Long-term high-fuel-consumption fuel management method based on accident-tolerant fuel

Abstract

A long-cycle, high-burnup fuel management method based on accident-tolerant fuel, belonging to the nuclear power field, is proposed. This method targets pressurized water reactors comprising 157 fuel assemblies and includes the following steps: providing a replacement group, comprising a first-class fuel assembly and a second-class fuel assembly using accident-tolerant fuel with an enrichment of not less than 5.5%, wherein the first-class fuel assembly includes IFBA combustible poison rods, and the second-class fuel assembly includes IFBA combustible poison rods and Gd-containing combustible poison rods; during refueling, one fuel assembly and 68 remaining reserve fuel assemblies with the lowest reactivity are removed from the core center, and the remaining reserve fuel assembly with the highest reactivity from the spent fuel pool is loaded into the core center and placed into the replacement group. This method enables a long-cycle refueling of 24 months, effectively flattening core power and improving the economics of nuclear power plants.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power, specifically relating to a long-cycle high burnup fuel management method based on accident-tolerant fuel. Background Technology

[0002] Extending the refueling cycle of nuclear power plants can further improve their operational economics. Currently, the main fuel management strategy adopted by passive nuclear power plants in operation in China is 18 months, with a nominal fuel enrichment of approximately 4.95%, which is close to or has reached its limits in terms of enrichment and burnup. With advancements in accident-tolerant fuels (ATF), such as chromium-coated zirconium alloy cladding and doped large-grain fuel pellets, burnup limits and enrichment can be further improved, making a 24-month refueling cycle possible under some schemes. Currently, some technical solutions use Gd as a combustible poison, employing Gd-containing combustible poison rods to achieve a 24-month long refueling cycle. However, Gd has a high neutron absorption cross-section, making it difficult to flatten the core power, increasing the difficulty of fuel management, and affecting the overhaul intervals and service life of the unit.

[0003] For example, patent CN119904008B discloses a fuel management method using a Gd-containing combustible poison, which can achieve long-cycle fuel management with a 24-month refueling cycle in small reactors. However, Gd, as a combustible poison, has a significant impact on neutron economy, which is detrimental to core power flattening and further optimization of fuel economy.

[0004] Therefore, providing a fuel management method that can better achieve power flattening is of positive significance for further optimizing the economics of nuclear power plants. Summary of the Invention

[0005] The purpose of this invention is to provide a long-cycle, high-burnup fuel management method based on accident-tolerant fuel, thereby improving the economics of nuclear power plants.

[0006] According to one aspect of the present invention, a long-cycle high burnup fuel management method based on accident-tolerant fuel is provided for a pressurized water reactor comprising 157 fuel assemblies. The method includes the following steps:

[0007] Step a): Provide a replacement group, the replacement group comprising a first type of fuel assembly and a second type of fuel assembly, wherein the fuel rods in the first type of fuel assembly and the second type of fuel assembly are accident-tolerant fuel rods, and the accident-tolerant fuel rods have an enrichment degree of not less than 5.5%; the first type of fuel assembly includes IFBA flammable poison rods, and the second type of fuel assembly includes IFBA flammable poison rods and Gd-containing flammable poison rods; the replacement group comprises 20 first type of fuel assemblies and 48 second type of fuel assemblies; wherein each first type of fuel assembly includes 156 IFBA flammable poison rods, each second type of fuel assembly includes 200 IFBA flammable poison rods; 24 second type of fuel assemblies include 8 Gd-containing flammable poison rods, and 24 second type of fuel assemblies include 16 Gd-containing flammable poison rods;

[0008] Step b): During refueling, the fuel assembly in the center of the reactor core and 68 backup fuel assemblies with the lowest reactivity are unloaded and placed into the spent fuel pool. The remaining backup fuel assembly with the highest reactivity in the spent fuel pool is placed in the center of the reactor core and loaded into the replacement assembly. The refueling interval is 24 months.

[0009] This method, by using fuel assemblies with a mixture of IFBA combustible poison rods and Gd-containing combustible poison rods for refueling, can more effectively flatten the core power and further improve the fuel burnup limit under the premise of a long refueling cycle of 24 months, thereby optimizing the economics of nuclear power plants.

[0010] Furthermore, in some embodiments, in the second type of fuel assembly, the Gd-containing combustible poison rods are arranged in a centrosymmetric and axially symmetric manner.

[0011] Furthermore, in some embodiments, the IFBA combustible poison rods and the Gd-containing combustible poison rods are loaded in a partial length arrangement along the axis.

[0012] Furthermore, in some embodiments, the fuel consumption limit of the fuel assembly is ≤75000MWD / tU.

[0013] Furthermore, in some embodiments, in the replacement group, 20 fuel assemblies undergo 3 fuel cycles in the core, and 48 fuel assemblies undergo 2 fuel cycles in the core; after refueling, except for the fuel assemblies located in the center of the reactor core, the fuel assemblies that have undergone 2 fuel cycles are located in the radial outer layer of the core, and the fuel assemblies in the radial sub-outer layer of the core are all newly loaded fuel assemblies of the replacement group.

[0014] According to another aspect of the present invention, a long-cycle high burnup fuel management method based on accident-tolerant fuel is provided for a pressurized water reactor comprising 193 fuel assemblies. The method includes the following steps:

[0015] Step a): Provide a replacement group, the replacement group comprising a first type of fuel assembly and a second type of fuel assembly, wherein the fuel rods in the first type of fuel assembly and the second type of fuel assembly are accident-tolerant fuel rods, and the enrichment of the accident-tolerant fuel rods is not less than 6.0%; the first type of fuel assembly includes IFBA flammable poison rods, and the second type of fuel assembly includes IFBA flammable poison rods and Gd-containing flammable poison rods; the replacement group comprises 4 first type of fuel assemblies and 76 second type of fuel assemblies; each first type of fuel assembly includes 128 IFBA flammable poison rods, each second type of fuel assembly includes 156 IFBA flammable poison rods; 16 second type of fuel assemblies include 8 Gd-containing flammable poison rods, and 60 second type of fuel assemblies include 16 Gd-containing flammable poison rods;

[0016] Step b): During refueling, the fuel assembly in the center of the reactor core and 80 backup fuel assemblies with the lowest reactivity are unloaded and put into the spent fuel pool. The remaining backup fuel assembly with the highest reactivity in the spent fuel pool is placed in the center of the reactor core and loaded into the replacement group.

[0017] Furthermore, in some embodiments, in the second type of fuel assembly, the Gd-containing combustible poison rods are arranged in a centrosymmetric and axially symmetric manner.

[0018] Furthermore, in some embodiments, the IFBA combustible poison rods and the Gd-containing combustible poison rods are loaded in a partial length arrangement along the axis.

[0019] Furthermore, in some embodiments, the fuel consumption limit of the fuel assembly is ≤75000MWD / tU.

[0020] Furthermore, in some embodiments, in the replacement group, 32 fuel assemblies undergo 3 fuel cycles in the core, and 48 fuel assemblies undergo 2 fuel cycles in the core; after refueling, except for the fuel assemblies located in the center of the reactor core, the fuel assemblies that have undergone 2 fuel cycles are located in the outer radial layer of the core, and the fuel assemblies in the second outer radial layer of the core are all newly loaded fuel assemblies of the replacement group. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a partial arrangement of the balanced cycle reactor core in the first embodiment;

[0022] Figure 2This is a schematic diagram of the first type of fuel assembly structure in the first embodiment;

[0023] Figure 3 This is a schematic diagram of the second type of fuel assembly structure, which includes 8 Gd-containing combustible poison rods, as shown in the first embodiment.

[0024] Figure 4 This is a schematic diagram of the second type of fuel assembly structure, which includes 16 Gd-containing combustible poison rods, as shown in the first embodiment.

[0025] Figure 5 This is a schematic diagram of a partial arrangement of the balanced cycle reactor core in the second embodiment;

[0026] Figure 6 This is a schematic diagram of the first type of fuel assembly structure in the second embodiment;

[0027] Figure 7 This is a schematic diagram of the second type of fuel assembly structure, which includes eight Gd-containing combustible poison rods, as shown in the second embodiment.

[0028] Figure 8 This is a schematic diagram of the second type of fuel assembly structure, which includes 16 Gd-containing combustible poison rods, as shown in the second embodiment.

[0029] The purpose of the above-described drawings is to provide a detailed description of the present invention so that those skilled in the art can understand the technical concept of the invention, and is not intended to limit the invention. For the sake of brevity, the above-described drawings only schematically depict the structures related to the technical features of the present invention, and do not depict the complete structure and all details strictly according to actual scale. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0031] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment herein. The phrase appearing in various places 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 will understand that the embodiments herein can be combined with other embodiments without causing structural conflicts.

[0032] In this description, terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating relative importance or limiting the number, specific order, or primary / secondary relationship of the described technical features. In this description, "multiple" means at least two.

[0033] Long-cycle, high-burnup fuel management technology is one of the important technical means to improve the economic efficiency of nuclear power plants. In the existing passive nuclear power plant 18-month cycle fuel management method, the fuel enrichment has reached about 4.95%, and the enrichment and burnup have approached or reached the limit. With the rapid development of civilian nuclear energy technology, the demand for 24-month long-cycle fuel management methods in nuclear power plants is constantly increasing.

[0034] With the development of ATF (Accident Tolerant Fuel) technology, represented by chromium-coated zirconium alloy cladding and doped large-grained fuel pellets, fuel performance supports the average fuel rod burnup exceeding the limit of 62,000 MWd / tU, further increasing fuel enrichment to over 5%, making a 24-month refueling cycle possible. This will significantly reduce overhaul costs throughout the unit's lifespan, reduce spent fuel production, and save on spent fuel disposal costs.

[0035] In order to overcome the shortcomings of existing technologies and further improve the economic efficiency of nuclear power plants, the first embodiment of the present invention provides a long-cycle high burnup fuel management method based on accident-tolerant fuel. This method is designed for passive pressurized water reactor nuclear power plants with 157 fuel assemblies and can achieve a long fuel cycle of 24 months.

[0036] During refueling in the balancing cycle, replacement sets are provided. Each replacement set contains 68 new fuel assemblies, divided into Category I and Category II fuel assemblies. Category I fuel assemblies consist of 20 units, employing IFBA combustible poison rods. There are 156 IFBA combustible poison rods in total, and their structure is as follows... Figure 2 As shown. There are 48 Category II fuel assemblies. Each Category II fuel assembly includes both IFBA combustible poison rods and Gd-containing combustible poison rods. There are 200 IFBA combustible poison rods, and 24 Category II fuel assemblies include 8 Gd-containing combustible poison rods. Their structure is as follows... Figure 3 As shown; the remaining 24 Category II fuel assemblies include 16 Gd-containing combustible poison rods, the structure of which is as follows. Figure 4 As shown, Gd-containing combustible poison rods are arranged in the fuel assemblies in an axisymmetric and centrosymmetric manner to better flatten the core power. Both IFBA and Gd combustible poison rods are loaded with partial length axial arrangement to optimize the axial power profile throughout the cycle. The fuel rod enrichment in the replacement group is divided into three categories: 5.9% enrichment in 8 fuel assemblies; 6.2% enrichment in 40 fuel assemblies; and 6.6% enrichment in 20 fuel assemblies.

[0037] During refueling, one fuel assembly from the center of the core and the remaining 68 fuel assemblies with the lowest reactivity are unloaded and placed in the spent fuel pool. The fuel assembly with the highest remaining reactivity from all fuel assemblies in the spent fuel pool is then placed in the center of the reactor core; the fuel assemblies from the replacement group are then loaded into the core. The 1 / 4 partial loading method of the core after refueling is as follows: Figure 1 As shown, H2 represents the core center, and the lines connecting H2 and X3 form the two axes of symmetry of the core. The fuel assemblies in the core employ a low-leakage loading method. All fuel assemblies that have undergone two cycles (X1, X2, and X3) are located in the outermost layer of the core. The remaining positions in the outermost layer are occupied by the fuel assemblies with the lowest remaining reactivity that have undergone one cycle. The second outermost layer of the core is entirely filled with newly added replacement fuel assemblies (Z3).

[0038] This refueling method uses a 24-month fuel cycle. In the balance cycle, 20 fuel assemblies undergo 3 fuel cycles in the core, and 48 fuel assemblies undergo 2 fuel cycles. The core has high backup reactivity and a high power peak factor at the beginning of its lifespan. The newly loaded fuel assemblies use a mixture of IFBA and Gd combustible poisons. This reduces the core boron concentration at the beginning of its lifespan, preventing excessive boron concentration from causing positive moderator temperature feedback. It also helps to flatten the core power distribution and improve fuel economy.

[0039] This embodiment targets a passive pressurized water reactor core consisting of 157 fuel assemblies. Employing accident-tolerant fuel (ATF) technology, the fuel enrichment exceeds 5%. Under operating conditions where the burnup limit does not exceed 75,000 MWD / tU, the effective fuel utilization rate approaches the theoretically calculated limit. By using a mixture of IFBA and Gd combustible poisons, minimizing the number of new fuel assemblies added during refueling cycles, and designing a long-cycle fuel management method, the reactor balance cycle life reaches 697 equivalent full-power days, achieving the 24-month long-cycle refueling design target.

[0040] Control rods are located within 43% of the fuel assemblies in the reactor core. These control rods are divided into conditioning rods and shutdown rods. There are two types of control rods: gray control rods and black control rods. The absorber material for gray control rod assemblies is tungsten, while the absorber material for black control rod assemblies is B4C and silver-indium-cadmium (Ag-In-Cd, or AIC). The upper part is B4C, and the lower part is AIC. The B4C portion is only inserted into the core during shutdown to provide sufficient shutdown margin.

[0041] This embodiment, based on accident-tolerant fuel technology, improves fuel enrichment and fuel rod burnup limits. It employs a mixture of IFBA and Gd combustible poisons, flattens the core power, achieves a 24-month long-cycle refueling target, reduces the number of new fuel assemblies added in the balance cycle, improves fuel utilization, reduces the average annual overhaul cost of the nuclear power plant, and enhances the plant's operational economy and flexibility. B4C and AIC are used as black control rod absorber materials, ensuring sufficient shutdown margin for the core, and all core safety parameters meet design limits.

[0042] The second embodiment of the present invention provides a long-cycle, high-burnup fuel management method based on accident-tolerant fuel. This method is designed for passive pressurized water reactor nuclear power plants with 193 fuel assemblies and can achieve a long fuel cycle of 24 months.

[0043] During refueling in the balancing cycle, replacement sets are provided. Each replacement set contains 80 new fuel assemblies, divided into Category I and Category II fuel assemblies. Category I fuel assemblies consist of four units, employing IFBA (Inertial Flammable Barrel) combustible poison rods. The total number of IFBA combustible poison rods is 156, and their structure is as follows... Figure 6 As shown. There are 76 Category II fuel assemblies. Each Category II fuel assembly includes both IFBA combustible poison rods and Gd-containing combustible poison rods. There are 156 IFBA combustible poison rods, and each of the 16 Category II fuel assemblies includes 8 Gd-containing combustible poison rods. Their structure is as follows... Figure 7 As shown; the remaining 60 Category II fuel assemblies include 16 Gd-containing combustible poison rods, the structure of which is as follows. Figure 8 As shown, Gd-containing combustible poison rods are arranged in the fuel assemblies in an axisymmetric and centrosymmetric manner to better flatten the core power. Both IFBA and Gd combustible poison rods are loaded with partial length axial arrangement to optimize the axial power profile throughout the cycle. The fuel rod enrichment in the replacement group is divided into two categories: 6.0% enrichment in 40 fuel assemblies and 6.65% enrichment in 40 fuel assemblies.

[0044] During refueling, one fuel assembly from the center of the core and the remaining 80 fuel assemblies with the lowest reactivity are unloaded and placed in the spent fuel pool. The fuel assembly with the highest remaining reactivity from all fuel assemblies in the spent fuel pool is then placed in the center of the reactor core; the fuel assemblies from the replacement group are then loaded into the core. The 1 / 4 partial loading method of the core after refueling is as follows: Figure 5As shown, H2 represents the core center, and the lines connecting H2-A and H2-B form the two axes of symmetry of the core. The fuel assemblies in the core employ a low-leakage loading method. All fuel assemblies that have undergone two cycles (X1 and X2) are located in the outermost layer of the core. The remaining positions in the outermost layer are occupied by the fuel assemblies with the lowest remaining reactivity that have undergone one cycle. The second outermost layer of the core is entirely filled with newly added replacement fuel assemblies (Z2).

[0045] Using this refueling method, with a fuel cycle of 24 months, 32 fuel assemblies undergo 3 fuel cycles in the core during the balance cycle, and 48 fuel assemblies undergo 2 fuel cycles in the core.

[0046] This embodiment targets a passive pressurized water reactor core consisting of 193 fuel assemblies. It employs accident-tolerant fuel (ATF) technology, with a fuel enrichment of no less than 6.0%. Under operating conditions where the burnup limit does not exceed 75,000 MWD / tU, the effective fuel utilization rate is close to the theoretically calculated limit. By using a mixture of IFBA and Gd combustible poisons, minimizing the number of new fuel assemblies added during refueling cycles, and designing a long-cycle fuel management method, the reactor balance cycle life reaches 681 equivalent full-power days, achieving the 24-month long-cycle refueling design goal.

[0047] The purpose of the above embodiments is to provide a further detailed description of the present invention 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, optimization or equivalent substitution of the technical features involved, as well as combination of implementation methods in different embodiments without causing a conflict of principles, all fall within the protection scope of the present invention.

Claims

1. A long-cycle, high-burnup fuel management method based on accident-tolerant fuel, for a pressurized water reactor comprising 157 fuel assemblies, characterized in that, Includes the following steps: Step a): Provide a replacement group, the replacement group comprising a first type of fuel assembly and a second type of fuel assembly, wherein the fuel rods in the first type of fuel assembly and the second type of fuel assembly are accident-tolerant fuel rods, and the accident-tolerant fuel rods have an enrichment degree of not less than 5.5%; the first type of fuel assembly includes IFBA flammable poison rods, and the second type of fuel assembly includes IFBA flammable poison rods and Gd-containing flammable poison rods; the replacement group comprises 20 first type of fuel assemblies and 48 second type of fuel assemblies; wherein each first type of fuel assembly includes 156 IFBA flammable poison rods, each second type of fuel assembly includes 200 IFBA flammable poison rods; 24 second type of fuel assemblies include 8 Gd-containing flammable poison rods, and 24 second type of fuel assemblies include 16 Gd-containing flammable poison rods; Step b): During refueling, the fuel assembly in the center of the reactor core and 68 backup fuel assemblies with the lowest reactivity are unloaded and put into the spent fuel pool. The remaining backup fuel assembly with the highest reactivity in the spent fuel pool is placed in the center of the reactor core and loaded into the replacement group; the refueling interval is 24 months.

2. The long-cycle high-fuel-consumption fuel management method based on accident-tolerant fuel according to claim 1, characterized in that, In the second type of fuel assembly, the Gd-containing combustible poison rods are arranged in a centrosymmetric and axially symmetric manner.

3. The long-cycle high-fuel-consumption fuel management method based on accident-tolerant fuel according to claim 1 or 2, characterized in that, The IFBA combustible poison rods and the Gd-containing combustible poison rods are loaded in a partial length arrangement along the axis.

4. The long-cycle high-fuel-consumption fuel management method based on accident-tolerant fuel according to claim 1 or 2, characterized in that, The fuel consumption limit for the fuel assembly is ≤75000MWD / tU.

5. The long-cycle high-fuel-consumption fuel management method based on accident-tolerant fuel according to claim 1 or 2, characterized in that, In the replacement group, 20 fuel assemblies undergo 3 fuel cycles in the core, and 48 fuel assemblies undergo 2 fuel cycles in the core. After refueling, except for the fuel assemblies located in the center of the reactor core, the fuel assemblies that have undergone 2 fuel cycles are located in the outer radial layer of the core, and the fuel assemblies in the second outer radial layer of the core are all newly loaded fuel assemblies from the replacement group.

6. A long-cycle, high-burnup fuel management method based on accident-tolerant fuel, for a pressurized water reactor comprising 193 fuel assemblies, characterized in that, Includes the following steps: Step a): Provide a replacement group, the replacement group comprising a first type of fuel assembly and a second type of fuel assembly, wherein the fuel rods in the first type of fuel assembly and the second type of fuel assembly are accident-tolerant fuel rods, and the enrichment of the accident-tolerant fuel rods is not less than 6.0%; the first type of fuel assembly includes IFBA flammable poison rods, and the second type of fuel assembly includes IFBA flammable poison rods and Gd-containing flammable poison rods; the replacement group comprises 4 first type of fuel assemblies and 76 second type of fuel assemblies; each first type of fuel assembly includes 128 IFBA flammable poison rods, each second type of fuel assembly includes 156 IFBA flammable poison rods; 16 second type of fuel assemblies include 8 Gd-containing flammable poison rods, and 60 second type of fuel assemblies include 16 Gd-containing flammable poison rods; Step b): During refueling, the fuel assembly in the center of the reactor core and 80 backup fuel assemblies with the lowest reactivity are unloaded and put into the spent fuel pool. The remaining backup fuel assembly with the highest reactivity in the spent fuel pool is placed in the center of the reactor core and loaded into the replacement group.

7. The long-cycle high-fuel-consumption fuel management method based on accident-tolerant fuel according to claim 6, characterized in that, In the second type of fuel assembly, the Gd-containing combustible poison rods are arranged in a centrosymmetric and axially symmetric manner.

8. The long-cycle high-fuel-consumption fuel management method based on accident-tolerant fuel according to claim 6 or 7, characterized in that, The IFBA combustible poison rods and the Gd-containing combustible poison rods are loaded in a partial length arrangement along the axis.

9. The long-cycle high-fuel-consumption fuel management method based on accident-tolerant fuel according to claim 6 or 7, characterized in that, The fuel consumption limit for the fuel assembly is ≤75000MWD / tU.

10. The long-cycle high-fuel-consumption fuel management method based on accident-tolerant fuel according to claim 6 or 7, characterized in that, In the replacement group, 32 fuel assemblies undergo 3 fuel cycles in the reactor core, and 48 fuel assemblies undergo 2 fuel cycles in the reactor core. After refueling, except for the fuel assemblies located in the center of the reactor core, the fuel assemblies that have undergone 2 fuel cycles are located in the outer radial layer of the reactor core, and the fuel assemblies in the second outer radial layer of the reactor core are all newly loaded fuel assemblies from the replacement group.

Images