Long-period fuel management method based on accident fault-tolerant fuel

Abstract

A long-period fuel management method based on accident fault-tolerant fuel comprises the following steps that a replacement fuel assembly with a first enrichment degree, a second enrichment degree and a third enrichment degree is provided, and 5% lt is provided; a first enrichment degree lt; a second enrichment degree lt; according to the third enrichment degree, accident fault-tolerant fuel is adopted for the fuel replacement assembly; taking out n groups of fuel assemblies in the reactor, putting the n groups of fuel assemblies into a spent fuel pool, selecting a group of fuel assemblies with the highest backup reactivity from the spent fuel pool, arranging the selected group of fuel assemblies in the center of the reactor, and taking (n-1) groups of replacement fuel assemblies and the remaining fuel assemblies of the reactor as reloading groups; calculating an installation sequence of the refueling group according to a reactor design limit value and a safety certification condition, and carrying out installation; and the materials are repeatedly changed every 24 months. According to the method, the fuel circulation period can be prolonged to 24 months, the fuel utilization rate is effectively increased, and the economical efficiency of the nuclear power plant is improved.

Description

Technical Field

[0001] The invention belongs to the field of nuclear power, and in particular relates to a long-cycle fuel management method based on accident-tolerant fuel. Background Art

[0002] Long-cycle, high-burnup fuel management technology can significantly improve the economic efficiency of nuclear power plants. The traditional 18-month fixed refueling cycle model has become increasingly difficult to meet the needs of economic production of nuclear power plants. The 24-month refueling cycle fuel management strategy with better economy is gaining more and more attention. However, in order to achieve a 24-month fuel cycle, a large number of new fuel assemblies must be loaded each time the balance cycle is refueled. Some units need to replace more than half of the fuel assemblies at a time, which results in some fuel assemblies being unloaded after only one fuel cycle, resulting in poor fuel utilization and affecting further optimization of economy. Therefore, providing a long-cycle fuel management method with improved economy is of positive significance to improving fuel utilization and improving the economy of nuclear power plants. Summary of the invention

[0003] The purpose of the present invention is to provide a long-cycle fuel management method based on accident-tolerant fuel to improve the economic efficiency of nuclear power plant operation.

[0004] According to an embodiment of the present invention, a long-cycle fuel management method based on accident-tolerant fuel is provided, the method comprising the following steps: Step a): providing a replacement fuel assembly, wherein the replacement fuel assembly uses an accident-tolerant fuel, and the accident-tolerant fuel in the replacement fuel assembly has a first enrichment, a second enrichment, and a third enrichment, respectively, wherein 5%<first enrichment<second enrichment<third enrichment; Step b): Take out n groups of fuel assemblies in the reactor and put them into a spent fuel pool, wherein the fuel assemblies put into the spent fuel pool have undergone at least two fuel cycles, and n is not less than 1 / 3 and not more than 1 / 2 of the total number of fuel assemblies in the reactor; mix the replacement fuel assemblies of group a with a first enrichment, group b with a second enrichment, and group c with a third enrichment with the remaining fuel assemblies in the reactor to obtain a replacement group, wherein a+b+c=n-1; take out a group of fuel assemblies with the highest reserve reactivity from the spent fuel pool and place them in the center of the reactor; Step c): Assembling the refueling assembly into the reactor.

[0005] Further, in a preferred embodiment, steps a) to c) are repeated every 24 months.

[0006] Through the above method, the fuel cycle can be extended to 24 months, while the utilization rate of fuel in the reactor can be improved, effectively improving the economy of the nuclear power plant and reducing the operating costs of the nuclear power plant.

[0007] Furthermore, in some embodiments, in the replacement fuel assembly, at least some of the fuel rods include a burnable poison containing Gd.

[0008] Furthermore, in some embodiments, in the step c), a plurality of the fuel assemblies with the lowest remaining reserve reactivity in the refueling group are arranged at the periphery of the reactor core.

[0009] According to the design limits and safety certification conditions of the reactor, the feasible installation sequence of the refueling group is calculated and determined, and the refueling group is installed according to the installation sequence.

[0010] Furthermore, in some embodiments, the reactor includes 157 fuel assemblies.

[0011] Furthermore, in some embodiments, in the step a), 5.8%≤the first enrichment≤6%, 6.2%≤the second enrichment≤6.4%, and 6.5%≤the third enrichment≤6.7%.

[0012] Furthermore, in some embodiments, in the step b), a=8, b=40, and c=20.

[0013] Furthermore, in some embodiments, starting from the second fuel replacement, among the fuel assemblies put into the spent fuel pool in step b), 20 groups of the fuel assemblies undergo 3 fuel cycles, and 48 groups of the fuel assemblies undergo 2 fuel cycles.

[0014] Furthermore, in some embodiments, in the step b), among the replacement fuel assemblies in the refueling group, there are 20 groups of the fuel assemblies, each of which includes 16 fuel rods containing Gd burnable poison; there are 20 groups of the fuel assemblies, each of which includes 28 fuel rods containing Gd burnable poison; and there are 28 groups of the fuel assemblies, each of which includes 36 fuel rods containing Gd burnable poison.

[0015] Furthermore, in some embodiments, the equilibrium cycle life of the fuel assembly in the reactor is not less than 680 equivalent full power days. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of a partial layout of a balanced cycle core in an embodiment; Figure 2 A schematic diagram of a fuel assembly including 16 fuel rods containing Gd burnable poison in one embodiment; Figure 3A schematic diagram of a fuel assembly including 28 fuel rods containing Gd burnable poison in one embodiment; Figure 4 FIG. 1 is a schematic diagram of a fuel assembly including 36 Gd-containing burnable poison fuel rods in one embodiment.

[0017] 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 it is not intended to limit the present invention. For the sake of simplicity, the above drawings do not strictly draw the complete structure and all details according to the actual scale. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0019] 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.

[0020] 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.

[0021] Core fuel management is one of the important aspects of nuclear power plant core design. Its main tasks are to determine the enrichment of fuel assemblies, the distribution of the enrichment of fuel rods in the assemblies, and the loading and refueling methods of fuel assemblies with different enrichments in the core, and to select the type of burnable poisons and their arrangement in the core, so as to provide a core fuel management strategy that meets the overall design requirements and is more economical. The quality of core fuel management directly affects the economy and safety of nuclear power plant operation.

[0022] The high economy brought by long-cycle, high-burnup fuel management technology to nuclear power plant operation has always been of great concern to nuclear power plant owners, and is also a key technology to further improve the competitiveness of nuclear power. With the continuous increase in the number of nuclear power units in operation in China, the demand for longer-cycle (24-month) fuel management methods in nuclear power plants is gradually increasing. At present, the domestic passive nuclear power plants in operation mainly adopt an 18-month fuel management strategy, and the nominal enrichment of the fuel has approached or reached 4.95%, and the enrichment and burnup have approached or reached the limit.

[0023] The shortcomings of the current 18-month refueling cycle fuel management method are: 1) In order to meet the capacity requirements of nuclear power plants in winter heating or summer peak power supply scenarios, nuclear power plants usually use extended operation or extended refueling cycles to adjust the cycle length. Limited by the fuel enrichment limit and fuel rod burnup limit, the number of refueling components needs to be further increased, which will lead to a low fuel utilization rate for the long-cycle refueling strategy; 2) Limited by the current fuel enrichment and fuel rod burnup limits, it will be difficult to achieve a longer cycle refueling target quickly, and the operational safety and operational flexibility of nuclear power plants will be subject to certain restrictions. In summary, the traditional 18-month fixed refueling cycle model has been unable to meet the economic production needs of nuclear power plants. There is still room for further optimization of the operating economy of nuclear power plants.

[0024] At present, commercial nuclear power plants represented by AP1000 reactors generally use passive pressurized water reactors consisting of 157 fuel assemblies. Under the current fuel management method, fuel rods with a maximum enrichment of 4.95% are used, the refueling cycle is 18 months, 64 new fuel assemblies are loaded in each cycle, and the maximum fuel rod burnup does not exceed 62000MWd / tU. If the current fuel design is used, if the refueling cycle is extended to 24 months, the number of new fuel assemblies loaded in the balance cycle needs to reach 96, which exceeds half of the total number of core fuel assemblies. This means that 36 of the fuel assemblies are unloaded after only one fuel cycle in the core, which leads to low fuel utilization and low economic efficiency of nuclear power plant operation.

[0025] Since the Fukushima nuclear accident, the international nuclear industry has invested a lot of resources in the research and development of accident-tolerant fuel (ATF) technology. ATF technology, represented by chromium-coated zirconium alloy cladding and doped large-grain pellets, has gradually matured and is ready for large-scale commercial applications. With the new ATF technology, the average fuel consumption of the support rods can exceed the limit of 62,000 MWd / tU in terms of fuel performance. In addition, when the fuel enrichment is increased to more than 5%, it is expected to achieve a more economical 24-month refueling cycle fuel management strategy. The increase in the fuel consumption limit and the realization of a 24-month refueling cycle will greatly save the overhaul costs of the unit throughout its life cycle, reduce the output of spent fuel and save the cost of spent fuel treatment. It also balances the increase in ATF research and development costs and manufacturing costs, and has considerable commercial prospects.

[0026] The embodiment of the present invention provides a long-cycle fuel management method based on accident-tolerant fuel, which extends the fuel replacement cycle to 24 months on the basis of achieving full utilization of fuel, effectively improving the economy of nuclear power plants.

[0027] Specifically, the method comprises the following steps: Step a): Provide a fuel assembly for replacement. The fuel rods in the replacement fuel assembly use accident-tolerant fuels, and the enrichment of these accident-tolerant fuels is above 5%. In order to achieve a balanced cycle, fuels with three different enrichments are provided, wherein 5%<first enrichment<second enrichment<third enrichment. In a preferred embodiment, 5.8%≤first enrichment≤6%, 6.2%≤second enrichment≤6.4%, and 6.5%≤third enrichment≤6.7%. In a further preferred embodiment, at least part of the fuel rods in the replacement fuel assembly use Gd-containing combustible poisons, and the Gd-containing combustible poisons are arranged and loaded along the axial portion of the length of the fuel rods to optimize the axial power distribution throughout the cycle.

[0028] Step b): When refueling, take out n groups of fuel assemblies in the reactor that have undergone at least two fuel cycles and put them into a spent fuel pool, wherein n is not less than 1 / 3 and not more than 1 / 2 of the total number of fuel assemblies in the reactor; select group a replacement fuel assemblies with a first enrichment, group b replacement fuel assemblies with a second enrichment, and group c replacement fuel assemblies with a third enrichment, wherein a+b+c=n-1, and mix these replacement fuel assemblies with the remaining fuel assemblies in the reactor as a refueling group; select a group of fuel assemblies with the highest remaining reserve reactivity from the spent fuel pool, and use these fuel assemblies as the fuel assemblies in the center of the reactor after refueling.

[0029] Step c): Based on the design limits and safety certification conditions of the reactor, calculate and determine a feasible installation sequence for the fuel replacement group in the reactor that can meet the power leveling and safe operation conditions, and arrange the fuel replacement group according to the installation sequence. It should be understood that the specific form of the installation sequence is not unique. In a preferred embodiment, the final installation sequence adopted should arrange multiple fuel assemblies with the lowest remaining backup reactivity on the periphery of the reactor core, using a low-leakage loading method to reduce the neutron irradiation dose to the pressure vessel and improve economic efficiency. It should be understood that the low-leakage loading method should also meet power leveling and other safety design requirements. If Figure 1 As shown, except for H2, the fuel assemblies that have undergone two cycles are all placed at the outermost periphery, and all newly loaded fuel assemblies are not at the outermost periphery.

[0030] Step d): Repeat steps a) to c) every 24 months to enter the next fuel cycle. In some embodiments, the fuel replacement cycle can also be set to a length between 18 months and 24 months according to actual conditions.

[0031] In a preferred embodiment, for an AP1000 pressurized water reactor having 157 fuel assemblies in the reactor core, the long-cycle fuel management method based on accident-tolerant fuel has the following steps: Step a): providing a replacement fuel assembly, wherein the replacement fuel assembly uses accident-tolerant fuel with three different enrichments, and the fuel enrichments are 5.9%, 6.3% and 6.6% respectively.

[0032] Step b): 69 fuel assemblies that have undergone at least two fuel cycles are unloaded from the core and put into the spent fuel pool. 8 replacement fuel assemblies with an enrichment of 5.9%, 40 replacement fuel assemblies with an enrichment of 6.3%, and 20 fuel assemblies with an enrichment of 6.6% are provided to form a refueling group together with the remaining fuel assemblies in the reactor. A group of old fuel assemblies with the highest reserve reactivity are selected from the spent fuel pool as the fuel assemblies to be set in the center of the reactor core.

[0033] Step c): According to the design limit and safety certification conditions of the reactor, calculate and determine the installation sequence of the refueling group that meets the certification requirements in the core after refueling. The installation sequence should meet the power flattening conditions and safety design requirements. Furthermore, in order to reduce core leakage, improve economic efficiency, and reduce the neutron irradiation dose received by the pressure vessel, select Figure 1 As shown ( Figure 1 The FEED mark means the newly loaded fuel assembly, and the remaining fuel assembly with the lowest reserve reactivity among the original fuel assemblies in the core is arranged on the periphery of the reactor core (on the basis of meeting the design limits and safety certification conditions).

[0034] It should be understood that Figure 1 The arrangement shown is not exclusive, and those skilled in the art can calculate other installation sequence forms that meet the requirements based on the reactor design and operation requirements.

[0035] Step d): Step b) and step c are repeated every 24 months. Under this cycle mode, of the 68 new fuel assemblies added to the reactor, 20 fuel assemblies undergo 3 fuel cycles in the core, and 48 fuel assemblies undergo 2 fuel cycles in the core. The balanced cycle life of the fuel assemblies in the core can reach 682 equivalent full-power days, achieving a 24-month long-cycle fuel replacement.

[0036] Furthermore, in the 24-month refueling balance cycle, the reserve reactivity at the beginning of the core life is high and the power factor peak is also high. Therefore, some of the fuel rods in the partial replacement fuel assemblies are equipped with Gd-containing burnable poison to reduce the core boron concentration at the beginning of the life to prevent excessive boron concentration from causing positive moderator temperature feedback and to flatten the core power distribution. The distribution of fuel assemblies using Gd-containing burnable poison and the number of Gd-containing fuel rods therein are shown in Figure 1As shown in the figure (the fuel assemblies that have experienced one or more cycles in the core are considered to have completely consumed the burnable poison), the Gd burnable poison is loaded in the axial direction using a partial length to optimize the axial power distribution state in the entire cycle. In step b), the 68 groups of newly loaded fuel assemblies contain a total of 1,888 Gd burnable poison fuel rods, which are distributed as follows: 20 groups of fuel assemblies are loaded as follows Figure 2 The loading method shown is equipped with 16 fuel rods containing Gd burnable poison; 20 fuel assemblies are equipped with Figure 3 The loading method shown is equipped with 28 fuel rods containing Gd burnable poison; 28 fuel assemblies are used as follows Figure 4 The loading arrangement shown carries 36 fuel rods containing Gd burnable poison.

[0037] It should be understood that Figure 2 , Figure 3 , Figure 4 The fuel assembly form shown is not the only limitation. Those skilled in the art can make flexible adjustments based on the specific parameters and service conditions of the fuel assembly. When the type, enrichment, and combustible poison used in the fuel change, the form of the fuel assembly should also be adaptively adjusted.

[0038] In the above embodiment, a long-cycle fuel management method based on accident-tolerant fuel is used, fuel with a fuel enrichment of more than 5% is used, the burnup limit is increased, and the number of new fuel assemblies in the balance cycle is minimized, thereby effectively achieving a long-cycle fuel management of 24 months.

[0039] Compared with the existing 24-month fuel management method with a maximum enrichment of no more than 5% and a maximum rod fuel consumption of no more than 62000MWd / tU, the fuel management method provided by the embodiment of the present invention reduces the number of new fuel assemblies in the balanced cycle by 29%, significantly improves fuel utilization, reduces the average annual overhaul cost of nuclear power plants, and improves the economic efficiency of nuclear power plant operation.

[0040] It should be understood that the fuel management method provided in the above implementation is not limited to the AP1000 reactor. For other types of reactors, the fuel management method provided by the present invention can also be used to calculate the corresponding fuel management method based on the specific parameters and operating characteristics of the reactor.

[0041] The purpose of the above embodiments is to further 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 long-term fuel management method based on accident-tolerant fuel, characterized in that: The following steps are involved: Step a): providing a replacement fuel assembly, wherein the replacement fuel assembly uses an accident-tolerant fuel, and the accident-tolerant fuel in the replacement fuel assembly has a first enrichment, a second enrichment, and a third enrichment, respectively, wherein 5%<first enrichment<second enrichment<third enrichment; Step b): Take out n groups of fuel assemblies in the reactor and put them into a spent fuel pool, wherein the fuel assemblies put into the spent fuel pool have undergone at least two fuel cycles, and n is not less than 1 / 3 and not more than 1 / 2 of the total number of fuel assemblies in the reactor; mix the replacement fuel assemblies of group a with a first enrichment, group b with a second enrichment, and group c with a third enrichment with the remaining fuel assemblies in the reactor to obtain a replacement group, wherein a+b+c=n-1; take out a group of fuel assemblies with the highest reserve reactivity from the spent fuel pool and place them in the center of the reactor; Step c): Assembling the refueling assembly into the reactor.

2. The long-cycle fuel management method based on accident-tolerant fuel according to claim 1 is characterized in that: Also includes: Step d): Repeat steps a) to c) every 24 months.

3. The long-term fuel management method based on accident-tolerant fuel according to claim 1 is characterized in that: In the replacement fuel assembly, at least part of the fuel rods include a burnable poison containing Gd.

4. The long-cycle fuel management method based on accident-tolerant fuel according to claim 1, 2 or 3, characterized in that: In the step c), a plurality of the fuel assemblies with the lowest remaining reserve reactivity in the refueling group are arranged at the periphery of the reactor core.

5. The long-cycle fuel management method based on accident-tolerant fuel according to claim 1, 2 or 3, characterized in that: The reactor includes 157 fuel assemblies.

6. The long-term fuel management method based on accident-tolerant fuel according to claim 5 is characterized in that: In the step a), 5.8%≤the first enrichment≤6%, 6.2%≤the second enrichment≤6.4%, and 6.5%≤the third enrichment≤6.7%.

7. The long-term fuel management method based on accident-tolerant fuel according to claim 6 is characterized in that: In the step b), a=8, b=40, c=20.

8. The long-term fuel management method based on accident-tolerant fuel according to claim 7 is characterized in that: Starting from the second fuel replacement, among the fuel assemblies put into the spent fuel pool in step b), 20 groups of the fuel assemblies experienced 3 fuel cycles, and 48 groups of the fuel assemblies experienced 2 fuel cycles.

9. The long-term fuel management method based on accident-tolerant fuel according to claim 7, characterized in that: In the step b), among the replacement fuel assemblies in the refueling group, there are 20 groups of the fuel assemblies, each of which includes 16 fuel rods containing Gd burnable poison; there are 20 groups of the fuel assemblies, each of which includes 28 fuel rods containing Gd burnable poison; and there are 28 groups of the fuel assemblies, each of which includes 36 fuel rods containing Gd burnable poison.

10. The long-term fuel management method based on accident-tolerant fuel according to claim 7, characterized in that: The equilibrium cycle life of the fuel assembly in the reactor is not less than 680 equivalent full-power days.

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