Fuel element

Abstract

The invention discloses a fuel element, and relates to the technical field of nuclear engineering. The element comprises a plurality of fuel pellets and a plurality of fuel cores, and the rib net is composed of ribs, and the rib net is connected with the fuel core block. The rib net is arranged to divide the internal space of the element into a plurality of communicated lattice cells, part of the lattice cells are filled with the fuel pellets, and part of the lattice cells are reserved to serve as gas collecting cavities, so that gas generated in the fission process can be effectively released and migrated into the cavities, pressure accumulation and volume expansion in fuel are reduced, and the fuel efficiency is improved. The extrusion effect of the fuel on the cladding is obviously reduced; meanwhile, due to the structure of the rib net, the overall strength and stability of the element are enhanced, the capacity of bearing internal loads is improved, and the risk that the cladding bulges or is damaged is avoided; and the gap design between the fuel core block and the rib further accommodates the expansion deformation of the fuel, so that the service life of the element is finally prolonged, and the economical efficiency and the operation allowance of the reactor are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear engineering, and in particular to a fuel element. BACKGROUND

[0002] The fuel element in a nuclear energy reactor is the core component that generates nuclear fission reactions and releases energy. The plate-shaped metal fuel element is composed of a metal fuel core and a sealed cladding wrapped outside. Its flat structure and large heat transfer area are conducive to efficient heat dissipation and lower fuel operating temperature, so it is widely used in research reactors and some advanced reactor designs. The manufacturing process of such elements is relatively simple, suitable for mass production, and has good economy and safety.

[0003] However, metal fuel will produce fission gas in the irradiation environment, causing the fuel volume to expand and squeeze the cladding, especially under high temperature and high power conditions. The existing plate-shaped fuel element is limited by its flat structure and weak mechanical constraints, and it is difficult to effectively accommodate the pressure caused by gas release, and is usually only suitable for low temperature working conditions. Although some designs have tried to accommodate gas by constructing internal cavities or partition grids, they often need to sacrifice too much fuel loading space, resulting in a decrease in neutron economy, which cannot meet the requirements of high power density and neutron flux for the new generation of high-flux research test reactors. Therefore, the existing plate-shaped metal fuel element scheme is difficult to adapt to such high temperature and high burnup service environment. SUMMARY

[0004] Therefore, the present application provides a fuel element, which mainly aims to solve the technical problem that the existing plate-shaped metal fuel element scheme is difficult to adapt to such high temperature and high burnup service environment.

[0005] The present application provides a fuel element, comprising: a plurality of fuel pellets; a rib web composed of ribs, the rib web being connected to the fuel pellets.

[0006] In a feasible implementation, the element further comprises: a cladding connected to the rib web, the fuel pellets and the rib web being arranged inside the cladding.

[0007] In a feasible implementation, the element further comprises: a frame connected to the cladding, the fuel pellets and the rib web being arranged inside the frame.

[0008] In a feasible implementation, the element further comprises: A grid element, wherein there are multiple grid elements, is formed by the ribs dividing the internal space enclosed by the shell and the frame.

[0009] In one feasible implementation, the element further includes: A through hole is formed on the rib to connect multiple gate elements.

[0010] In one feasible implementation, the gate element includes: The first grid cell, which is a partial grid cell, contains the fuel pellet.

[0011] In one feasible implementation, the gate element further includes: The second gate element is a remaining gate element, and the second gate element contains a cavity.

[0012] In one feasible implementation, the element further includes: A barrier layer is disposed between the fuel pellet and the casing.

[0013] In one feasible implementation, a gap is provided between the fuel pellet and the rib mesh.

[0014] In one feasible implementation, the fuel pellets are made of metallic fuel.

[0015] This application provides a fuel element, comprising: a fuel pellet, wherein the number of fuel pellets is plurality of; and a rib mesh, wherein the rib mesh is composed of ribs and is connected to the fuel pellet.

[0016] This application divides the internal space of the reactor element into multiple interconnected cells by setting a rib mesh. Some cells are filled with fuel pellets, while others are left empty as gas collection chambers. This allows the gas generated during fission to be effectively released and migrated into the cavities, thereby reducing the pressure accumulation and volume expansion inside the fuel and significantly reducing the compression effect of the fuel on the cladding. At the same time, the structure of the rib mesh enhances the overall strength and stability of the reactor element, improves its ability to bear internal loads, and avoids the risk of cladding bulging or breakage. The gap design between the fuel pellets and the ribs further accommodates the expansion and deformation of the fuel, while the good combination of fuel and cladding ensures efficient heat dissipation, reduces the operating temperature, and improves the safety and reliability of the reactor element under high temperature and high power conditions. Ultimately, this extends the life of the reactor element and improves the economy and operating margin of the reactor.

[0017] Other features and advantages of this application will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings.

[0018] The technical solution of this application will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 A schematic diagram of the structure of a fuel element provided in an embodiment of this application is shown; Figure 2 A schematic diagram of another fuel element provided in an embodiment of this application is shown.

[0020] In the picture: 1. Fuel pellet; 2. Rib mesh; 3. Sheath; 4. Frame. Detailed Implementation

[0021] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0023] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0024] Plate-shaped metallic fuel elements consist of a metallic fuel core and a cladding surrounding the core, with the core and cladding metallurgically bonded together. Plate-shaped metallic fuel elements possess significant advantages such as high thermal conductivity, large heat transfer area, small thermal energy storage, and large safety margin, which are beneficial for increasing core specific power and reducing fuel center temperature, thereby improving fuel utilization. The manufacturing process of plate-shaped fuel elements is simple, easy to scale up, and has certain economic advantages. Therefore, they have wide applications in the field of research and experimental reactor fuels and can also serve as candidate fuel schemes for fourth-generation advanced nuclear energy systems and next-generation high-flux research reactors.

[0025] Metallic fuels exhibit significant volume swelling under neutron irradiation. As fission products accumulate, the fuel phase volume continuously increases, directly causing mechanical interactions between the fuel and its cladding. This can lead to cladding damage and loss of component integrity. The swelling behavior of metallic fuels has become one of the important limitations restricting the safe service of this type of fuel. Metallic fuel swelling is mainly caused by solid and gaseous fission products retained in the fuel, with insoluble gaseous fission products being the main contributor to irradiation swelling (i.e., gas swelling).

[0026] To alleviate the swelling and deformation of metallic fuel, the following two aspects are mainly addressed: 1) Enhancing external constraints, mainly through methods such as selecting stronger cladding materials and increasing the pressure of the coolant system outside the cladding. However, these methods only have a certain inhibitory effect on gas swelling during the bubble growth stage under medium and low temperature conditions, and have no effect on solid swelling or gas swelling caused by equilibrium bubbles at higher temperatures; 2) Reducing internal loads by reserving space for fuel swelling and gas release, thereby reducing fuel-cladding interaction by containing fuel swelling volume deformation. The feasibility of this method has been verified in the design of rod-shaped metallic fuel elements. EBR-II and FFTF irradiation experience shows that rod-shaped metallic fuel elements with low effective density and atmospheric cavity structure can achieve 18.4% FIMA burnup without damage.

[0027] Due to their inherent structural characteristics (high aspect ratio), small thickness dimensions, weak mechanical constraints, and very low stiffness, plate-shaped fuel elements preferentially deform along their thickness direction, and the difference in deformation along this direction is essentially unadjustable. Therefore, plate-shaped fuel elements are generally considered suitable only for cryogenic environments, i.e., temperature ranges where fission gas products are not released in large quantities from the fuel, thus containing the fission products and ensuring that the element's thickness deformation is within acceptable limits. For example, the widely used U-Mo / Al monolithic fuel element is mainly designed for water-cooled research reactor operation. Its power level and fuel temperature are relatively low (not exceeding 250°C), the fission product diffusion and migration rates and fission gas swelling are small, and the mechanical load of the core on the cladding is not strong, which can basically meet the structural integrity requirements of the element throughout its target service life.

[0028] At higher power levels or operating temperatures, the swelling of metallic fuel and the release of fission gases will be significantly enhanced. The accumulation and interconnection of fission gases within the core will, on the one hand, reduce the core's thermal conductivity, affecting heat removal from the fuel; on the other hand, it will directly cause intensified core swelling, leading to increased mechanical interaction between the fuel and cladding, directly threatening the integrity of the cladding structure and the safety of the fuel elements. Existing data shows that at temperatures approaching or exceeding 400°C, even with rod-shaped element structures, the swelling and compression of metallic fuel will cause rapid cladding failure. The highest burnup of rod-shaped metallic fuel elements in first-generation fast reactors does not exceed 3% FIMA. For plate-shaped fuel elements, their cladding structure's ability to withstand internal pressure loads is far less than that of rod-shaped fuel elements, and they are expected to fail more quickly.

[0029] Reference CN101243521B proposes a large-structure composite plate-type fuel element for a gas-cooled fast reactor (GFR). This element divides the internal space of the plate into multiple independent small cells, each containing a fuel pellet. The sealed small cells serve to contain fission products. While this structure provides space for containing gaseous fission products (i.e., fuel-free areas within the small cells) and allows for the release of fission gases, the gas cavity shares cell space with the fuel. To ensure the structural safety of the cell at high temperatures, a high gas-fuel volume ratio (close to or exceeding 1) is required, thus reducing the pressure within the cell. This directly leads to a decrease in fuel load, poor neutron economy, and is detrimental to improving neutron flux and power levels. High-flux research reactors have high requirements for neutron flux and power levels; therefore, existing plate-type metallic fuel element designs are not suitable for the operational conditions of next-generation high-flux research reactors.

[0030] See Figure 1 The diagram illustrates a structural schematic of a fuel element according to an embodiment of this application, comprising: Fuel pellet 1, and there are multiple fuel pellets 1; Rib mesh 2, which is composed of ribs, is connected to fuel pellet 1.

[0031] In the above embodiment, the rib mesh 2 is a grid structure composed of multiple interconnected ribs, forming regular grid spaces between the ribs. The fuel pellet 1 is placed within these grid spaces, maintaining a non-contact state with the inner wall of the ribs, and the connection is achieved through the structural positioning of the grid. The overall structure of the rib mesh 2 is fixedly connected to the upper and lower cladding layers by welding or metallurgical bonding to form a stable support frame.

[0032] This connection method allows the rib mesh 2 to provide a stable housing space for the fuel pellet 1 while maintaining the relative independence of the fuel pellet 1. The grid design of the rib mesh 2 enhances the overall structural strength of the component, effectively dispersing mechanical stress and preventing local deformation. The connectivity between the grids ensures the smooth migration of fission gas, providing a channel for the gas from the fuel region to the collection chamber, thereby reducing internal pressure accumulation and mitigating the impact of fuel swelling on the cladding 3.

[0033] Furthermore, the components also include: The casing 3 is connected to the rib mesh 2, and the fuel pellet 1 and the rib mesh 2 are located inside the casing 3.

[0034] In the above embodiments, the cladding 3 and the rib mesh 2 are connected by welding or metallurgical bonding to form a sealed outer covering layer that completely encloses the fuel pellet 1 and the rib mesh 2. The cladding 3 has a flat plate structure, covering the upper and lower surfaces of the rib mesh 2 and tightly engaging with the edges of the rib mesh 2 to ensure that the internal components are firmly fixed and sealed.

[0035] The enclosure 3 provides an external protective barrier to prevent coolant from entering or internal substances from leaking. At the same time, in combination with the rib mesh 2, it enhances the overall mechanical strength of the component, enabling the component to better withstand internal pressure changes and external mechanical loads, thereby improving the component's durability and safety.

[0036] Furthermore, the components also include: Frame 4 is connected to shell 3, and fuel pellet 1 and rib mesh 2 are located inside frame 4.

[0037] In the above embodiments, the frame 4 and the shell 3 are connected by peripheral welding or integral molding, forming a frame structure around the shell 3, completely enclosing the fuel pellet 1 and the rib mesh 2 inside the frame 4. The frame 4 adopts a rectangular or ring-shaped design, and together with the shell 3, it forms a complete housing space.

[0038] The frame 4 increases the structural stability and edge strength of the component, helps to disperse stress and prevent deformation, especially in high temperature and irradiation environments, the frame 4 can maintain the shape of the component and reduce the risk of edge breakage due to swelling or pressure.

[0039] Furthermore, the components also include: A grid cell, which consists of multiple grid cells, is formed by dividing the internal space of the shell 3 and the border 4 by ribs.

[0040] In the above embodiments, the grid element is formed by dividing the internal space enclosed by the shell 3 and the frame 4 by ribs. There are multiple grid elements, and each grid element is separated by the rib wall to form an independent unit. The shape of the grid element is preferably a regular polygon, such as a honeycomb or rectangle, to optimize space utilization and structural uniformity.

[0041] The partitioned structure of the cells allows for modularization of the fuel and gas containment areas, improving the organization and manageability of the components, facilitating the zonal collection of fission gases and localized control of fuel, thereby enhancing the overall performance and reliability of the components.

[0042] Furthermore, the components also include: Through holes are formed on ribs and are used to connect multiple gate cells.

[0043] In the above embodiments, through holes are formed on the ribs. These through holes are small openings or slits, evenly distributed in the rib wall, connecting adjacent grid cells and allowing the internal spaces of each grid cell to communicate with each other. The size and distribution of the through holes ensure that gas can flow freely while maintaining the structural integrity of the ribs.

[0044] The through-hole design allows fission gas to migrate from the fuel region to the cavity region, effectively reducing pressure accumulation inside the fuel, minimizing the effects of gas swelling, promoting uniform gas distribution, and avoiding failures caused by local high-pressure points.

[0045] Furthermore, the gate element includes: The first cell, which is a partial cell, contains a fuel pellet 1.

[0046] In the above embodiments, the first grid cell is a part of a grid cell, and a fuel pellet 1 is disposed within the first grid cell. The fuel pellet 1 is placed at the center of the grid cell or at an appropriate position, maintaining a certain distance from the grid cell wall. The first grid cells together constitute the active region of the element, which is used for nuclear fission reactions.

[0047] The first cell is centrally loaded with fuel, which optimizes neutron economy and power density, making the fission reaction more efficient. At the same time, due to the cell separation, the influence of local hot spots is limited, improving the thermal management capability and operational stability of the element.

[0048] Furthermore, the gate element also includes: The second cell is the remaining cell, and the second cell contains a cavity.

[0049] In the above embodiments, the second cell is the remaining portion of the cell, and the second cell is a cavity that is not filled with any fuel. The volume of the cavity is designed according to the gas capacity requirements. The second cell is typically located at one or both ends of the element to maximize neutron utilization efficiency.

[0050] The second cell, serving as a fission gas collection chamber, provides a dedicated space to contain the released gas, thereby significantly reducing the expansion pressure in the fuel region, mitigating the mechanical interaction between the fuel and the cladding 3, extending the element's lifespan, and increasing the safety margin.

[0051] Furthermore, the components also include: A barrier layer is provided between the fuel pellet 1 and the casing 3.

[0052] In the above embodiments, a barrier layer is disposed between the fuel pellet 1 and the casing 3. The barrier layer is a thin-layer material, applied by coating or interlayering, and is well bonded to the surfaces of the fuel pellet 1 and the casing 3. The barrier layer material is selected to be of the type that can inhibit element diffusion, such as an anti-FCCI barrier layer or a metal composite layer.

[0053] The barrier layer effectively prevents chemical interactions or interdiffusion of elements between the fuel and the cladding 3, reduces the risk of chemical interactions between the fuel and the cladding, thereby maintaining the integrity of the cladding 3, reducing the probability of failure, and improving the durability of the component in high-temperature environments.

[0054] Furthermore, a gap is provided between the fuel pellet 1 and the rib mesh 2.

[0055] In the above embodiment, a gap is provided between the fuel pellet 1 and the rib mesh 2. The gap is a small space surrounding the side of the fuel pellet 1, allowing the fuel pellet 1 a certain amount of movement space within the grid. The size of the gap is designed according to the fuel swelling characteristics to ensure that heat conduction is not affected.

[0056] The gap accommodates the volume expansion of the fuel pellet 1 under irradiation, reduces the stress caused by direct mechanical contact, alleviates the compression between the fuel and the ribs, thereby reducing the risk of deformation and maintaining the structural consistency of the component.

[0057] Furthermore, the fuel pellet 1 is made of metallic fuel.

[0058] In the above embodiments, the fuel pellet 1 is made of metallic fuel, including uranium-zirconium alloy, uranium-molybdenum alloy, multi-element uranium alloy, etc., or metal compounds containing hydrogen moderators such as zirconium hydride and yttrium hydride. The fuel pellet 1 is formed into a block or sheet shape through a molding process, and has high density and good thermal conductivity.

[0059] Metallic fuel materials offer excellent thermal conductivity, which facilitates the rapid removal of fission heat and reduces the fuel core temperature. At the same time, the compatibility of metallic fuels makes them suitable for various reactor types, enhancing the applicability and economy of the components.

[0060] Example 1: See Figure 1 This illustration shows a compartmentalized honeycomb grid plate-type fuel element provided in an embodiment of this application. Its structure includes: a pellet, a rib mesh, a frame, and a cladding. The rib mesh divides the internal space of the element into several honeycomb-shaped grids, with intermittent or transverse openings in the ribs allowing interconnection between the grid spaces. Circular pellets are inserted into some of the grids, with gaps between the pellets and the ribs forming the grids. The grids without pellets collectively form a fissile gas containment chamber, which can be located at one end of the element or distributed at both ends. The frame and cladding seal the rib mesh and pellets inside the element, ensuring a good fit between the rib mesh and pellets and the upper and lower cladding, and preventing large-area detachment during service.

[0061] The cladding and frame are made of the same material, but zirconium alloy, stainless steel, aluminum alloy, or other materials can be selected based on the core energy spectrum range and functional requirements. The rib mesh can be made of the same material as the cladding, or it can be made of a different material as needed. Various methods should be used to ensure a good bond between the rib mesh and the cladding.

[0062] The pellet material can be determined based on the core energy spectrum range and functional requirements. It is recommended to select uranium alloy fuels such as U-Zr, U-Mo, U-Pu-Zr, and U-Pu-Mo. Various means should be used to ensure good bonding between the pellets and the cladding.

[0063] Example 2: See Figure 2 This illustration shows a compartmentalized rectangular grid plate fuel element provided in an embodiment of this application. Its structure includes: a pellet, a rib mesh, a frame, and a casing. The rib mesh divides the internal space of the element into several rectangular grids, with intermittent ribs or transverse openings allowing interconnection between the grid spaces. Rectangular or other shaped pellets are inserted into some of the grids, with gaps between the pellets and the ribs forming the grids. The grids without pellets collectively form a fissile gas containment chamber, which may be located at one end of the element or distributed at both ends. The frame and casing seal the rib mesh and pellets inside the element, ensuring a good fit between the rib mesh and pellets and the upper and lower casings, and preventing large-area detachment during service.

[0064] The material selection for the plate-type fuel element in this embodiment is the same as that in Embodiment 1.

[0065] This application provides a schematic diagram of a fuel element structure, including: multiple fuel pellets; and a rib mesh composed of ribs connected to the fuel pellets. This application divides the internal space of the element into multiple interconnected cells by setting the rib mesh. Some cells are filled with fuel pellets, while others are left empty as gas collection chambers. This allows the gas generated during fission to be effectively released and migrated into the cavities, thereby reducing internal pressure accumulation and volume expansion of the fuel, significantly reducing the pressure exerted by the fuel on the cladding. Simultaneously, the rib mesh structure enhances the overall strength and stability of the element, improves its ability to bear internal loads, and avoids the risk of cladding bulging or breakage. The gap design between the fuel pellets and the ribs further accommodates fuel expansion and deformation, while the good integration of the fuel and cladding ensures efficient heat dissipation, reduces operating temperature, and improves the safety and reliability of the element under high-temperature and high-power conditions, ultimately extending the element's lifespan and improving the reactor's economy and operating margin.

[0066] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of a preferred embodiment, and the modules or processes shown in the drawings are not necessarily essential for implementing this application. Those skilled in the art will understand that the modules in the apparatus of the embodiment can be distributed within the apparatus of the embodiment as described, or can be modified to be located in one or more apparatuses different from this embodiment. The modules of the above-described embodiment can be combined into one module, or further divided into multiple sub-modules.

[0067] The serial numbers in this application are for descriptive purposes only and do not represent the superiority or inferiority of any particular implementation scenario. The above disclosures are merely a few specific implementation scenarios of this application; however, this application is not limited thereto, and any variations conceived by those skilled in the art should fall within the protection scope of this application.

Claims

1. A fuel element, characterized in that, include: Fuel pellets (1), wherein the number of fuel pellets (1) is multiple; Rib mesh (2), which is composed of ribs, is connected to the fuel pellet (1).

2. The element according to claim 1, characterized in that, The element also includes: The shell (3) is connected to the rib mesh (2), and the fuel pellet (1) and the rib mesh (2) are located inside the shell (3).

3. The element according to claim 2, characterized in that, The element also includes: The frame (4) is connected to the shell (3), and the fuel pellet (1) and the rib mesh (2) are located inside the frame (4).

4. The element according to claim 3, characterized in that, The element also includes: A grid element, the number of which is multiple, is formed by the ribs dividing the internal space enclosed by the shell (3) and the frame (4).

5. The element according to claim 4, characterized in that, The element also includes: A through hole is formed on the rib to connect multiple gate elements.

6. The element according to claim 4, characterized in that, The gate element includes: The first cell is a partial cell, and the fuel pellet (1) is disposed within the first cell.

7. The element according to claim 6, characterized in that, The gate element also includes: The second gate element is a remaining gate element, and the second gate element contains a cavity.

8. The element according to claim 2, characterized in that, The element also includes: A barrier layer is provided between the fuel pellet (1) and the casing (3).

9. The element according to claim 1, characterized in that, A gap is provided between the fuel pellet (1) and the rib mesh (2).

10. The element according to claim 1, characterized in that, The fuel pellet (1) is made of metallic fuel.

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