A long-term fuel management method based on accident tolerant fuel

Abstract

A long-term fuel management method based on accident-tolerant fuel, comprising the following steps: providing replacement fuel assemblies with a first enrichment degree, a second enrichment degree, and a third enrichment degree, wherein 5% < the first enrichment degree < the second enrichment degree < the third enrichment degree, and the replacement fuel assemblies adopt accident-tolerant fuel; taking out 69 groups of fuel assemblies in the reactor and putting them into the spent fuel pool, selecting a group of fuel assemblies with the highest reserve reactivity from the spent fuel pool and setting it at the center of the reactor, and taking 68 groups of replacement fuel assemblies and the remaining fuel assemblies in the reactor as a refueling group; calculating the installation sequence of the refueling group according to the reactor design limit and safety certification conditions and installing it; repeating refueling every 24 months. This method can extend the fuel cycle period to 24 months, effectively improve the fuel utilization rate, and improve the economy of nuclear power plants.

Description

Technical Field

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

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

[0003] The purpose of the present invention is to provide a long-term fuel management method based on accident-tolerant fuel to improve the operating economy of nuclear power plants.

[0004] According to an embodiment of the present invention, a long-term fuel management method based on accident-tolerant fuel is provided, and the method includes the following steps:

[0005] Step a): Provide replacement fuel assemblies, the replacement fuel assemblies adopt accident-tolerant fuel, and the accident-tolerant fuel in the replacement fuel assemblies has a first enrichment, a second enrichment, and a third enrichment respectively, where 5% < the first enrichment < the second enrichment < the third enrichment;

[0006] Step b): Take out n groups of fuel assemblies in the reactor and put them into the spent fuel pool, where the fuel assemblies put into the spent fuel pool have experienced at least two fuel cycles, n is not less than 1 / 3 of the total number of fuel assemblies in the reactor and not more than 1 / 2; Mix a groups of the replacement fuel assemblies with the first enrichment, b groups of the replacement fuel assemblies with the second enrichment, and c groups of the replacement fuel assemblies with the third enrichment with the remaining fuel assemblies in the reactor to obtain a refueling group, where a + b + c = n - 1, and take out the group of fuel assemblies with the highest backup reactivity from the spent fuel pool and set it at the center of the reactor;

[0007] Step c): Load the refueling group into the reactor.

[0008] Further, in a preferred embodiment, steps a) to c) are repeated every 24 months.

[0009] By the above method, the fuel cycle period can be extended to 24 months, while improving the utilization rate of fuel in the reactor, effectively improving the economy of the nuclear power plant, and reducing the operation cost of the nuclear power plant.

[0010] Further, in some embodiments, in the replacement fuel assembly, at least some of the fuel rods include Gd burnable poisons.

[0011] Further, in some embodiments, in step c), a plurality of the fuel assemblies with the lowest remaining excess reactivity in the refueling group are arranged on the periphery of the reactor core.

[0012] According to the design limits and safety certification conditions of the reactor, calculate and determine the feasible installation sequence of the refueling group, and install the refueling group according to the installation sequence.

[0013] Further, in some embodiments, the reactor includes 157 fuel assemblies.

[0014] Further, in some embodiments, in step a), 5.8% ≤ the first enrichment degree ≤ 6%, 6.2% ≤ the second enrichment degree ≤ 6.4%, 6.5% ≤ the third enrichment degree ≤ 6.7%.

[0015] Further, in some embodiments, in step b), a = 8, b = 40, c = 20.

[0016] Further, 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 experience 3 fuel cycles, and 48 groups of fuel assemblies experience 2 fuel cycles.

[0017] Further, in some embodiments, in step b), among the replacement fuel assemblies in the refueling group, 20 groups of the fuel assemblies each include 16 fuel rods containing Gd burnable poisons; 20 groups of the fuel assemblies each include 28 fuel rods containing Gd burnable poisons; 28 groups of the fuel assemblies each include 36 fuel rods containing Gd burnable poisons.

[0018] Further, in some embodiments, the equilibrium cycle life of the fuel assemblies in the reactor is not less than 680 equivalent full power days. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the partial layout of the equilibrium cycle core in an embodiment;

[0020] Figure 2 It is a schematic diagram of a fuel assembly including 16 fuel rods containing Gd burnable poisons in an embodiment;

[0021] Figure 3 Schematic diagram of a fuel assembly including 28 Gd-containing burnable poison fuel rods in one embodiment;

[0022] Figure 4 Schematic diagram of a fuel assembly including 36 Gd-containing burnable poison fuel rods in one embodiment.

[0023] The purpose of the above drawings is to illustrate the present invention in detail 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 do not strictly draw the complete structure and all details in actual proportion. Specific Embodiments

[0024] The present invention will be further described in detail below through specific embodiments in conjunction with the drawings.

[0025] 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.

[0026] 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.

[0027] Core fuel management is one of the important contents of the core design of a nuclear power plant. Its main task is 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 poison and its arrangement in the core, etc., 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 the operation of a nuclear power plant.

[0028] The high economy brought by the fuel management technology with a long cycle and high burnup to the operation of a nuclear power plant has always been highly concerned by the owners of nuclear power plants, and it is also a key technology to further improve the competitiveness of nuclear power. With the continuous increase in the number of operating nuclear power units in China, the demand of nuclear power plants for fuel management methods with a longer cycle (24 months) is gradually increasing. At present, the passive nuclear power plants in operation in China 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 values.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] Specifically, the method comprises the following steps:

[0034] Step a): Provide a fuel assembly for replacement. The fuel rods in the replacement fuel assembly adopt 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, where 5% < the first enrichment < the second enrichment < the third enrichment. In a preferred embodiment, 5.8% ≤ the first enrichment ≤ 6%, 6.2% ≤ the second enrichment ≤ 6.4%, and 6.5% ≤ the third enrichment ≤ 6.7%. In a further preferred embodiment, at least some of the fuel rods in the replacement fuel assembly adopt Gd-containing burnable poisons, and the Gd-containing burnable poisons are loaded in a partial length arrangement along the axial direction of the fuel rod to optimize the axial power distribution throughout the cycle.

[0035] Step b): During refueling, take out n groups of fuel assemblies in the reactor that have experienced at least two fuel cycles and put them into the spent fuel pool, where n is not less than 1 / 3 and not more than 1 / 2 of the total number of fuel assemblies in the reactor; select a group of replacement fuel assemblies with the first enrichment, b group of replacement fuel assemblies with the second enrichment, and c group of replacement fuel assemblies with the third enrichment, where a + b + c = n - 1, and mix these replacement fuel assemblies with the remaining fuel assemblies in the reactor as the refueling group; select the group of fuel assemblies with the highest remaining excess reactivity from the spent fuel pool and use this fuel assembly as the fuel assembly at the center of the reactor after refueling.

[0036] Step c): According to the design limits and safety certification conditions of the reactor, calculate and determine a feasible installation sequence for the refueling group in the reactor that can meet the power flattening and safe operation conditions, and arrange the refueling group according to this installation sequence. It should be understood that the specific form of the installation sequence is not unique. In a preferred embodiment, the finally adopted installation sequence should arrange multiple fuel assemblies with the lowest remaining excess reactivity at the periphery of the reactor core to reduce the neutron irradiation dose received by the pressure vessel in a low-leakage loading manner and improve the economy. It should be understood that the low-leakage loading manner should also meet the power flattening and other safety design requirements. As Figure 1 shown, fuel assemblies that have experienced 2 cycle periods except H2 are all arranged at the outermost periphery, and all newly loaded fuel assemblies are not at the outermost periphery.

[0037] Step d): Repeat steps a) to c) every 24 months to enter the next fuel cycle. In some embodiments, the refueling cycle can also be set to a certain length between 18 months and 24 months according to the actual situation.

[0038] In a preferred embodiment, for an AP1000 pressurized water reactor with 157 fuel assemblies arranged in the reactor core, the long-cycle fuel management method based on accident-tolerant fuels is as follows:

[0039] Step a): Provide a replacement fuel assembly. The replacement fuel assembly uses accident-tolerant fuel and has three different enrichments, with fuel enrichments of 5.9%, 6.3%, and 6.6% respectively.

[0040] Step b): Remove 69 groups of fuel assemblies that have experienced at least two fuel cycles from the core and place them in the spent fuel pool. Provide 8 groups of replacement fuel assemblies with an enrichment of 5.9%, 40 groups of replacement fuel assemblies with an enrichment of 6.3%, and 20 groups of fuel assemblies with an enrichment of 6.6%, and jointly form a refueling group with the remaining fuel assemblies in the reactor. Select the group of old fuel assemblies with the highest reserve reactivity from the spent fuel pool as the fuel assembly set at the center of the reactor core.

[0041] Step c): According to the design limits 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. The installation sequence should meet the power flattening condition and safety design requirements. Further, in order to reduce core leakage, improve economy, and reduce the neutron irradiation dose received by the pressure vessel, select the arrangement shown in Figure 1 ( Figure 1 is 1 / 4 of the core area, the fuel assembly H2 is at the center of the core, that is, the symmetry center of the core, and the connection line of H2-X3 is two symmetry axes. The other fuel assemblies on the connection line of H2-X3 except X3 are actually located inside the core), where the meaning of the FEED mark is the newly loaded fuel assembly, and the fuel assembly with the lowest remaining 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).

[0042] It should be understood that Figure 1 the arrangement shown is not the only one, and those skilled in the art can calculate other forms of installation sequences that meet the requirements according to the reactor design and operation requirements.

[0043] Step d): Repeat Step b) and Step c) every 24 months. In this cyclic mode, among the 68 groups of fuel assemblies newly loaded into the reactor each time, 20 groups of fuel assemblies experience 3 fuel cycles in the core, 48 groups of fuel assemblies experience 2 fuel cycles in the core, and the equilibrium cycle life of the fuel assemblies in the core can reach 682 equivalent full power days, realizing 24-month long-cycle refueling.

[0044] Further, in the equilibrium cycle of 24-month refueling, the reserve reactivity at the beginning of the core life is relatively high, and the peak value of the power factor is also relatively high. Therefore, some fuel rods in some replacement fuel assemblies use Gd-containing burnable poisons to reduce the core boron concentration at the beginning of the life to prevent excessive boron concentration from causing a positive moderator temperature feedback, and at the same time flatten the core power distribution. The distribution of the fuel assemblies using Gd-containing burnable poisons and the number of Gd-containing fuel rods in them are as shown in Figure 1As shown (it is considered that the burnable poison has been completely consumed in the fuel assemblies that have experienced one or more cycles in the core), the Gd burnable poison is axially loaded in partial lengths to optimize the axial power distribution state throughout the cycle. In step b), among the 68 newly loaded fuel assemblies, there are a total of 1,888 Gd burnable poison fuel rods, and their distribution is as follows: 20 fuel assemblies are loaded with 16 Gd burnable poison fuel rods in the loading manner shown in Figure 2 ; 20 fuel assemblies are loaded with 28 Gd burnable poison fuel rods in the loading manner shown in Figure 3 ; 28 fuel assemblies are loaded with 36 Gd burnable poison fuel rods in the loading manner shown in Figure 4 .

[0045] It should be understood that Figure 2 , Figure 3 , Figure 4 The forms of the fuel assemblies shown are not the only limitations. Those skilled in the art can make flexible adjustments according to the specific parameters and service conditions of the fuel assemblies. When the types of fuel, enrichment, and burnable poison change, the forms of the fuel assemblies should also be adjusted adaptively.

[0046] In the above embodiments, through the long-term fuel management method based on accident-tolerant fuel, fuels with an enrichment of more than 5% are utilized, the burnup limit is increased, and the number of newly loaded fuel assemblies in the balance cycle is minimized as much as possible, effectively achieving a 24-month long-term fuel management.

[0047] Compared with the existing 24-month fuel management method with a maximum enrichment of no more than 5% and a maximum rod burnup of no more than 62,000 MWd / tU, the number of newly loaded fuel assemblies in the balance cycle of the fuel management method provided by the embodiments of the present invention is reduced by 29%, the fuel utilization rate is significantly improved, the annual average overhaul cost of the nuclear power plant is reduced, and the economic efficiency of the operation of the nuclear power plant is enhanced.

[0048] It should be understood that the fuel management method provided in the above embodiments is not limited to the AP1000 type 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 according to the specific parameters and operating characteristics of the reactor.

[0049] The purpose of the above embodiments is to further elaborate on the present invention in conjunction with the 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 method steps 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 long-term fuel management method based on accident-tolerant fuel, characterized in that, The reactor includes 157 fuel assemblies and comprises the following steps: Step a): Provide replacement fuel assemblies, where the replacement fuel assemblies adopt accident-tolerant fuels. The accident-tolerant fuels in the replacement fuel assemblies have a first enrichment, a second enrichment, and a third enrichment respectively, where 5% < the first enrichment < the second enrichment < the third enrichment, 5.8% ≤ the first enrichment ≤ 6%, 6.2% ≤ the second enrichment ≤ 6.4%, and 6.5% ≤ the third enrichment ≤ 6.7%; in the replacement fuel assemblies, at least some of the fuel rods include Gd burnable poisons. Step b): Remove 69 groups of fuel assemblies from the reactor and put them into the spent fuel pool, where the fuel assemblies put into the spent fuel pool have experienced at least two fuel cycles; mix 8 groups of the replacement fuel assemblies with the first enrichment, 40 groups of the replacement fuel assemblies with the second enrichment, and 20 groups of the replacement fuel assemblies with the third enrichment with the remaining fuel assemblies in the reactor to obtain a refueling group. Take out the group of fuel assemblies with the highest reserve reactivity from the spent fuel pool and arrange it at the center of the reactor; among the replacement fuel assemblies in the refueling group, in 20 groups of the fuel assemblies, each group includes 16 fuel rods containing Gd burnable poisons; in 20 groups of the fuel assemblies, each group includes 28 fuel rods containing Gd burnable poisons; in 28 groups of the fuel assemblies, each group includes 36 fuel rods containing Gd burnable poisons. Step c): Load the refueling group into the reactor. Step d): Repeat steps a) to c) every 24 months. And 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 have experienced 3 fuel cycles, and 48 groups of fuel assemblies have experienced 2 fuel cycles.

2. The long-term fuel management method based on accident tolerant fuel according to claim 1, characterized in that, In step c), arrange the plurality of fuel assemblies with the lowest remaining reserve reactivity in the refueling group at the periphery of the reactor core.

3. The long-term fuel management method based on accident-tolerant fuel according to claim 1, wherein The equilibrium cycle life of the fuel assemblies in the reactor is not less than 680 equivalent full-power days.

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