SiC cladding fuel element

Abstract

The utility model discloses a SiC cladding fuel element. The SiC cladding fuel element comprises a SiC cladding, at least one metal foil and at least one fuel pellet, at least one fuel pellet is packaged in the metal foil to form a packaged pellet unit; and the packaging core block unit is arranged in the SiC cladding. According to the SiC cladding fuel element, the fuel pellet is packaged in the metal foil, and the metal foil can contain fission gas, so that the airtightness maintaining capability of the SiC cladding is improved, and the risk that the fission gas of the SiC cladding fuel element leaks is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of nuclear fuel, in particular to a SiC cladding fuel element. Background Art

[0002] In water-cooled reactors such as pressurized water reactors (PWRs), pressurized heavy water reactors (PHWRs), and boiling water reactors (BWRs), the reactor core consists of numerous fuel assemblies. Each fuel assembly contains multiple fuel elements, each composed of fuel pellets (such as UO2 or MOX (UO2-PuO2)) sealed in zirconium alloy cladding tubes. The zirconium alloy cladding tubes react with high-temperature water, releasing both heat and flammable gases. Improper handling could result in a large-scale radioactive leak or a serious accident, such as a core melt.

[0003] A new fuel element design improvement involves replacing zirconium alloy cladding with a SiC fiber-reinforced SiC matrix composite cladding (hereafter referred to as SiC cladding). The reduced thermal conductivity of SiC cladding under irradiation can lead to large thermal gradients across the cladding wall thickness, particularly under high heat flux conditions. These differential irradiation swelling along the thermal gradient can cause cladding cracking, leading to loss of hermeticity. Therefore, improving the ability of SiC-clad fuel elements to maintain hermeticity has received significant attention. Utility Model Content

[0004] The technical problem to be solved by the utility model is to provide a SiC cladding fuel element with improved airtightness maintenance capability.

[0005] The technical solution adopted by the utility model to solve the technical problem is: to provide a SiC cladding fuel element, including a SiC cladding, at least one metal foil and at least one fuel pellet;

[0006] At least one fuel pellet is encapsulated in the metal foil to form an encapsulated pellet unit; and the encapsulated pellet unit is disposed in the SiC cladding.

[0007] In some embodiments, the metal foil has a thickness of 10 micrometers to 200 micrometers.

[0008] In some embodiments, the metal foil is one or more of gold foil, silver foil, copper foil, aluminum foil, magnesium foil, nickel foil, tantalum foil, tungsten foil, zirconium foil, titanium foil, niobium foil, molybdenum foil, indium foil, gadolinium foil, and stainless steel foil.

[0009] In some embodiments, the fuel pellets are solid pellets or mesoporous pellets.

[0010] In some embodiments, the gap width between the metal foil and the fuel pellet is 0.05 mm to 0.20 mm.

[0011] In some embodiments, the gap width between the SiC cladding and the metal foil is 0.05 mm to 0.20 mm.

[0012] In some embodiments, the number of fuel pellets encapsulated in the metal foil is 1 to 3.

[0013] In some embodiments, the SiC clad fuel element further includes a heat-conducting gas or a low-melting-point metal filling a gap between the metal foil and the fuel pellet, and / or a gap between the SiC cladding and the metal foil.

[0014] In some embodiments, the metal foil includes a sidewall surrounding the outer periphery of the fuel pellet and an end portion surrounding the end surface of the fuel pellet; the sidewall is folded to form a multi-bend structure.

[0015] In some embodiments, the end portion is in contact with an end surface of the fuel pellet.

[0016] The beneficial effects of the present invention are as follows: by encapsulating the fuel pellets in the metal foil, the metal foil can contain the fission gas, thereby improving the airtightness maintenance capability of the SiC cladding and reducing the risk of fission gas leakage in the SiC cladding fuel element. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0018] Figure 1 This is a schematic diagram of the radial cross-sectional structure of the SiC cladding fuel element of the present invention;

[0019] Figure 2 This is a schematic diagram of the axial cross-sectional structure of the SiC clad fuel element according to the first embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of the axial cross-sectional structure of a SiC clad fuel element according to the second embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram of the axial cross-sectional structure of a SiC clad fuel element according to the third embodiment of the present invention;

[0022] Figure 5 This is a schematic structural diagram of an embodiment of the metal foil in the SiC cladding fuel element of the present invention;

[0023] Figure 6 It is a structural schematic diagram of another embodiment of the metal foil in the SiC cladding fuel element of the present invention. DETAILED DESCRIPTION

[0024] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific implementation methods of the present invention are now described in detail with reference to the accompanying drawings.

[0025] refer to Figure 1 The SiC-clad fuel element of the present invention may include a SiC cladding 10 and at least one encapsulated pellet unit 20 disposed within the SiC cladding 10. The encapsulated pellet unit 20 further includes a metal foil 21 and at least one fuel pellet 22, wherein the fuel pellet 22 is encapsulated within the metal foil 21.

[0026] When two or more encapsulated pellet units 20 are disposed within the SiC cladding 10, the encapsulated pellet units 20 are arranged along the axial direction of the SiC cladding 10. When two or more fuel pellets 22 are encapsulated within the metal foil 21, the fuel pellets 22 are stacked one above the other so that within the SiC cladding 10, the fuel pellets 22 are also arranged along the axial direction of the SiC cladding 10.

[0027] For example, in Figure 2 In the SiC clad fuel element of the first embodiment shown, a plurality of fuel pellets 22 are encapsulated in the metal foil 21 , and the plurality of fuel pellets 22 are arranged along the axial direction of the SiC cladding 10 .

[0028] exist Figure 3 In the SiC-clad fuel element of the second embodiment, at least two encapsulated pellet units 20 are disposed within the SiC cladding 10. Each encapsulated pellet unit 20 comprises a metal foil 21 and two fuel pellets 22 encapsulated therein. The two or more encapsulated pellet units 20 are arranged within the SiC cladding 10 along its axial direction.

[0029] exist Figure 4 In the SiC-clad fuel element of the third embodiment, at least two encapsulated pellet units 20 are disposed within the SiC cladding 10. Each encapsulated pellet unit 20 comprises a metal foil 21 and at least one fuel pellet 22 encapsulated therein. The number of fuel pellets 22 within an encapsulated pellet unit 20 can vary, and can include one, two, or more.

[0030] It can be understood that as the cladding of the fuel element, the two opposite ends of the SiC cladding 10 are sealed, for example, by SiC end plugs, etc., which will not be described in detail here.

[0031] Another example Figure 1As shown, the SiC cladding 10 comprises at least one layer of SiC matrix composite material reinforced with continuous SiC fibers. Within the SiC cladding 10, a gap A exists between the encapsulated pellet units 20 and the inner wall of the SiC cladding 10 (i.e., between the metal foil 21 and the SiC cladding 10). This gap A has a width of 0.05 mm to 0.20 mm. This gap A provides space for thermal expansion and radiation swelling of the encapsulated pellet units 20.

[0032] If needed, to enhance the thermal conductivity of the SiC-clad fuel element, the gap A can serve as an air cavity filled with a heat-conducting gas; the heat-conducting gas is helium or a helium-xenon mixture. If needed, to enhance the radial thermal conductivity of the SiC-clad fuel element, the gap A can be filled with a low-melting-point metal selected from one or more of tin, sodium, potassium, indium, gallium, lead, bismuth, lithium, mercury, and zinc.

[0033] In the encapsulated pellet unit 20, the metal foil 21 serves as the outer layer encapsulating the fuel pellets 22. It can be one or more of gold foil, silver foil, copper foil, aluminum foil, magnesium foil, nickel foil, tantalum foil, tungsten foil, zirconium foil, titanium foil, niobium foil, molybdenum foil, indium foil, gadolinium foil, or stainless steel foil. The thickness of the metal foil ranges from 10 to 200 microns, preferably from 15 to 50 microns.

[0034] The number of fuel pellets 22 encapsulated in the metal foil 21 is 1 to 50. Considering the softness of the metal foil 21, the number of fuel pellets 22 encapsulated in the metal foil 21 is preferably 1 to 3.

[0035] By encapsulating the fuel pellets 22 with the metal foil 21 , the fission gas can be contained within the metal foil 21 , thereby reducing the risk of fission gas leakage.

[0036] A gap B is left within the metal foil 21 and between the metal foil 21 and the fuel pellets 22. The width of this gap B is 0.05 mm to 0.20 mm. This gap B provides space for thermal expansion and radiation swelling of the fuel pellets 22, as well as for the release of fission gases during normal operation.

[0037] If needed, to enhance the thermal conductivity of the SiC-clad fuel element, the gap B can be used as an air cavity filled with a heat-conducting gas; the heat-conducting gas is helium or a helium-xenon mixture. If needed, to enhance the radial thermal conductivity of the SiC-clad fuel element, the gap B can be filled with a low-melting-point metal selected from one or more of tin, sodium, potassium, indium, gallium, lead, bismuth, lithium, mercury, and zinc.

[0038] Fuel pellets 22 are made of a material containing uranium, plutonium, and / or thorium, and are selected from one or more of UO2, MOX (UO2-PuO2), UN, UC, U3Si2, ThO2, PuO2, PuN, PuC, and UB2. Fuel pellets 22 can be solid or mesoporous (having a central through hole). Mesoporous fuel pellets are preferred to provide more space for the fission gas and reduce the gas pressure within the metal foil 21.

[0039] Combine Figure 1 、 Figure 2 and Figure 5 、 Figure 6 The metal foil 21 may further include a sidewall 211 and an end portion 212. The sidewall 211 surrounds the outer periphery of the fuel pellet 22 and may be cylindrical; the end portion 212 surrounds the end surface of the fuel pellet 22. Therefore, the metal foil 21 has two end portions, corresponding to the two ends of the fuel pellet 22 or the ends of the two outermost fuel pellets 22.

[0040] To further enhance the radial heat conduction of the SiC-clad fuel element, the sidewall 211 of the metal foil 21 can be folded to form a multi-bend structure 213. The multi-bend structure 213 contacts the inner wall surface of the SiC cladding 10 and the surface of the fuel pellet 22 at opposite sides, forming a radial heat conduction path and improving the radial heat conduction effect.

[0041] The multi-bend structure 213 of the side wall 211 can be formed by connecting multiple V-shaped bends (e.g. Figure 5 As shown), or formed by connecting multiple U-shaped bends, or formed by connecting multiple trapezoidal polygons and other bends (as shown Figure 6 It can also be formed by combining two or more of the above-mentioned bending shapes.

[0042] In some embodiments, the end 212 of the metal foil 21 is in contact with the end surface of the fuel pellet 22. To this end, the end 212 of the metal foil 21 can also be configured in a dish shape that is in contact with the end surface of the fuel pellet 22, so that the end 212 and the end surface of the fuel pellet 22 are closely aligned and fit together, further enhancing the radial heat conduction of the SiC-clad fuel element.

[0043] In summary, in the SiC clad fuel element of the present invention, since the fuel pellets are encapsulated in the metal foil, the metal foil can contain the fission gas, thereby reducing the risk of fission gas leakage in the SiC clad fuel element.

[0044] In addition, the metal foil packaging structure of the fuel core, the filling of heat-conducting gas or low-melting-point metal in the gap, and the design of bent contacts enhance the radial thermal conductivity of the SiC cladding fuel element, reduce the temperature gradient of the SiC cladding in the service environment, thereby reducing the risk of SiC cladding cracking due to radiation swelling differences under thermal gradients, and further improving the SiC cladding's ability to maintain airtightness.

[0045] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the description and drawings of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A SiC clad fuel element, characterized in that: comprising a SiC cladding, at least one metal foil and at least one fuel pellet; At least one fuel pellet is encapsulated in the metal foil to form an encapsulated pellet unit; the encapsulated pellet unit is disposed in the SiC cladding; A gap is left inside the metal foil and between the metal foil and the fuel pellets, providing a containment space for the release of fission gas.

2. The SiC clad fuel element according to claim 1, characterized in that: The thickness of the metal foil is 10 microns to 200 microns.

3. The SiC clad fuel element according to claim 1, characterized in that: The metal foil is one or more of gold foil, silver foil, copper foil, aluminum foil, magnesium foil, nickel foil, tantalum foil, tungsten foil, zirconium foil, titanium foil, niobium foil, molybdenum foil, indium foil, gadolinium foil, and stainless steel foil.

4. The SiC clad fuel element according to claim 1, characterized in that: The fuel pellets are solid pellets or mesoporous pellets.

5. The SiC clad fuel element according to claim 1, characterized in that: The width of the gap between the metal foil and the fuel pellets is 0.05 mm to 0.20 mm.

6. The SiC clad fuel element according to claim 1, characterized in that: The width of the gap between the SiC shell and the metal foil is 0.05 mm to 0.20 mm.

7. The SiC clad fuel element according to claim 1, characterized in that: The number of the fuel pellets encapsulated in the metal foil is 1 to 3.

8. The SiC-clad fuel element according to any one of claims 1 to 7, characterized in that: The SiC cladding fuel element further includes a heat-conducting gas or a low-melting-point metal filling a gap between the metal foil and the fuel pellet, and / or a gap between the SiC cladding and the metal foil.

9. The SiC-clad fuel element according to any one of claims 1 to 7, characterized in that: The metal foil includes a side wall surrounding the outer periphery of the fuel pellet and an end portion surrounding the end surface of the fuel pellet; the side wall is folded to form a multi-bend structure.

10. The SiC clad fuel element according to claim 9, characterized in that: The end portion is in contact with the end surface of the fuel pellet.

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