Accident resistant fuel element

Abstract

The utility model discloses an accident-resistant fuel element. The accident-resistant fuel element comprises a cladding and at least one fuel capsule packaged in the cladding, the fuel capsule comprises a closed SiC composite material shell and at least one first fuel pellet loaded in the SiC composite material shell. According to the accident-resistant fuel element, the fuel core block is loaded through the SiC composite material to form the fuel capsule to be assembled in the cladding, the SiC composite material has excellent high-temperature-resistant strength and can contain rapid deformation of the fuel core block, and therefore the risks of cladding bulging, cracking and fuel repositioning under an LOCA accident are reduced, and after resubmerging quenching of the LOCA accident, the fuel capsule can be assembled in the cladding. Even if brittle fracture occurs in the cladding, the internal SiC composite material can still maintain re-submerging quenching to maintain integrity, so that the packaging of the fuel pellet is maintained.

Description

Technical Field

[0001] The utility model relates to the technical field of nuclear fuel elements, in particular to an accident tolerant 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 includes a large number of fuel assemblies, and each fuel assembly contains multiple fuel elements. The fuel element is formed by sealing fuel pellets (such as UO2, MOX (UO2-PuO2), etc.) in a zirconium alloy cladding tube.

[0003] After years of application of the zirconium alloy cladding, a mature and reliable supply guarantee system has been established, and it exhibits excellent service performance under normal operation. However, the ability of the zirconium alloy cladding fuel element to resist severe accidents needs to be further improved. In a hypothetical loss of coolant accident (LOCA), the zirconium alloy cladding will undergo a series of processes such as heating, bulging and rupturing, and high-temperature steam oxidation after rupture. After the LOCA accident occurs, the cladding temperature rises rapidly, triggering a chemical reaction between the zirconium alloy and water, releasing a large amount of heat and generating combustible gases. When the emergency core cooling water starts to inject water into the reactor core, a quench front will first form to cool the fuel rod cladding to 600°C - 800°C, and then a large amount of water will be injected for core cooling, causing the temperature of the cladding material to drop rapidly, resulting in quenching of the cladding. The rapid change process from high temperature to low temperature causes the cladding to be subjected to a strong thermal shock, and the zirconium alloy cladding may undergo brittle fracture under this strong thermal shock, causing the fuel pellets and their debris to accumulate and fall into the coolant. The cladding bulging in the LOCA accident will also cause the repositioning of the pellets, affecting the core coolability and the insertion of control rods. In a hypothetical reactivity insertion accident (RIA), the fuel pellets and their debris will also be scattered into the coolant through the rupture of the cladding.

[0004] To enhance the resistance of fuel elements to severe accidents, the nuclear energy industry has been exploring and developing accident-tolerant fuel elements with SiC composite claddings. Currently, the SiC composite claddings mainly include two design schemes: the all-ceramic composite design and the metal-ceramic hybrid design. However, the SiC composite cladding design scheme still faces challenges in aspects such as hydrothermal corrosion in the operating environment, sealed connection, airtightness maintenance, and long-size processing. For the design scheme of using a single SiC ceramic tube to wrap annular fuel pellets inside a zirconium alloy cladding, current tests have shown that the single SiC ceramic tube will fragment and break after high-temperature quenching or expansion plugging tests and cannot maintain its complete shape. After the zirconium alloy cladding is damaged, the fuel pellets wrapped by the single SiC ceramic tube may scatter in the reactor core. In addition, the above design requires a large amount of welding and sealing of single SiC ceramic tubes, increasing the processing burden and manufacturing cost. At the same time, compared with solid pellets, annular pellets reduce the fuel loading. Additionally, there is a large thermal resistance in the gap between the single SiC ceramic tube and the outer zirconium alloy cladding, affecting the radial heat transfer of the fuel element. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an accident-tolerant fuel element.

[0006] The technical solution adopted by the present invention to solve its technical problem is: to provide an accident-tolerant fuel element, including a cladding and at least one fuel capsule encapsulated in the cladding;

[0007] The fuel capsule includes a sealed SiC composite outer shell and at least one first fuel pellet loaded in the SiC composite outer shell.

[0008] In some embodiments, the SiC composite outer shell includes a SiC composite tube and at least one SiC end plug; the SiC end plug closes the end of the SiC composite tube.

[0009] In some embodiments, the first fuel pellet is a solid pellet.

[0010] In some embodiments, the wall thickness of the cladding is 0.20 mm to 1.00 mm; the wall thickness of the SiC composite outer shell is 0.25 mm to 2.00 mm.

[0011] In some embodiments, gaps are respectively left between the cladding and the fuel capsule, and between the SiC composite outer shell and the first fuel pellet.

[0012] In some embodiments, the width of the gap between the cladding and the fuel capsule is 0.05 mm to 0.20 mm.

[0013] In some embodiments, the gap width between the SiC composite material housing and the first fuel pellet is 0.05 mm to 0.20 mm.

[0014] In some embodiments, the accident tolerant fuel element further includes a metal layer, and the metal layer is liquid metal and / or metal foil; the metal layer is filled between the cladding and the fuel capsule, and / or between the SiC composite material housing and the first fuel pellet.

[0015] In some embodiments, in the fuel capsule, the number of the first fuel pellets loaded in the SiC composite material housing is 30 to 150.

[0016] In some embodiments, the cladding is a zirconium alloy cladding, an FeCrAl alloy cladding or an ODS-FeCrAl stainless steel cladding.

[0017] In some embodiments, the accident tolerant fuel element further includes a second fuel pellet encapsulated in the cladding; the second fuel pellet is located on at least one side of the fuel capsule.

[0018] For the accident tolerant fuel element of the present utility model, the fuel pellets are loaded by the SiC composite material to form a fuel capsule and assembled in the cladding. The SiC composite material has excellent high temperature strength and can contain the rapid deformation of the fuel pellets, thereby reducing the risk of cladding bulging, rupture and fuel relocation under LOCA accidents. After the reflood quenching of the LOCA accident, even if the cladding undergoes brittle fracture, the internal SiC composite material can still maintain integrity during the reflood quenching, thereby maintaining the encapsulation of the fuel pellets.

[0019] In addition, it can also reduce or mitigate the risk of fuel dispersion under RIA accidents, thereby reducing the consequences of the accidents.

[0020] For the accident tolerant fuel element of the present utility model, when applied in a water-cooled reactor, it generally reduces the risk of failure of the fuel element in the water-cooled reactor under severe accidents and improves the accident tolerance performance of the fuel element. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present utility model will be further described below in conjunction with the drawings and embodiments. In the drawings:

[0022] Figure 1 is a schematic radial cross-sectional structure diagram of the accident tolerant fuel element according to the first embodiment of the present utility model;

[0023] Figure 2 is a schematic axial cross-sectional structure diagram of the accident tolerant fuel element according to the first embodiment of the present utility model;

[0024] Figure 3It is a schematic diagram of the axial cross-sectional structure of the accident-resistant fuel element of the second embodiment of the utility model;

[0025] Figure 4 It is a schematic diagram of the axial cross-sectional structure of the accident-resistant fuel element of the third embodiment of the utility model;

[0026] Figure 5 It is a schematic diagram of the axial cross-sectional structure of the accident-resistant fuel element of the fourth embodiment of the utility model;

[0027] Figure 6 It is a schematic diagram of the axial cross-sectional structure of the accident-resistant fuel element of the fifth embodiment of the utility model. DETAILED DESCRIPTION

[0028] In order to have a clearer understanding of the technical features, purposes and effects of the present utility model, the specific implementation methods of the present utility model are now described in detail with reference to the accompanying drawings.

[0029] The accident-resistant fuel element of the utility model comprises a cladding and a fuel capsule encapsulated in the cladding. The fuel capsule is at least one, and two or more fuel capsules are arranged in the cladding along the axial direction of the cladding.

[0030] The fuel capsule may further include a sealed SiC composite shell and at least one first fuel pellet encapsulated in the SiC composite shell. The SiC composite shell is built into the cladding, does not face the problem of hydrothermal corrosion, does not need to set an environmental barrier coating, does not need to change the water chemical conditions of the reactor, reduces the difficulty of developing the SiC composite shell, and can put SiC materials with excellent accident resistance into use as soon as possible.

[0031] like Figure 1 - Figure 2 As shown, the accident-resistant fuel element according to the first embodiment of the present invention comprises a cladding 10 and at least one fuel capsule 20 encapsulated in the cladding 10 .

[0032] The cladding 10 may be a zirconium alloy cladding, or a FeCrAl alloy cladding, or an ODS-FeCrAl stainless steel cladding, and the like.

[0033] In this embodiment, each fuel capsule 20 includes a sealed SiC composite shell 21 and two first fuel pellets 22 loaded in the SiC composite shell 21. The first fuel pellets 22 are arranged along the axial direction of the cladding 10.

[0034] The SiC composite material shell 21 may further include a SiC composite material tube and at least one SiC end plug. The SiC end plug is fitted on the end of the SiC composite material tube to seal the end of the SiC composite material tube. When the SiC composite material tube is a tube body with one end open and one end closed, the open end of the SiC composite material tube is sealed by one SiC end plug. When the SiC composite material tube is a tube body with both ends open, the two open ends of the SiC composite material tube are sealed by two SiC end plugs.

[0035] The SiC composite material tube can be formed by winding SiC fibers, two-dimensional or three-dimensional weaving into a tube and then adding a SiC matrix. The method of adding the SiC matrix can be one or more of chemical vapor infiltration (CVI), nano transient eutectic phase sintering (NITE), precursor infiltration and pyrolysis (PIP), melt infiltration (MI), etc.

[0036] Since the SiC composite material tube is placed inside the cladding 10, pores are allowed to exist. There is no need to be completely dense or add a single ceramic SiC layer by chemical vapor deposition (CVD) to ensure the airtightness of the SiC composite material tube, which reduces the processing and manufacturing difficulty of the SiC composite material tube and enables the SiC composite material with excellent accident tolerance performance to be put into application as soon as possible. The SiC end plug can be connected to the end of the SiC composite material tube by means of threaded connection, solid-phase diffusion connection, glass-ceramic connection, SiC precursor connection, reaction sintering connection, liquid-phase sintering connection, etc., further reducing the processing and manufacturing difficulty of the SiC composite material tube.

[0037] In addition, according to the number of the first fuel pellets 22 loaded in the fuel capsule 20, the SiC composite material shell 21 can adopt a short-sized SiC composite material tube (short size ≤ 1 m, and the length can at least accommodate the height of one fuel pellet), without being processed into the long size of the fuel element (the long size often requires a processing length of about 4 m), further reducing the processing and manufacturing difficulty of the SiC composite material tube.

[0038] The first fuel pellet 22 is a substance containing uranium, plutonium, and / or thorium. Further, the first fuel pellet 22 is selected from one or more of UO2, MOX (UO2-PuO2), UN, UC, U3Si2, ThO2, PuO2, PuN, PuC, UB2.

[0039] The first fuel pellet 22 can be an annular pellet or a solid pellet in structure. To increase the fuel loading amount, the first fuel pellet 22 is preferably a solid pellet.

[0040] Inside the cladding 10, there are gaps respectively between the cladding 10 and the fuel capsule 20, and between the SiC composite material outer shell 21 and the first fuel pellet 22. As an option, the gap width between the cladding 10 and the fuel capsule 20 is 0.05 mm to 0.20 mm, preferably 0.10 mm; the gap width between the SiC composite material outer shell 21 and the first fuel pellet 22 is 0.05 mm to 0.20 mm, preferably 0.10 mm.

[0041] The wall thickness of the cladding 10 is 0.20 mm to 1.00 mm, preferably 0.25 mm. The wall thickness of the SiC composite material tube of the SiC composite material outer shell 21 is 0.25 mm to 2.00 mm, preferably 0.95 mm.

[0042] As Figure 3 shown, the accident tolerant fuel element of the second embodiment of the present invention includes a cladding 10 and at least one fuel capsule 20 encapsulated in the cladding 10.

[0043] The cladding 10 can be a zirconium alloy cladding, or can also be an FeCrAl alloy cladding or an ODS-FeCrAl stainless steel cladding, etc.

[0044] Each fuel capsule 20 includes a sealed SiC composite material outer shell 21 and one or more first fuel pellets 22 loaded in the SiC composite material outer shell 21. The first fuel pellets 22 are arranged along the axial direction of the cladding 10. In Figure 3 the shown embodiment, two first fuel pellets are encapsulated in at least one fuel capsule 20, and one first fuel pellet 22 is encapsulated in at least one fuel capsule 20.

[0045] The SiC composite material outer shell 21 may further include a SiC composite material tube and at least one SiC end plug. The SiC end plug is fitted on the end of the SiC composite material tube to close the end of the SiC composite material tube. When the SiC composite material tube is a tube body with one end open and one end closed, the open end of the SiC composite material tube is closed by one SiC end plug. When the SiC composite material tube is a tube body with both ends open, the two open ends of the SiC composite material tube are closed by two SiC end plugs.

[0046] The SiC composite material tube can be formed by winding SiC fibers and two-dimensional / three-dimensional braiding into a tube and then adding a SiC matrix. The adding method of the SiC matrix can adopt one or more of methods such as chemical vapor infiltration (CVI), nano transient eutectic phase sintering (NITE), precursor infiltration and pyrolysis (PIP), melt infiltration (MI), etc.

[0047] Since the SiC composite material tube is placed inside the cladding 10 and porosity is allowed, there is no need for it to be completely dense or have a single ceramic SiC layer by chemical vapor deposition (CVD) to ensure the airtightness of the SiC composite material tube, which reduces the manufacturing difficulty of the SiC composite material tube and enables the SiC composite material with excellent accident tolerance performance to be put into application as early as possible. The SiC end plug can be connected to the end of the SiC composite material tube by means such as threaded connection, solid-phase diffusion connection, glass-ceramic connection, SiC precursor connection, reaction sintering connection, and liquid-phase sintering connection, further reducing the manufacturing difficulty of the SiC composite material tube.

[0048] In addition, according to the number of the first fuel pellets 22 loaded in the fuel capsule 20, the SiC composite material outer shell 21 can adopt a short-sized SiC composite material tube (short size ≤ 1 m, and the length can at least accommodate the height of one fuel pellet), without the need to be processed into the long size of the fuel element (the long size often requires a processing length of about 4 m), further reducing the manufacturing difficulty of the SiC composite material tube.

[0049] The first fuel pellet 22 is a substance containing uranium, plutonium, and / or thorium. Further, the first fuel pellet 22 is selected from one or more of UO2, MOX (UO2-PuO2), UN, UC, U3Si2, ThO2, PuO2, PuN, PuC, and UB2.

[0050] The first fuel pellet 22 can be an annular pellet or a solid pellet in structure. To increase the fuel loading amount, the first fuel pellet 22 is preferably a solid pellet.

[0051] Inside the cladding 10, gaps are left between the cladding 10 and the fuel capsule 20, and between the SiC composite material outer shell 21 and the first fuel pellet 22 respectively. As an option, the gap width between the cladding 10 and the fuel capsule 20 is 0.05 mm to 0.20 mm, and 0.10 mm can be preferably selected; the gap width between the SiC composite material outer shell 21 and the first fuel pellet 22 is 0.05 mm to 0.20 mm, and 0.10 mm can be preferably selected.

[0052] The wall thickness of the cladding 10 is 0.20 mm to 1.00 mm, and 0.25 mm can be preferably selected. The wall thickness of the SiC composite material tube of the SiC composite material outer shell 21 is 0.25 mm to 2.00 mm, and 0.95 mm can be preferably selected.

[0053] As Figure 4 shown, the accident-tolerant fuel element of the third embodiment of the present invention includes a cladding 10 and at least one fuel capsule 20 encapsulated in the cladding 10.

[0054] The cladding 10 can be a zirconium alloy cladding, or an FeCrAl alloy cladding, an ODS-FeCrAl stainless steel cladding, etc. The fuel capsule 20 includes a sealed SiC composite outer shell 21 and at least one first fuel pellet 22 loaded inside the SiC composite outer shell 21.

[0055] In order to reduce the risk of the fuel capsule 20 scattering after the cladding 10 breaks and reduce the manufacturing cost of the fuel capsule 20, in this embodiment, the number of the first fuel pellets 22 loaded in the fuel capsule 20 is 30 to 150. The first fuel pellets 22 are arranged axially along the cladding 10 inside the fuel capsule 20.

[0056] The SiC composite outer shell 21 may further include a SiC composite tube and at least one SiC end plug. The SiC end plug is fitted on the end of the SiC composite tube to seal the end of the SiC composite tube. When the SiC composite tube is a tube body with one end open and one end closed, the open end of the SiC composite tube is sealed by one SiC end plug. When the SiC composite tube is a tube body with both ends open, the two open ends of the SiC composite tube are sealed by two SiC end plugs.

[0057] The SiC composite tube can be formed by winding SiC fibers, two-dimensional / three-dimensional braiding into a tube and then adding a SiC matrix. The method of adding the SiC matrix can be one or more of chemical vapor infiltration (CVI), nano-instant eutectic phase sintering (NITE), precursor infiltration and pyrolysis (PIP), melt infiltration (MI), etc.

[0058] Since the SiC composite tube is placed inside the cladding 10, pores are allowed to exist. There is no need to be completely dense or apply a single ceramic SiC layer by chemical vapor deposition (CVD) to ensure the airtightness of the SiC composite tube, which reduces the processing and manufacturing difficulty of the SiC composite tube and enables the SiC composite with excellent accident tolerance performance to be put into application as early as possible. The SiC end plug can be connected to the end of the SiC composite tube by means of threaded connection, solid-phase diffusion connection, glass-ceramic connection, SiC precursor connection, reaction sintering connection, liquid-phase sintering connection, etc., further reducing the processing and manufacturing difficulty of the SiC composite tube.

[0059] In addition, according to the number of the first fuel pellets 22 loaded in the fuel capsule 20, the SiC composite outer shell 21 can adopt a short-sized SiC composite tube (short size ≤ 1 m, and the length can at least accommodate the height of one fuel pellet), without being processed into the long size of the fuel element (the long size often requires a processing length of about 4 m), further reducing the processing and manufacturing difficulty of the SiC composite tube.

[0060] The first fuel pellet 22 is a substance containing uranium, plutonium, and / or thorium. Further, the first fuel pellet 22 is selected from one or more of UO2, MOX (UO2-PuO2), UN, UC, U3Si2, ThO2, PuO2, PuN, PuC, UB2.

[0061] The first fuel pellet 22 can be an annular pellet or a solid pellet in structure. To increase the fuel loading amount, the first fuel pellet 22 is preferably a solid pellet.

[0062] Inside the cladding 10, there are gaps respectively between the cladding 10 and the fuel capsule 20, and between the SiC composite material outer shell 21 and the first fuel pellet 22. As an option, the gap width between the cladding 10 and the fuel capsule 20 is 0.05 mm to 0.20 mm, and 0.10 mm can be preferably selected; the gap width between the SiC composite material outer shell 21 and the first fuel pellet 22 is 0.05 mm to 0.20 mm, and 0.10 mm can be preferably selected.

[0063] The wall thickness of the cladding 10 is 0.20 mm to 1.00 mm, and 0.25 mm can be preferably selected. The wall thickness of the SiC composite material tube of the SiC composite material outer shell 21 is 0.25 mm to 2.00 mm, and 0.95 mm can be preferably selected.

[0064] As Figure 5 shown, the accident-tolerant fuel element of the fourth embodiment of the present utility model includes a cladding 10 and at least one fuel capsule 20 encapsulated in the cladding 10.

[0065] The cladding 10 can be a zirconium alloy cladding, or can also be an FeCrAl alloy cladding or an ODS-FeCrAl stainless steel cladding, etc. The fuel capsule 20 includes a sealed SiC composite material outer shell 21 and at least one first fuel pellet 22 loaded in the SiC composite material outer shell 21.

[0066] The SiC composite material outer shell 21 can further include a SiC composite material tube and at least one SiC end plug. The SiC end plug is fitted on the end of the SiC composite material tube to seal the end of the SiC composite material tube. When the SiC composite material tube is a tube body with one end open and one end closed, the open end of the SiC composite material tube is sealed by one SiC end plug. When the SiC composite material tube is a tube body with both ends open, the two open ends of the SiC composite material tube are sealed by two SiC end plugs.

[0067] Since the SiC composite material tube is placed inside the cladding 10 and porosity is allowed, there is no need for it to be completely dense or have a single ceramic SiC layer deposited by chemical vapor deposition (CVD) to ensure the airtightness of the SiC composite material tube. This reduces the manufacturing difficulty of the SiC composite material tube, enabling the SiC composite material with excellent accident tolerance performance to be put into application earlier. The SiC end plug can be connected to the end of the SiC composite material tube by means such as threaded connection, solid-phase diffusion connection, glass-ceramic connection, SiC precursor connection, reaction sintering connection, and liquid-phase sintering connection, further reducing the manufacturing difficulty of the SiC composite material tube.

[0068] In addition, according to the number of the first fuel pellets 22 loaded in the fuel capsule 20, the SiC composite material outer shell 21 can adopt a short-sized SiC composite material tube (short size ≤ 1 m, and the length can at least accommodate the height of one fuel pellet), without the need to be processed into the long size of a fuel element (the long size often requires a processing length of about 4 m), further reducing the manufacturing difficulty of the SiC composite material tube.

[0069] The first fuel pellet 22 is a substance containing uranium, plutonium, and / or thorium. Further, the first fuel pellet 22 is selected from one or more of UO2, MOX (UO2 - PuO2), UN, UC, U3Si2, ThO2, PuO2, PuN, PuC, and UB2.

[0070] The first fuel pellet 22 can be an annular pellet or a solid pellet in structure. To increase the fuel loading amount, the first fuel pellet 22 is preferably a solid pellet.

[0071] Inside the cladding 10, gaps are left between the cladding 10 and the fuel capsule 20, and between the SiC composite material outer shell 21 and the first fuel pellet 22 respectively. As an option, the gap width between the cladding 10 and the fuel capsule 20 is 0.05 mm - 0.20 mm, and 0.10 mm can be preferably selected; the gap width between the SiC composite material outer shell 21 and the first fuel pellet 22 is 0.05 mm - 0.20 mm, and 0.10 mm can be preferably selected.

[0072] The wall thickness of the cladding 10 is 0.20 mm - 1.00 mm, and 0.25 mm can be preferably selected. The wall thickness of the SiC composite material tube of the SiC composite material outer shell 21 is 0.25 mm - 2.00 mm, and 0.95 mm can be preferably selected.

[0073] In this embodiment, the accident-tolerant fuel element further includes a metal layer 30, and the metal layer 30 is a liquid metal and / or a metal foil. The metal layer 30 is filled in at least one of the positions between the cladding 10 and the fuel capsule 20, and between the SiC composite material outer shell 21 and the first fuel pellet 22.

[0074] The liquid metal is formed from low melting point metals, and the low melting point metals are selected from one or more of tin, sodium, lead, bismuth, lithium, mercury, and zinc. The metal foil includes, but is not limited to, gold foil, silver foil, copper foil, aluminum foil, magnesium foil, tantalum foil, titanium foil, stainless steel foil, and the like.

[0075] Preferably, in this embodiment, a metal foil is filled between the cladding 10 and the fuel capsule 20, and a liquid metal is filled between the SiC composite material outer shell 21 and the first fuel pellet 22.

[0076] Furthermore, Figure 5 In the illustrated embodiment, the number of the first fuel pellets 22 loaded in the fuel capsule 20 is 30 to 150. The first fuel pellets 22 are arranged axially along the cladding 10 in the fuel capsule 20.

[0077] It can be understood that the fuel capsule 20 of this embodiment can also refer to the first to third embodiments, and one or more first fuel pellets 22 are loaded inside each fuel capsule 20.

[0078] Such as Figure 6 As shown, the accident tolerant fuel element of the fifth embodiment of the present utility model includes a cladding 10, at least one fuel capsule 20 encapsulated in the cladding 10, and further includes at least one second fuel pellet 40 encapsulated in the cladding 10.

[0079] The cladding 10 can be a zirconium alloy cladding, or can also be an FeCrAl alloy cladding or an ODS-FeCrAl stainless steel cladding, and the like. The fuel capsule 20 includes a sealed SiC composite material outer shell 21 and at least one first fuel pellet 22 loaded in the SiC composite material outer shell 21.

[0080] The SiC composite material outer shell 21 can further include a SiC composite material tube and at least one SiC end plug. The SiC end plug is fitted on the end of the SiC composite material tube to seal the end of the SiC composite material tube. When the SiC composite material tube is a tube body with one end open and one end closed, the open end of the SiC composite material tube is sealed by one SiC end plug. When the SiC composite material tube is a tube body with both ends open, the two open ends of the SiC composite material tube are sealed by two SiC end plugs.

[0081] Since the SiC composite material tube is placed inside the cladding 10 and porosity is allowed, there is no need for it to be completely dense or have a single ceramic SiC layer deposited by chemical vapor deposition (CVD) to ensure the airtightness of the SiC composite material tube, which reduces the manufacturing difficulty of the SiC composite material tube and enables the SiC composite material with excellent accident tolerance performance to be put into application earlier. The SiC end plug can be connected to the end of the SiC composite material tube by means such as threaded connection, solid-phase diffusion connection, glass-ceramic connection, SiC precursor connection, reaction sintering connection, and liquid-phase sintering connection, further reducing the manufacturing difficulty of the SiC composite material tube.

[0082] In addition, according to the number of the first fuel pellets 22 loaded in the fuel capsule 20, the SiC composite material outer shell 21 can adopt a short-sized SiC composite material tube (short size ≤ 1 m, and the length can at least accommodate the height of one fuel pellet), without the need to be processed into the long size of the fuel element (the long size often requires a processing length of about 4 m), further reducing the manufacturing difficulty of the SiC composite material tube.

[0083] The first fuel pellet 22 is a substance containing uranium, plutonium, and / or thorium. Further, the first fuel pellet 22 is selected from one or more of UO2, MOX (UO2-PuO2), UN, UC, U3Si2, ThO2, PuO2, PuN, PuC, UB2. The first fuel pellet 22 can be an annular pellet or a solid pellet in structure. To increase the fuel loading amount, the first fuel pellet 22 is preferably a solid pellet.

[0084] The number and arrangement form of the fuel capsule 20 and the first fuel pellets 22 inside it can refer to the above first to fourth embodiments and will not be elaborated here.

[0085] Inside the cladding 10, gaps are left between the cladding 10 and the fuel capsule 20, and between the SiC composite material outer shell 21 and the first fuel pellets 22 respectively. As an option, the gap width between the cladding 10 and the fuel capsule 20 is 0.05 mm to 0.20 mm, and 0.10 mm can be preferably selected; the gap width between the SiC composite material outer shell 21 and the first fuel pellets 22 is 0.05 mm to 0.20 mm, and 0.10 mm can be preferably selected. The wall thickness of the cladding 10 is 0.20 mm to 1.00 mm, and 0.25 mm can be preferably selected. The wall thickness of the SiC composite material tube of the SiC composite material outer shell 21 is 0.25 mm to 2.00 mm, and 0.95 mm can be preferably selected.

[0086] The second fuel pellets 40 are located on at least one side of the fuel capsule 20 inside the cladding 10.

[0087] The second fuel pellet 40 is a substance containing uranium, plutonium, and / or thorium. Further, the second fuel pellet 40 is selected from one or more of UO2, MOX (UO2-PuO2), UN, UC, U3Si2, ThO2, PuO2, PuN, PuC, UB2. The second fuel pellet 40 can be an annular pellet or a solid pellet in structure. To increase the fuel loading, the second fuel pellet 40 is preferably a solid pellet.

[0088] Specifically, in Figure 6 the illustrated embodiment, three first fuel pellets 22 are loaded in the fuel capsule 20. The second fuel pellets 40 are axially distributed on opposite sides of the fuel capsule 20 along the cladding 10.

[0089] Taking the cladding 10, the fuel capsule 20, and the second fuel pellet 40 all being circular as an example, the diameter of the second fuel pellet 40 is equal to the outer diameter of the fuel capsule 20. A gap is also left between the second fuel pellet 40 and the cladding 10, and the gap distance is 0.05 mm to 0.20 mm, and 0.10 mm can be preferably selected.

[0090] According to requirements, in this embodiment, a metal layer can also be respectively provided between the cladding 10 and the fuel capsule 20, between the SiC composite outer shell 21 and the first fuel pellet 22, and between the cladding 10 and the second fuel pellet 40. The metal layer is a liquid metal and / or a metal foil.

[0091] In summary, for the accident tolerant fuel element of the present utility model, when the cladding is a zirconium alloy cladding, it is applicable to a water-cooled reactor; when the cladding is an FeCrAl alloy cladding or an ODS-FeCrAl stainless steel cladding, etc., it is applicable to a sodium-cooled fast reactor and a lead / lead-bismuth cooled fast reactor.

[0092] The above are only the embodiments of the present utility model, and do not limit the patent scope of the present utility model accordingly. Any equivalent structure or equivalent process transformation made by using the specification and drawings of the present utility model, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present utility model.

Claims

1. An accident-tolerant fuel element, characterized in that, It includes a cladding and at least one fuel capsule encapsulated within the cladding; The fuel capsule includes a sealed SiC composite material outer shell and at least one first fuel pellet loaded within the SiC composite material outer shell; A gap is respectively left between the cladding and the fuel capsule, and between the SiC composite material outer shell and the first fuel pellet.

2. The accident tolerant fuel element according to claim 1, characterized in that, The SiC composite material outer shell includes a SiC composite material tube and at least one SiC end plug; the SiC end plug closes the end of the SiC composite material tube.

3. The accident tolerant fuel element according to claim 1, characterized in that, The first fuel pellet is a solid pellet.

4. The accident-tolerant fuel element according to claim 1, characterized in that, The wall thickness of the cladding is 0.20 mm to 1.00 mm; the wall thickness of the SiC composite material outer shell is 0.25 mm to 2.00 mm.

5. The accident tolerant fuel element according to claim 1, characterized in that, The width of the gap between the cladding and the fuel capsule is 0.05 mm to 0.20 mm; The width of the gap between the SiC composite material outer shell and the first fuel pellet is 0.05 mm to 0.20 mm.

6. The accident tolerant fuel element according to claim 1, characterized in that, The accident tolerant fuel element further includes a metal layer, and the metal layer is liquid metal and / or metal foil; The metal layer is filled between the cladding and the fuel capsule, and / or between the SiC composite material outer shell and the first fuel pellet.

7. The accident-tolerant fuel element according to claim 1, characterized in that, In the fuel capsule, the number of the first fuel pellets loaded within the SiC composite material outer shell is 30 to 150.

8. The accident tolerant fuel element according to any one of claims 1-7, characterized in that, The cladding is a zirconium alloy cladding, an FeCrAl alloy cladding or an ODS-FeCrAl stainless steel cladding.

9. The accident tolerant fuel element according to any one of claims 1-7, characterized in that, The accident tolerant fuel element further includes a second fuel pellet encapsulated within the cladding; the second fuel pellet is located at at least one side of the fuel capsule.

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