A fuel loading method for a pressurized water reactor core with a 24-month refueling cycle

Abstract

The present invention discloses a method for loading fuel in a 24-month refueling cycle for a pressurized water reactor core, characterized in that the pressurized water reactor core is composed of 177 fuel assemblies, the first cycle of the core adopts a 24-month refueling strategy, and each refueling of the core from the second cycle to the balance cycle adopts two new fuel assemblies with an enrichment of more than 5% U-235. The 24-month refueling strategy is adopted from the first cycle, and two new fuel assemblies with an enrichment of more than 5% U-235 are used for each refueling in the transition cycle and the balance cycle, so that the cycle lengths of the first cycle, transition cycle and balance cycle can be quickly achieved to meet the 24-month long-cycle refueling design requirements, reduce the average fuel cost, and increase the average batch unloading fuel consumption, which has extremely high economy.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear power plant reactors, and in particular to a method for loading fuel into a pressurized water reactor core during a 24-month refueling cycle. Background Art

[0002] At present, the mainstream cycle length of nuclear power plants in operation around the world, especially the pressurized water reactor nuclear power plants in East Asia, is about 18 months. For large nuclear power plants with increasingly higher power, due to the high line power density and enrichment limit, it is usually necessary to replace more than 1 / 2 of the core components each time to achieve a cycle length of 24 months, resulting in fuel economy indicators that are worse than 18-month refueling, so the 24-month refueling method has not been widely used.

[0003] At present, for the 24-month refueling core loading method, some people refuel 96 components each time (a total of 177 components in the core), and the average fuel cost is higher than the annual refueling and 18-month refueling. Some people refuel 116 components in 24 months (a total of 221 components in the core), and the average batch unloading fuel consumption is also lower than the 18-month scheme.

[0004] In summary, for large-scale nuclear power plants with high linear power density, the current 24-month core refueling loading method has a high average fuel cost, and the average batch unloading fuel consumption is also lower than the 18-month refueling cycle, resulting in lower economic efficiency. Summary of the invention

[0005] The technical problem to be solved by the present invention is that for large nuclear power plants of the million-kilowatt class, the existing 24-month refueling core loading method has high refueling cost and low average batch unloading fuel consumption, resulting in low economic efficiency and cannot be widely used. The purpose is to provide a 24-month refueling cycle fuel loading method for a pressurized water reactor core, using new fuel assemblies with an enrichment of more than 5% in transition cycles and balance cycles, and meeting the technical requirements of 24-month long-cycle refueling design for high-power nuclear power plants.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for loading fuel in a 24-month refueling cycle for a pressurized water reactor core, wherein the pressurized water reactor core is composed of 177 fuel assemblies, a 24-month refueling strategy is adopted for the first cycle of the core, and two new fuel assemblies with a U-235 enrichment exceeding 5% are used for each refueling in each cycle of the core from the second cycle to the balance cycle.

[0008] Optionally, the enrichment levels of the two new fuel assemblies with U-235 enrichment exceeding 5% are 5.45% and 5.95% respectively.

[0009] Optionally, 80 new fuel assemblies are loaded into the core each time the core is refueled from the second cycle to the balance cycle.

[0010] Optionally, the fuel assemblies of each cycle from the second cycle to the balance cycle are arranged in a low leakage mode, with the old fuel assemblies that have been burned deeply placed in the outermost circle of the core, and the new fuel assemblies and the old fuel assemblies that have been burned are placed in the inner circle of the core and arranged in a cross-spaced manner.

[0011] Optionally, the burned-up old fuel assemblies placed in the inner ring of the core are arranged in a cross pattern according to the burn-up depth.

[0012] Optionally, all circulating solid combustibles are integrated gadolinium solid combustibles in the form of gadolinium-loaded fuel rods, wherein the gadolinium-loaded fuel rods are formed by uniformly mixing UO2-Gd2O3 in fuel pellets;

[0013] The number of gadolinium-loaded fuel rods in the first cycle is 8, 12, 16 or 20;

[0014] The number of gadolinium-loaded fuel rods in each cycle from the second cycle to the balance cycle is 12, 16, 20 or 24.

[0015] Optionally, the U-235 enrichment in the UO2-Gd2O3 fuel pellets in each cycle from the second cycle to the equilibrium cycle is 2.5%, and the weight percentage of Gd2O3 is 10%.

[0016] Optionally, new fuel assemblies for the first cycle are loaded in four zones according to the enrichment of U-235. The enrichment of U-235 in the four zones are 3.1%, 3.9%, 4.45% and 4.95%, respectively. The new fuel assemblies with enrichment of U-235 of 3.1%, 3.9%, 4.45% and 4.95% are 69, 36, 36 and 36 groups respectively. The new fuel assemblies for the first cycle are arranged in a high leakage loading mode.

[0017] Optionally, the high leakage loading mode is: the new fuel assembly with the highest enrichment is placed in the outermost circle of the core, and the new fuel assemblies with other enrichments are combined with each other according to the enrichment degree.

[0018] Optionally, in the first cycle, the enrichment of U-235 in the UO2-Gd2O3 fuel pellets in the new fuel assemblies is 3.1%, 3.9%, 4.45% and 4.95%, the enrichment of U-235 in the UO2-Gd2O3 fuel pellets is 1.8%, 2.2%, 2.5% and 2.5% respectively, and the weight percentage of Gd2O3 in the UO2-Gd2O3 fuel pellets is 8%.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0020] The embodiment of the present invention provides a method for loading fuel for a pressurized water reactor core with a 24-month refueling cycle. The 24-month refueling strategy is adopted from the first cycle. Two new fuel assemblies with an enrichment of more than 5% U-235 are used in each refueling in the transition cycle and the balance cycle. The cycle lengths of the first cycle, transition cycle, and balance cycle can be quickly achieved to meet the 24-month long-cycle refueling design requirements, thereby reducing the average fuel cost and increasing the average batch unloading fuel consumption. The power plant availability after balancing is achieved to reach 92%; the average batch unloading fuel consumption of each batch of fuel assemblies after balancing is achieved to reach 58,000MWd / tU, which is about 10,000MWd / tU higher than the highest batch unloading fuel consumption of the 18-month fuel design of the same type of reactor. It can be applied to newly built power plants using 177 core groups and has extremely high economic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0022] Figure 1 A schematic diagram of loading a core of a first cycle of a pressurized water reactor core in a 24-month refueling cycle fuel loading method provided by an embodiment of the present invention;

[0023] Figure 2 A schematic diagram of loading a core of a second cycle of a pressurized water reactor core in a 24-month refueling cycle fuel loading method provided by an embodiment of the present invention;

[0024] Figure 3 A schematic diagram of loading a core of a third cycle of a method for loading fuel in a pressurized water reactor core for a 24-month refueling cycle provided by an embodiment of the present invention;

[0025] Figure 4 A schematic diagram of loading a balanced cycle core of a pressurized water reactor core with a 24-month refueling cycle fuel loading method provided in an embodiment of the present invention.

[0026] Among them, Figure 1 Each square in the figure represents a fuel assembly. The values ​​ZZZNN in each square mean: ZZZ / 100 represents the enrichment of the fuel assembly, and NN is the number of gadolinium rods in the fuel assembly. Taking 31008 as an example, it means that the fuel assembly at this position is a fuel assembly with an enrichment of 3.10% and 8 gadolinium rods.

[0027] Figure 2 Each square in the diagram represents a fuel assembly. The meanings are: m / 100 represents the enrichment of the fuel assembly, NEW represents the new fuel assembly placed here, and there are 80 new fuel assemblies in total, and the symbol n represents the number of gadolinium rods in the fuel assembly. The remaining squares such as M13, P11, etc. represent the old fuel assemblies that have been burned.

[0028] Figure 3 The squares in the squares and the squares in the squares The meaning of Figure 2 .

[0029] Figure 4 The values ​​in each square refer to the number of gadolinium-loaded fuel rods in each new fuel assembly. The underlined values ​​represent new fuel assemblies with 5.45% enrichment, and the others are new fuel assemblies with 5.95% enrichment. The squares with light shading are reusable fuel assemblies that have been burned up for one cycle, and the squares with dark shading are reusable fuel assemblies that have been burned up for two cycles. The squares without shading represent new fuel assemblies. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0031] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is apparent to one of ordinary skill in the art that these specific details are not necessarily employed to practice the present invention. In other embodiments, in order to avoid obscuring the present invention, well-known structures, circuits, materials, or methods are not specifically described.

[0032] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment," "an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. In addition, it will be appreciated by those of ordinary skill in the art that the figures provided herein are for illustrative purposes and that the figures are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0033] In the description of the present invention, the directions or positional relationships indicated by terms such as “front”, “rear”, “left”, “right”, “up”, “down”, “vertical”, “horizontal”, “high”, “low”, “inside” and “outside” are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the scope of protection of the present invention.

[0034] The existing 24-month core loading method for large-scale nuclear power plants with a capacity of one million kilowatts has an average fuel cost higher than annual and 18-month refueling, and the average batch unloading fuel consumption is also relatively low, which cannot meet the technical requirements of the 24-month long-cycle refueling design for high-power nuclear power plants.

[0035] To solve the above problems, the following technical solutions are adopted:

[0036] A method for loading fuel in a 24-month refueling cycle for a pressurized water reactor core, wherein the pressurized water reactor core is composed of 177 fuel assemblies, a 24-month refueling strategy is adopted for the first cycle of the core, and two new fuel assemblies with a U-235 enrichment exceeding 5% are used for each refueling in each cycle of the core from the second cycle to the balance cycle.

[0037] Among them, the embodiment of the present invention adopts a 24-month refueling strategy from the first cycle, and realizes 24-month refueling from the first cycle. In the transition cycle and the balance cycle, two new fuel assemblies with an enrichment of more than 5% U-235 are used for each refueling, so that the cycle lengths of the first cycle, transition cycle and balance cycle can be quickly achieved to meet the 24-month long-cycle refueling design requirements. The use of refueling assemblies with an enrichment of more than 5% can increase the residual reactivity of the initial core without significantly increasing the number of refueling assemblies, thereby achieving a longer cycle length. A longer cycle length and as few new refueling assemblies as possible can greatly increase the batch unloading burnup of the assemblies, bringing a series of benefits such as improving assembly utilization, reducing fuel costs, and reducing high-level waste. The enrichment of the two new fuel assemblies can be selected as 5.45% and 5.95% respectively.

[0038] Furthermore, each time the core is refueled from the second cycle to the balance cycle, 80 new fuel assemblies are loaded. The number of new fuel assemblies with two enrichment levels can be selected as needed. For example, the 80 new fuel assemblies include 4 new fuel assemblies with an enrichment level of 5.45% and 76 new fuel assemblies with an enrichment level of 5.95%.

[0039] Furthermore, the fuel assemblies of each cycle from the second cycle to the balance cycle are arranged in a low leakage mode, with the old fuel assemblies that have been burned deeply placed at the outermost circle of the core, and the new fuel assemblies and the old fuel assemblies that have been burned are placed at the inner circle of the core and arranged in a cross-spaced manner. The burnup degree of the old fuel assemblies that have been burned is also different.

[0040] Furthermore, the burned-up old fuel assemblies placed in the inner ring of the core are arranged in a cross pattern according to the burn-up depth.

[0041] By rationally arranging new and old fuel assemblies in the transition cycle and balance cycle and making rational use of reusable assemblies, extremely low leakage of the transition cycle and balance cycle refueling cycle can be achieved, the batch unloading burnup of the fuel assemblies can be significantly improved, higher fuel utilization can be achieved, and the core cycle length of the transition cycle and balance cycle can reach the 24-month long cycle refueling design requirement.

[0042] Furthermore, all circulating solid combustibles are integrated gadolinium solid combustibles in the form of gadolinium-loaded fuel rods, wherein the gadolinium-loaded fuel rods are formed by uniformly mixing UO2-Gd2O3 in fuel pellets;

[0043] The number of gadolinium-loaded fuel rods in the first cycle is 8, 12, 16 or 20;

[0044] The number of gadolinium-loaded fuel rods in each cycle from the second cycle to the balance cycle is 12, 16, 20 or 24.

[0045] Furthermore, in each cycle from the second cycle to the equilibrium cycle, the U-235 enrichment in the UO2-Gd2O3 fuel pellets is 2.5%, and the weight percentage of Gd2O3 is 10%.

[0046] By rationally designing the number of gadolinium-loaded fuel rods in the first cycle, transition cycle, and balance cycle, as well as the U-235 enrichment and weight percentage of Gd2O3 in the UO2-Gd2O3 fuel pellets in the transition cycle and balance cycle, the availability of the power plant after balancing reached 92%, achieving a higher availability of the power plant.

[0047] Furthermore, the new fuel assemblies for the first cycle are loaded in four zones according to the enrichment of U-235. The enrichment of U-235 in the four zones are 3.1%, 3.9%, 4.45% and 4.95% respectively. The new fuel assemblies with enrichment of U-235 of 3.1%, 3.9%, 4.45% and 4.95% are 69, 36, 36 and 36 groups respectively. The new fuel assemblies for the first cycle are arranged in a high leakage loading mode.

[0048] Furthermore, the high leakage loading mode is as follows: the new fuel assembly with the highest enrichment is placed at the outermost circle of the core, and the new fuel assemblies with other enrichments are combined with each other according to the enrichment levels.

[0049] Among them, the enrichment degrees of the other new fuel assemblies are different. The new fuel assemblies with slightly higher enrichment degrees and the new fuel assemblies with lower enrichment degrees are combined with each other inside the core.

[0050] Furthermore, in the first cycle, the enrichment of U-235 in the UO2-Gd2O3 fuel pellets in the new fuel assemblies with enrichments of U-235 of 3.1%, 3.9%, 4.45% and 4.95% were 1.8%, 2.2%, 2.5% and 2.5%, respectively, and the weight percentage of Gd2O3 in the UO2-Gd2O3 fuel pellets was 8%.

[0051] By rationally designing new fuel assemblies with different enrichment levels in the first cycle, adopting a high leakage loading mode, and rationally designing the number of new fuel assemblies, a fuel replacement strategy for the first cycle of 24 months is achieved.

[0052] An embodiment of the present invention provides a fuel loading method for a pressurized water reactor core with a 24-month refueling cycle, which uses two new fuel assemblies with a fuel enrichment of more than 5% for refueling; the cycle lengths of the first cycle, transition cycle and balancing cycle all reach 24 months, and the power plant availability after balancing reaches 92%; the refueling cycle adopts an extremely low leakage loading method and rationally utilizes reusable assemblies, and the batch unloading fuel consumption of the fuel assemblies is significantly improved.

[0053] This method takes into account both increasing the cycle length and flattening the core power distribution, greatly improving the utilization rate of nuclear fuel and the availability of power plants, bringing a series of benefits such as increasing power generation, reducing the number of overhauls, reducing the generation of high-level radioactive waste, and reducing the level of radioactive exposure of power plant workers. Since the solid combustible poisons and fuel materials used are very mature and technically easy to implement, it can be applied to new power plants using 177 cores and is extremely economical.

[0054] Example 1

[0055] This embodiment is aimed at a reactor core of a million-kilowatt nuclear power plant, which is composed of 177 AFA3G fuel assemblies. This embodiment realizes 24-month refueling from the first cycle, and provides a fuel loading scheme for quickly achieving a 24-month refueling balance cycle.

[0056] like Figure 1As shown, the first cycle core loading uses four fuel assemblies with different U-235 enrichments, 69, 36, 36 and 36 sets of fuel assemblies with 3.1%, 3.9%, 4.45% and 4.95% enrichments respectively. Considering that all the fuel assemblies used in the first cycle are new fuel assemblies, in order to effectively flatten the core power distribution, a high leakage loading mode is adopted. The new fuel assemblies with the highest enrichment of 4.95% are arranged at the outermost circle of the core, and the other three new fuel assemblies with enrichments of 3.1%, 3.9% and 4.45% are arranged inside the core, and the three new fuel assemblies with lower enrichments are arranged in a cross checkerboard pattern inside the core. The first cycle solid burnable poison is gadolinium, the enrichment of U-235 is 3.1%, 3.9%, 4.45% and 4.95%, the U-235 enrichment in the UO2-Gd2O3 fuel pellets is 1.8%, 2.2%, 2.5% and 2.5% respectively, and the weight percentage of Gd2O3 is 8%. The typical number of gadolinium-loaded fuel rods in the new fuel assembly is 8, 12, 16 or 20.

[0057] The above-mentioned first cycle core loading method can meet the safety criteria requirements, and its main calculation results are shown in Table 1.

[0058] Table 1 Calculation results of the first cycle core loading method

[0059]

[0060] From the second cycle to the balance cycle, the enrichment of the new fuel assemblies used for refueling is 5.45% and 5.95%. The fuel assemblies of the transition cycle and the balance cycle are arranged in a low leakage mode. The 80 new fuel assemblies added each time in each cycle from the second cycle to the balance cycle are placed inside the core, and the old fuel assemblies with deeper burnup that have been burned through multiple cycles are placed in the outermost circle of the core. There are also multiple old fuel assemblies that have been burned through in the inner circle of the core, and the old fuel assemblies in the inner circle of the core are combined with the new fuel assemblies. The old fuel assemblies in the inner circle can also be arranged in a cross-arrangement according to the different burnup depths of the assemblies. For specific core loading methods for the second cycle, the third cycle, and the balance cycle, see Figure 2-4 .

[0061] The solid burnable poison of the transition cycle and the balance cycle fuel assembly also uses gadolinium, and the U-235 enrichment in the UO2-Gd2O3 fuel pellets is 2.5% and the weight percentage of Gd2O3 is 10%. The typical number of gadolinium-loaded fuel rods in each new fuel assembly from the second cycle to the balance cycle is 12, 16, 20 or 24.

[0062] The main calculation results of the core of the transition cycle and the balance cycle are shown in Table 2. It can be seen from Table 2 that the core loading method described in this embodiment can quickly realize the 24-month long-cycle refueling design; the cycle length of the balance cycle is 665 equivalent full power days; the power plant availability rate reaches 92%; at the same time, it takes into account the flattening of the core power distribution and the increase of the cycle length of the subsequent cycle core, thereby improving the utilization rate of nuclear fuel and the operating economy of the power plant. The maximum nuclear enthalpy rise factor meets the safety limit requirement of not exceeding 1.65, and the average fuel consumption of the maximum unloading assembly is less than 62GWd / tU.

[0063] Table 2 Transition cycle and balance cycle core calculation results

[0064]

[0065] The embodiment of the present invention provides a method for loading fuel for a pressurized water reactor core with a 24-month refueling cycle. The core of a million-kilowatt pressurized water reactor is composed of 177 fuel assemblies, and the technical requirements for a 24-month long-cycle refueling design starting from the first cycle are met. After balancing, the power plant availability reaches 92%. After balancing, the average batch unloading fuel consumption of each batch of fuel assemblies reaches 58,000 MWd / tU, which is about 10,000 MWd / tU higher than the highest batch unloading fuel consumption of the 18-month fuel design of the same type of reactor.

[0066] The methods, processes, devices, etc. not involved in the present invention are all known technologies and will not be described in detail here.

[0067] The above specific implementation methods further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for loading fuel for a pressurized water reactor core during a 24-month refueling cycle, characterized in that: The core of the pressurized water reactor is composed of 177 fuel assemblies. The first cycle of the core adopts a 24-month refueling strategy. Each refueling of the core from the second cycle to the balance cycle adopts new fuel assemblies with U-235 enrichment of (5%~5.95%); After balancing, the average batch unloading burnup of each batch of fuel assemblies reached 58,000 MWd / tU; The core is loaded with 80 new fuel assemblies each time from the second cycle to the balance cycle; The new fuel assemblies for the first cycle are loaded in four zones according to the U-235 enrichment. The U-235 enrichment of the new fuel assemblies in the four zones are 3.1%, 3.9%, 4.45% and 4.95% respectively. There are 69, 36, 36 and 36 groups of new fuel assemblies with U-235 enrichment of 3.1%, 3.9%, 4.45% and 4.95% respectively. The new fuel assemblies for the first cycle are arranged in a high leakage loading mode.

2. A method for loading fuel for a pressurized water reactor core during a 24-month refueling cycle according to claim 1, characterized in that: The enrichment levels of the two new fuel assemblies exceeding 5% U-235 enrichment are 5.45% and 5.95% respectively.

3. The method for loading fuel for a pressurized water reactor core during a 24-month refueling cycle according to claim 1, characterized in that: The fuel assemblies of each cycle from the second cycle to the balance cycle are arranged in a low leakage mode, with the old fuel assemblies that have been burned deeply placed in the outermost circle of the core, and the new fuel assemblies and the old fuel assemblies that have been burned placed in the inner circle of the core and arranged in a cross-spaced manner.

4. A method for loading fuel for a pressurized water reactor core during a 24-month refueling cycle according to claim 3, characterized in that: The burned-up old fuel assemblies placed in the inner ring of the core are arranged in a cross pattern according to the burn-up depth.

5. The method for loading fuel for a pressurized water reactor core during a 24-month refueling cycle according to claim 1, characterized in that: All circulating solid combustibles are integrated gadolinium solid combustibles in the form of gadolinium-loaded fuel rods, wherein the gadolinium-loaded fuel rods are formed by uniformly mixing UO2-Gd2O3 in fuel pellets; The number of gadolinium-loaded fuel rods in the first cycle is 8, 12, 16 or 20; The number of gadolinium-loaded fuel rods in each cycle from the second cycle to the balance cycle is 12, 16, 20 or 24.

6. A method for loading fuel for a pressurized water reactor core during a 24-month refueling cycle according to claim 5, characterized in that: The U-235 enrichment in the UO2-Gd2O3 fuel pellets in each cycle from the second cycle to the equilibrium cycle is 2.5%, and the weight percentage of Gd2O3 is 10%.

7. The method for loading fuel for a pressurized water reactor core during a 24-month refueling cycle according to claim 1, characterized in that: The high leakage loading mode is as follows: the new fuel assembly with the highest enrichment is placed at the outermost circle of the core, and the new fuel assemblies with other enrichments are combined with each other according to the enrichment levels.

8. The method for loading fuel for a pressurized water reactor core during a 24-month refueling cycle according to claim 1, characterized in that: In the first cycle, the enrichments of U-235 in the UO2-Gd2O3 fuel pellets in the new fuel assemblies with U-235 enrichments of 3.1%, 3.9%, 4.45% and 4.95% were 1.8%, 2.2%, 2.5% and 2.5% respectively, and the weight percentage of Gd2O3 in the UO2-Gd2O3 fuel pellets was 8%.

Images