Long cycle high burnup fuel management method

Abstract

Provided is a long-cycle high-burnup fuel management method, which comprises the following steps: S1. determining the number of fuel assemblies to be unloaded, wherein the fuel assemblies to be unloaded include a group of fuel assemblies located at the center of the core; S2. loading fuel assemblies, wherein the fuel assemblies include a group of old fuel assemblies that can be reused in the spent fuel pool and the remaining groups of brand-new fuel assemblies; S3. replacing the fuel assemblies located at the center of the core with the old fuel assemblies and loading brand-new fuel assemblies, so that the loaded fuel assemblies and the fuel assemblies that are not unloaded are in a chessboard distribution, the loaded new fuel assemblies are the same enrichment fuel assemblies or different enrichment fuel assemblies, and the enrichment of the new fuel assemblies is greater than 5%; and S4. repeating steps S1 to S3 at an interval of a 24-month refueling cycle. The above method significantly increases the cycle length on the basis of using fuel with a nuclear fuel enrichment of more than 5.0%, and achieves the long-cycle refueling target.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nuclear industry, in particular to the field of reactor core fuel management. BACKGROUND

[0002] Reactor core fuel management is one of the important contents of the design of the reactor core of a nuclear power plant. Its main task is to determine the enrichment of fuel assemblies, the distribution of enrichment of fuel rods in assemblies, and the loading and refueling mode of fuel assemblies with different enrichments in the reactor core, and to select the type of burnable poison and its arrangement in the reactor core, so as to provide a reactor core fuel management strategy that meets the overall design requirements and is more economical. The pros and cons of reactor core fuel management directly affect the economy and safety of the operation of a nuclear power plant.

[0003] Long-cycle, high-burnup fuel management technology can bring high economic value to the operation of a nuclear power plant. Such management technology has always been highly concerned by the owners of nuclear power plants and is a key factor in further improving the competitiveness of nuclear power. With the increasing number of nuclear power units in operation in China, the demand for longer-cycle fuel management methods such as 24 months is gradually increasing in nuclear power plants. At present, the non-power-driven nuclear power plants in operation in China mainly adopt an 18-month fuel management strategy, and the nominal enrichment of the fuel has reached or approached 4.95%, and the enrichment and burnup have reached or approached the limit.

[0004] The current 18-month refueling cycle fuel management method has the following shortcomings. 1) If a nuclear power plant needs to extend the operation and extend the refueling cycle, it will be limited by the fuel enrichment limit and the fuel rod burnup limit, and the number of refueling assemblies will need to be further increased, which will result in lower fuel utilization rate for long-cycle refueling strategies; 2) Limited by the current fuel enrichment and fuel rod burnup limits, it will be difficult to achieve the goal of longer refueling cycle, and the operation safety and flexibility of the nuclear power plant will be limited to a certain extent.

[0005] In summary, there is still room for further optimization of the fuel management scheme of a nuclear power plant. SUMMARY

[0006] An object of the present application is to provide a long-cycle, high-burnup fuel management method that significantly improves the cycle length of a nuclear power plant based on the use of fuel with a nuclear fuel enrichment of more than 5.0%, and achieves the goal of 24-month long-cycle refueling.

[0007] The long-cycle high-burnup fuel management method for achieving the above-mentioned purpose comprises the following steps: S1. determining the number of groups of unloaded fuel assemblies, including a group of fuel assemblies located at the center position of the reactor core; S2. loading fuel assemblies including a group of old fuel assemblies that can be reused in the spent fuel pool and the remaining groups of brand-new fuel assemblies; S3. replacing the fuel assemblies located at the center position of the reactor core with the old fuel assemblies and loading the brand-new fuel assemblies, so that the loaded fuel assemblies are distributed in a chessboard pattern with the unloaded fuel assemblies, the loaded brand-new fuel assemblies are the same enrichment fuel assemblies or different enrichment fuel assemblies, and the enrichment of the fuel assemblies is greater than 5%; and S4. repeating steps S1 to S3 at an interval of a 24-month refueling cycle.

[0008] In one or more embodiments, the fuel assemblies at the outermost position of the reactor core are the old fuel assemblies with the lowest backup reactivity.

[0009] In one or more embodiments, the number of loaded brand-new fuel assemblies is less than or equal to 1 / 2 of the total number of fuel assemblies in the reactor core.

[0010] In one or more embodiments, the fewer the number of loaded brand-new fuel assemblies, the higher the enrichment of the loaded brand-new fuel assemblies.

[0011] In one or more embodiments, the loaded fuel assemblies simultaneously include integral burnable poisons and discrete water-passing ring-shaped burnable poisons.

[0012] In one or more embodiments, each fuel assembly in the reactor core is unloaded after the reactor core undergoes 2 or 3 cycles.

[0013] In one or more embodiments, in step S3, the loaded brand-new fuel assemblies are not arranged at the original positions of the unloaded fuel assemblies, and the unloaded fuel assemblies are replaced.

[0014] In one or more embodiments, the fuel assemblies use accident-tolerant fuel.

[0015] In one or more embodiments, the total number of fuel assemblies in the reactor core is 193, the number of groups of unloaded fuel assemblies is 97, including a group of fuel assemblies located at the center position of the reactor core and the remaining 96 groups of fuel assemblies, the fuel assemblies located at the center position of the reactor core are replaced with old fuel assemblies that can be reused in the spent fuel pool, and the 96 groups of fuel assemblies are replaced with brand-new fuel assemblies with an enrichment of 5.5%.

[0016] In one or more embodiments, the total number of fuel assemblies in the core is 193, the number of assemblies unloaded is 89, including one assembly located in the center of the core and the remaining 88 assemblies, the 88 assemblies including 16 assemblies of 5.7% enrichment that have undergone three cycles, 36 assemblies of 5.7% enrichment that have undergone two cycles, and 36 assemblies of 6.2% enrichment that have undergone two cycles; the assembly located in the center of the core is replaced with an old assembly from the spent fuel pool that can be recycled, and the 88 assemblies are replaced with 52 assemblies of 5.7% fresh fuel assemblies and 36 assemblies of 6.2% fresh fuel assemblies.

[0017] In one or more embodiments, the total number of fuel assemblies in the core is 193, the number of assemblies unloaded is 77, including one assembly located in the center of the core and the remaining 76 assemblies, the remaining 76 assemblies including 12 assemblies of 5.8% enrichment that have undergone three cycles, 4 assemblies of 6.1% enrichment that have undergone three cycles, 24 assemblies of 6.5% enrichment that have undergone three cycles, 4 assemblies of 5.8% enrichment that have undergone two cycles, 24 assemblies of 6.1% enrichment that have undergone two cycles, and 8 assemblies of 6.5% enrichment that have undergone two cycles; the assembly located in the center of the core is replaced with an old assembly from the spent fuel pool that can be recycled, and the 76 assemblies are replaced with 16 assemblies of 5.8% fresh fuel assemblies, 28 assemblies of 6.1% fresh fuel assemblies, and 32 assemblies of 6.5% fresh fuel assemblies.

[0018] The long-cycle high-burnup fuel management method described above uses accident-tolerant fuel, which allows the fuel enrichment to exceed 5.0%, thereby achieving a long-cycle fuel management scheme on the basis of improving the burnup limit, balancing the cycle life to 670 to 710 equivalent full-power days, achieving a 24-month long-cycle refueling design goal, increasing the discharged burnup, optimizing the core design, and significantly improving the economic efficiency and flexibility of the nuclear power plant, which can further improve the safety of the nuclear power plant. BRIEF DESCRIPTION OF DRAWINGS

[0019] The above and other features, properties, and advantages of the present application will become more apparent by describing in detail the following embodiments with reference to the accompanying drawings, in which:

[0020] Figure 1 is a balanced cycle core layout of the first embodiment;

[0021] Figure 2 is a balanced cycle core layout of the second embodiment;

[0022] Figure 3 is a balanced cycle core layout for the third embodiment;

[0023] Figure 4 is a schematic illustration of a fuel assembly distribution structure for 128 monolithic burnable poison fuel rods;

[0024] Figure 5 is a schematic illustration of a fuel assembly distribution structure for 156 monolithic burnable poison fuel rods;

[0025] Figure 6 is a schematic illustration of a fuel assembly distribution structure for 200 monolithic burnable poison fuel rods;

[0026] Figure 7 is a schematic illustration of a fuel assembly distribution structure for 156 monolithic burnable poison fuel rods and 8 discrete water bypass annular burnable poison rods;

[0027] Figure 8 is a schematic illustration of a fuel assembly distribution structure for 200 monolithic burnable poison fuel rods and 8 discrete water bypass annular burnable poison rods;

[0028] Figure 9 is a schematic illustration of a fuel assembly distribution structure for 156 monolithic burnable poison fuel rods and 16 discrete water bypass annular burnable poison rods;

[0029] Figure 10 is a schematic illustration of a fuel assembly distribution structure for 200 monolithic burnable poison fuel rods and 16 discrete water bypass annular burnable poison rods;

[0030] Figure 11 is a flowchart of a long cycle high burnup fuel management method. DETAILED DESCRIPTION

[0031] The present application is further described in the following description with reference to the figures in which embodiments of the application are illustrated by way of example. Like reference numerals may

[0032] It should be noted that these and other attached figures are merely schematic and are not drawn to scale, and that the specific dimensions, locations and other details are intended to be illustrative only and not limiting of the scope of the application as claimed.

[0033] Since the Fukushima nuclear accident in 2011, the international nuclear industry has invested heavily in the research and development of Accident Tolerant Fuel (ATF) technology. After more than a decade of effort, ATF technology, represented by chromium-coated zirconium alloy cladding and doped large-grain fuel pellets, has gradually matured and is ready for large-scale commercial application. Utilizing this new ATF technology, fuel performance can support an average fuel burnup exceeding the limit of 62,000 MWd / tU. Furthermore, with fuel enrichment increased to over 5%, a more economical 24-month refueling cycle fuel management strategy is expected to be achieved. The increased burnup limit and the realization of a 24-month refueling cycle will significantly reduce overhaul costs throughout the unit's lifespan, reduce spent fuel production and save on spent fuel processing costs, and also offset the increased R&D and manufacturing costs of ATF, demonstrating considerable commercial potential.

[0034] This disclosed method for managing fuel with a long-cycle, high burnup is a method for managing fuel with a nuclear fuel enrichment exceeding 5.0% and a long cycle of 24 months. Specifically, it includes the following steps: S1. Determine the number of fuel assembly groups to be removed, including one group located at the core center; S2. Load the fuel assemblies, including one group of reusable old fuel assemblies from the spent fuel pool and the remaining groups of brand-new fuel assemblies; S3. Replace the fuel assembly located at the core center with the old fuel assemblies and load brand-new fuel assemblies, so that the loaded fuel assemblies and the unremoved fuel assemblies are distributed in a checkerboard pattern. The loaded new fuel assemblies are either fuel assemblies of the same enrichment level or a collection of fuel assemblies of different enrichment levels, and the enrichment level of the fuel assemblies is greater than 5%; S4. Repeat steps S1 to S3 at 24-month refueling cycle intervals.

[0035] Preferably, in step S3, the newly installed fuel assemblies are not directly placed in the original position of the removed fuel assemblies. Instead, the remaining fuel assemblies are repositioned, meaning they also need to be moved from their original positions. Ultimately, the newly installed fuel assemblies and the remaining fuel assemblies are arranged in a checkerboard pattern. A checkerboard pattern means that the fuel assemblies are placed in a grid-like area, which includes multiple adjacent grid-like areas. In these adjacent grid-like areas, at least one grid-like area has the opposite newness / oldness attribute to the fuel assemblies within that area. For example... Figure 1 In the grid, the grid area is a square grid. If the fuel component in a square grid is a brand new fuel component, then at least one of the four adjacent grid areas of the square grid contains a used fuel component.

[0036] The following describes three specific embodiments and their corresponding appendices. Figures 1 to 3 This disclosure introduces the long-cycle, high-fuel-consumption fuel management method described herein. (Appendix) Figures 1-3The three groups of data from top to bottom in each box represent the zone number of the fuel assembly, the number of fuel element surface boron poison (IFBA) / discrete water passing annular combustible poison rod (WABA), and the number of cycles experienced by the fuel assembly, respectively. Each group of fuel assemblies in the core is discharged after 2 or 3 cycles experienced by the core.

[0037] First embodiment

[0038] The total number of fuel assemblies in the passive nuclear power plant is 193, and the new fuel assemblies use the same fuel enrichment of 5.5%. Half of the fuel assemblies are refueled, i.e. 96 new fuel assemblies are newly loaded into the core. In this embodiment, the fuel to be replaced includes 1 fuel assembly located at the center of the core and 96 fuel assemblies at other positions. Preferably, the 96 fuel assemblies to be discharged are the fuel assemblies with the lowest backup reactivity among all fuel assemblies.

[0039] The 1 fuel assembly at the center of the core is replaced by 1 old fuel assembly with higher backup reactivity in the spent fuel pool, which can effectively flatten the power distribution near the center of the core and improve fuel utilization.

[0040] The corresponding number of fuel assemblies are replaced by 96 new fuel assemblies with a fuel enrichment of 5.5%.

[0041] The 96 new fuel assemblies are arranged in the core as a whole in the zones, and the old fuel assemblies are arranged as a whole in a chessboard pattern, as shown in Figure 1 The white blocks are new fuel assemblies, and the gray blocks are fuel assemblies that have experienced one cycle.

[0042] The balanced cycle of the 24-month refueling period makes the backup reactivity higher at the beginning of the core life, and the power peak factor is also higher.

[0043] The new fuel assemblies to be loaded will use both bulk combustible poisons and discrete water passing annular combustible poisons, which can reduce the boron concentration in the core at the beginning of the life to prevent a positive moderator temperature feedback caused by excessively high boron concentration, and also help to flatten the core power distribution.

[0044] The number of fuel rods containing bulk combustible poison fuel rods in the new fuel assemblies is 128, 156, and 200, respectively, and the corresponding number of assemblies is 12, 20, and 64, respectively, i.e. 96 fuel assemblies. The combination of the above assemblies can flatten the power of the core, and is the optimal solution under the conditions of meeting the safety limit requirements, higher economy, and other factors for a 24-month refueling period.

[0045] The number of discrete water passing annular combustible poison rods in the new fuel assemblies is 8, and the corresponding number of assemblies is 44, which can also contain bulk combustible poison fuel rods.

[0046] The arrangement of burnable poison in the core can reduce the initial core boron concentration in the life cycle, on the one hand, to prevent the positive moderator temperature feedback caused by too high boron concentration, and on the other hand, to help flatten the core power distribution.

[0047] The least reactivity old fuel assemblies are arranged at the outermost of the core without being unloaded, to further reduce the core leakage, improve the economy, and reduce the neutron irradiation dose of the pressure vessel.

[0048] The first embodiment is directed to a passive nuclear power plant, which can achieve a 24-month refueling cycle cycle with enrichment exceeding 5.0%, improve the fuel rod burnup limit, reduce the number of new fuel assemblies, and overall improve the operation economy of the nuclear power plant.

[0049] Second embodiment

[0050] Independent of the first embodiment, the second embodiment provides a fuel management method for a passive nuclear power plant with higher fuel enrichment, a 24-month balanced cycle length, and a relatively smaller number of unloaded fuel assembly groups.

[0051] One group of fuel assemblies located at the center of the core is unloaded.

[0052] Eighty-eight groups of old fuel assemblies with the lowest reactivity are unloaded. The unloaded fuel assemblies include 16 groups of fuel assemblies with an enrichment of 5.7% that have experienced three cycles, 36 groups of fuel assemblies with an enrichment of 5.70% that have experienced two cycles, and 36 groups of fuel assemblies with an enrichment of 6.2% that have experienced two cycles.

[0053] The number of loaded refueling assemblies is 89 groups, including one group of old fuel assemblies with higher reactivity from the spent fuel pool that can be reused and 88 groups of new fuel assemblies. One group of old fuel assemblies from the spent fuel pool that can be reused is reused to replace the fuel assemblies located at the center of the core. The 88 groups of new fuel assemblies loaded include two different enrichments, 52 groups of new fuel assemblies with an enrichment of 5.7% and 36 groups of new fuel assemblies with an enrichment of 6.2%.

[0054] This scheme has better economy, while considering the need to meet the 24-month refueling cycle target, the fewer the number of new fuel assemblies loaded, the higher the enrichment of the new fuel assemblies loaded. As compared to the first embodiment, in the second embodiment, the 88 groups of fuel assemblies unloaded are less than the 96 groups unloaded in the first embodiment, and thus the combination of the enrichment of 5.7% and 6.2% of the new fuel assemblies used is higher than the enrichment of 5.5%.

[0055] The 88 groups of new fuel assemblies are arranged in the inner region of the core as a whole, and the old fuel assemblies are generally arranged in a chessboard pattern, as shown in Figure 2As shown, the white blocks are new fuel assemblies, the gray blocks are once- recycled fuel assemblies, and the grid blocks are twice-recycled fuel assemblies, located at the outermost side of the core.

[0056] In this way, the fuel utilization efficiency can be further improved by loading new fuel assemblies with different enrichment, and it helps to flatten the core power distribution. The above arrangement helps to reduce the core neutron leakage and improve the economy of the fuel management strategy.

[0057] 88The number of fuel rods containing monolithic burnable poison fuel rods in the new fuel assemblies is 128, 156, and 200, respectively, and the corresponding number of assemblies is 4, 24, and 60, respectively. The number of discrete water-cooled ring-shaped burnable poison rods in the new fuel assemblies is 16, and the corresponding number of assemblies is 64, which also contain monolithic burnable poison fuel rods.

[0058] The least-reactivity old fuel assemblies are arranged at the outermost side of the core without being unloaded, to further reduce the core leakage, improve the economy, and reduce the neutron irradiation dose of the pressure vessel.

[0059] The second embodiment is directed to a passive nuclear power plant, which realizes a 24-month refueling cycle with an enrichment exceeding 5.0%, and improves the fuel rod burnup limit, further reduces the number of new fuel assemblies compared to the first embodiment, and improves the overall operation economy of the nuclear power plant.

[0060] Third embodiment

[0061] Independent of the first and second embodiments, the third embodiment has a higher fuel enrichment than the first and second embodiments. The number of recycled refueling assemblies is 77, including 1 assembly of old fuel assemblies that can be reused from the spent fuel pool and 76 assemblies of new fuel assemblies.

[0062] One assembly of fuel assemblies at the center position is unloaded, and a set of available old fuel assemblies from the spent fuel pool is reused at this position.

[0063] Seventy-six assemblies of old fuel assemblies with the lowest reactivity are unloaded. The unloaded assemblies include 12 assemblies of fuel assemblies with an enrichment of 5.8% that have undergone three cycles, 4 assemblies of fuel assemblies with an enrichment of 6.1% that have undergone three cycles, 24 assemblies of fuel assemblies with an enrichment of 6.5% that have undergone three cycles, 4 assemblies of fuel assemblies with an enrichment of 5.8% that have undergone two cycles, 24 assemblies of fuel assemblies with an enrichment of 6.1% that have undergone two cycles, and 8 assemblies of fuel assemblies with an enrichment of 6.5% that have undergone two cycles, as shown in Figure 3 .

[0064] 76 new fuel assemblies contain three different enrichments, 16 new fuel assemblies with 5.8% enrichment, 28 new fuel assemblies with 6.1% enrichment and 32 new fuel assemblies with 6.5% enrichment.

[0065] 76 new fuel assemblies are arranged in the inner zone of the core as a whole, but not in the position to be unloaded, but are re-arranged together with the non-unloaded fuel assemblies, so that the non-unloaded fuel assemblies and the loaded new fuel assemblies are generally arranged in a chessboard pattern. In this way, by loading new fuel assemblies with different enrichments, the fuel utilization efficiency can be further improved, and the core power distribution can be flattened. The above arrangement helps to reduce the neutron leakage in the core and improve the economy of the fuel management strategy.

[0066] The number of fuel rods containing bulk burnable poison fuel rods in the new fuel assemblies is 156 and 200, respectively, and the corresponding number of assemblies is 20 and 56, respectively. The number of discrete water-passing ring-shaped burnable poison rods in the new fuel assemblies is 16, and the corresponding number of assemblies is 44, which also contain bulk burnable poison fuel rods. Arranging burnable poisons in the core can reduce the initial boron concentration in the core to prevent high boron concentration from causing positive moderator temperature feedback, and can also help to flatten the core power distribution.

[0067] The non-unloaded old fuel assemblies with the lowest reserve reactivity are arranged at the outermost side of the core to further reduce the core leakage, improve the economy, and reduce the neutron irradiation dose of the pressure vessel.

[0068] The above long-cycle high-burnup fuel management method uses accident-tolerant fuel, so that the fuel enrichment exceeds 5.0%, and the burnup limit is increased, and a long-cycle fuel management scheme of more than 18 months, up to 24 months, can be implemented. The use of bulk burnable poisons and discrete water-passing ring-shaped burnable poisons reduces the initial boron concentration in the core and flattens the core power distribution,

[0069] According to different refueling assembly numbers, such as half refueling, one-third refueling, etc., combined with different enrichments of new fuel assemblies, a variety of new fuel batches are used, such as a single enrichment (5.5%), two different enrichments (5.7% and 6.2%), three different enrichments (5.8%, 6.1% and 6.5%), etc., to realize different long-cycle fuel management strategies, balance the cycle life of 670 to 710 equivalent full-power days, and complete the long-cycle refueling design goal of 24 months, which can meet the different life length requirements of nuclear power plant extension operation and long-cycle refueling.

[0070] Although the present application is disclosed with reference to the preferred embodiments above, it is not intended to limit the present application, and any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present application. Therefore, any modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application without departing from the technical solutions of the present application, all fall within the protection scope defined by the claims of the present application.

Claims

1. A fuel management method for long-cycle, high-fuel-consumption periods, characterized in that, A loop including the following steps: S1. Determine the number of fuel assembly groups to be removed. Among the fuel assemblies to be removed is a group of fuel assemblies located at the center of the reactor core. S2. The loaded fuel assemblies include a set of old fuel assemblies that can be reused from the spent fuel pool and the remaining sets of brand new fuel assemblies; S3. Replace the fuel assembly located at the center of the reactor core with the old fuel assembly and load the new fuel assembly, so that the loaded fuel assembly and the unloaded fuel assembly are distributed in a checkerboard pattern. The loaded new fuel assembly is either a fuel assembly with the same enrichment level or a collection of fuel assemblies with different enrichment levels, and the enrichment level of the loaded fuel assembly is greater than 5%. The loaded new fuel assembly is not placed in the original position of the unloaded fuel assembly, and the unloaded fuel assembly is repositioned. S4. Repeat steps S1 to S3 at 24-month material change intervals; The fuel assembly uses fault-tolerant fuel; At least a portion of the fuel assemblies in the reactor core are removed after the core has undergone three cycles, the fuel assemblies including fuel assemblies that have undergone two cycles, fuel assemblies that have undergone one cycle, and new fuel assemblies. The fuel assemblies loaded include boron-coated poison and discrete water-permeable annular combustible poison rods; the outermost fuel assembly of the reactor core is the old fuel assembly with the lowest reactivity as a backup. The number of newly installed fuel assemblies is less than or equal to half the total number of fuel assemblies in the reactor core; The reactor core has a total of 193 fuel assemblies. 77 fuel assemblies were removed, including one fuel assembly located at the center of the core and 76 fuel assemblies in other locations. The remaining 76 fuel assemblies include 12 old fuel assemblies with an enrichment level of 5.8% that have undergone three cycles, 4 fuel assemblies with an enrichment level of 6.1% that have undergone three cycles, 24 fuel assemblies with an enrichment level of 6.5% that have undergone three cycles, 4 fuel assemblies with an enrichment level of 5.80% that have undergone two cycles, 24 fuel assemblies with an enrichment level of 6.1% that have undergone two cycles, and 8 fuel assemblies with an enrichment level of 6.5% that have undergone two cycles. The fuel assemblies located at the center of the reactor core were replaced with a set of reusable old fuel assemblies from the spent fuel pool, and 76 fuel assemblies were replaced with 16 sets of new fuel assemblies with an enrichment of 5.8%, 28 sets of new fuel assemblies with an enrichment of 6.1%, and 32 sets of new fuel assemblies with an enrichment of 6.5%.

2. The fuel management method for long-cycle, high-fuel-consumption operations as described in claim 1, characterized in that, The fewer the number of new fuel assemblies loaded, the higher the enrichment of the new fuel assemblies.

3. The fuel management method for long-cycle, high-fuel-consumption operations as described in claim 1, characterized in that, Each fuel assembly in the reactor core is removed after the core has undergone two or three cycles.

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