tube, and the water-permeable annular burnable poison is arranged between the outer cladding tube and the inner cladding tube.

4. The method for loading combustible poisons to reduce tritium emissions from nuclear power plants according to any one of claims 1 to 3, characterized in that: The reactor core includes 157 groups of fuel assemblies. During each fuel replacement, 64 groups of the second type of fuel assemblies are used to replace the consumed fuel assemblies in the reactor core.

5. The method for loading combustible poisons to reduce tritium emissions from nuclear power plants according to claim 4, characterized in that: In the step a), 64 groups of the first type of fuel assemblies are provided, and a total of at least 2000 integral burnable poison fuel rods therein are replaced with the ordinary fuel rods.

6. The method for loading combustible poisons to reduce tritium emissions from nuclear power plants according to claim 5, characterized in that: In the step c), the 64 groups of the second type of fuel assemblies used for fuel replacement include a total of at least 600 tritium-reducing burnable poison rods using the discrete water-permeable annular burnable poison.

7. The method for loading combustible poisons to reduce tritium emissions from nuclear power plants according to claim 6, characterized in that: In the step c), the 64 groups of the second type fuel assemblies used for fuel replacement include no more than 6,000 integral burnable poison fuel rods in total.

8. The method for loading combustible poisons to reduce tritium emissions from nuclear power plants according to claim 7, characterized in that: In the step c), in the 64 groups of the second type fuel assemblies used for fuel replacement, the tritium-reducing burnable poison rods use discrete water-permeable annular burnable poisons; among them, 8 groups of the second type fuel assemblies are provided with 4 tritium-reducing burnable poison rods, 8 groups of the second type fuel assemblies are provided with 12 tritium-reducing burnable poison rods, and 36 groups of the second type fuel assemblies are provided with 16 tritium-reducing burnable poison rods.

9. The method for loading combustible poisons to reduce tritium emissions from nuclear power plants according to claim 5, characterized in that: In the step c), the burnable poisons in the second type of fuel assembly used for fuel replacement are all configured in the form of the detritus burnable poison rods containing Gd burnable poison.

10. The burnable poison loading method for reducing tritium emission in a nuclear power plant according to any one of claims 1 to 3, characterized in that: After the fuel is replaced by the second type of fuel assembly in step c), the average soluble boron concentration of the primary coolant is reduced by at least 10% compared with the use of the first type of fuel assembly, and the average life of the second type of fuel assembly is not shorter than 95% of the average life of the first type of fuel assembly.

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