Water cooled reactor fuel rod

Abstract

The application discloses a water-cooled reactor fuel rod, which comprises a cladding tube, upper and lower end plugs matched at opposite ends of the cladding tube, and fuel pellets stacked in the cladding tube; the fuel pellets comprise at least one first pellet; the first pellet is formed by at least two pellet monomers in the circumferential direction, and a through hole penetrating through opposite ends of the first pellet is formed on the first pellet, and the through hole is filled with a burnable poison nuclide filler. The water-cooled reactor fuel rod can absorb the gas generated by the pellet during the operation of the reactor, reduce the internal pressure of the cladding tube, reduce the failure risk of the fuel rod, avoid the leakage of radioactive substances, improve the utilization rate of uranium, and has a larger design margin.

Description

Technical Field

[0001] This invention relates to the field of nuclear power fuel assembly technology, and more particularly to a water-cooled reactor fuel rod. Background Technology

[0002] Rod-shaped fuel elements are currently the most widely used and mature type of fuel element in commercial reactors. However, factors affecting fuel reliability can exist during fuel manufacturing, transportation, hoisting, and in-reactor operation, leading to fuel failure (fuel rod breakage, loss of integrity) during in-reactor operation. Fuel failure can result in the leakage of radioactive fission products. To reduce the risks of fuel failure and fission product leakage, it is necessary to design a fuel element with higher design margins, improved fuel reliability, and minimized fission product leakage. Furthermore, with the increasing economic requirements of nuclear power plants for fuel cycles, improving uranium utilization and increasing cycle length have become increasingly important issues and are among the main directions for current fuel improvement.

[0003] Existing fuel elements, such as the rod-shaped fuel element disclosed in CN115938614A, improve fuel service temperature and reliability by modifying the cladding structure (setting ribs on the outer surface of the cladding). However, the ribbed structure on the outer surface of the cladding allows heat released from the fuel rod to easily accumulate in the area where the fuel rod contacts the ribs. In the event of accidents such as flow blockage, the temperature may rise sharply, affecting fuel reliability. Furthermore, the fuel core is coated with a multi-layered pyrolytic carbon structure, involving surface treatment operations that may affect the thermal properties of the fuel core and increase the complexity and difficulty of fuel manufacturing.

[0004] For example, CN114944234A discloses an integrated end-plug cladding annular fuel rod and fuel assembly. The fuel rod consists of an outer cladding, an inner cladding, and a core. One end of the outer cladding has an integrally formed upper end plug, and one end of the inner cladding has an integrally formed lower end plug. The core is stacked between the outer and inner claddings, and the outer and inner claddings are welded together to form a sealed chamber. This patent uses two integrated cladding-end-plug structures to form a sealed chamber. This design is suitable for annular fuel elements where coolant flows both inside and outside the fuel rod. However, the fuel core is relatively thin, and the uranium loading is limited, which is not conducive to increasing the fuel cycle length. In addition, this design increases the requirements for the coolant flow field, and the requirements for the fuel element design will also increase accordingly. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a water-cooled reactor fuel rod that reduces the risk of fuel rod failure and avoids the leakage of radioactive materials.

[0006] The technical solution adopted by the present invention to solve its technical problem is: to provide a water-cooled reactor fuel rod, including a cladding tube, an upper end plug and a lower end plug fitted at opposite ends of the cladding tube, and fuel pellets stacked inside the cladding tube;

[0007] The fuel pellet includes at least one first pellet; the first pellet is formed by at least two pellet units surrounding each other in the circumferential direction, and the first pellet has through holes extending through its opposite ends, the through holes being filled with a filler containing a combustible toxic nuclide.

[0008] Preferably, the filler containing combustible poison nuclides is loose, porous pyrolytic carbon and contains... 10 B 157 Gd or 167 A mixture of Er oxides, or a loose, porous pyrolytic carbon containing... 10 B 157 Gd or 167 A mixture of Er carbides, or including at least one of loosely porous boron carbide, gadolinium carbide, and zirconium boride.

[0009] Preferably, the total stacking height of the fuel pellets is 500mm to 4500mm; the stacking height of the first pellet is 500mm to 4000mm.

[0010] Preferably, the outer diameter of the first core block is 4.5mm to 9mm, and the inner diameter is 0.2mm to 2mm; the ratio of the height to the outer diameter of the first core block is 1.0 to 1.4.

[0011] Preferably, the first core is made of uranium oxides, nitrides and / or carbides; the enrichment of the first core is 2% to 10%.

[0012] Preferably, the fuel pellet further includes at least one solid second pellet;

[0013] The second core block is stacked inside the casing tube on at least one side of the first core block.

[0014] Preferably, the outer diameter of the second core block is 4.5mm to 9mm; the ratio of the height to the outer diameter of the second core block is 1.0 to 1.4.

[0015] Preferably, the second core is made of uranium oxides, nitrides, and / or carbides; the enrichment of the second core is 2% to 10%.

[0016] Preferably, the end periphery of the second core block is provided with a rounded chamfer; and / or, at least one end face of the second core block is provided with a disc-shaped concave portion.

[0017] Preferably, the fuel pellet comprises a plurality of first pellets and at least two second pellets;

[0018] Multiple first core blocks are stacked sequentially in the middle of the casing tube, with at least two core blocks respectively disposed between the first core block and the upper end plug, and between the first core block and the lower end plug.

[0019] Preferably, an air gap is provided between the fuel pellet and the cladding tube, and the width of the air gap is 0.05 mm to 0.2 mm.

[0020] Preferably, the casing tube is filled with helium gas at a pressure of 0.1 MPa to 6 MPa.

[0021] Preferably, the lower end plug is integrally formed with the casing tube.

[0022] Preferably, the water-cooled reactor fuel rods further include cavity springs, which are disposed inside the cladding tube and abut against the upper end plug and the fuel pellet.

[0023] Preferably, the length of the water-cooled reactor fuel rods is 1000mm to 5000mm.

[0024] The beneficial effects of this invention are: by providing holes in the pellets and filling them with filler containing combustible poison nuclides, it is possible to absorb the gas generated by the pellets during reactor operation, reduce the internal pressure of the cladding tubes, reduce the risk of fuel rod failure, avoid leakage of radioactive materials, improve uranium utilization, and have a greater design margin. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0026] Figure 1 This is a schematic diagram of the longitudinal cross-sectional structure of a water-cooled reactor fuel rod according to an embodiment of the present invention;

[0027] Figure 2 yes Figure 1 A schematic diagram of the structure of the first core block;

[0028] Figure 3 This is a schematic diagram of the structure of the second core block in the cladding tube of a water-cooled reactor fuel rod according to an embodiment of the present invention. Detailed Implementation

[0029] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0030] like Figure 1As shown, a water-cooled reactor fuel rod according to an embodiment of the present invention may include a cladding tube 100, an upper end plug 110 and a lower end plug 120 fitted at opposite ends of the cladding tube, and fuel pellets stacked inside the cladding tube 100.

[0031] The upper plug 110 can be fixedly connected to the upper end of the casing tube 100 by welding or other means to close the upper opening of the casing tube 100. The lower plug 120 can also be fixedly connected to the lower end of the casing tube 100 by welding or other means to close the lower opening, thereby forming a sealed chamber inside the casing tube 100.

[0032] Preferably, the lower plug 120 is integrally formed with the cladding tube 100, which reduces the number of welds on the fuel rods and lowers the risk of fuel failure due to weld defects. Furthermore, during reactor operation, fuel rods may sit on the bottom and come into contact with the bottom structure of the fuel elements; under the scouring of water flow, the lower plug of the fuel rods may erode. The lower plug 120, designed integrally with the cladding tube 100, is a solid structure from its upper surface to its lower end, providing better erosion resistance. Moreover, due to the absence of weld-affected areas, it offers a larger erosion space compared to the traditional welded design of the fuel rod cladding tube and lower plug, providing a greater safety margin.

[0033] In one embodiment, the outer diameter of the cladding tube 100 is 6 mm to 10 mm, and the wall thickness is 0.5 mm to 0.7 mm.

[0034] The cladding tube 100 can be made of Zr alloy, SiC or stainless steel. The upper plug 110 and the lower plug 120 can each be made of Zr alloy, SiC or stainless steel.

[0035] Fuel pellets are stacked axially within the cladding tube 100. An air gap, 0.05 mm to 0.2 mm wide, is maintained between the fuel pellets and the cladding tube 100. Helium gas is filled within the cladding tube 100, including the air gap, and the helium pressure is controlled to be between 0.1 MPa and 6 MPa.

[0036] Specifically, the fuel pellet includes at least one first pellet 10. The first pellet 10 has through holes extending through its opposite ends, and the through holes are filled with a filler 30 containing a combustible poison nuclide.

[0037] In this invention, the through-holes on the first fuel pellet 10 increase the internal cavity volume of the fuel rod, thereby reducing the internal pressure, lowering the center temperature of the pellet, and improving the axial power distribution. This also reduces the risk of pellet meltdown, improves the fuel's PCI resistance, provides a greater safety margin, and ultimately achieves deeper burnup. By filling the through-holes with a combustible poison nuclide-containing material 30, radioactive fission gases generated by the pellets can be absorbed during reactor operation, reducing the internal pressure of the cladding and preventing leakage of radioactive materials. Furthermore, the combustible poison nuclides contained in the filler material 30 can flatten the neutron flux distribution of the fuel rods, further providing better control over the rod power distribution, maximizing fuel utilization, and reducing fuel cycle costs.

[0038] In the 30 fillers containing flammable poison nuclides, the flammable poison nuclides include 10 B 157 Gd and 167 Er. In this regard, the filler 30 containing combustible poison nuclides can be macroscopically loose and porous pyrolytic carbon and containing... 10 B 157 Gd or 167 A mixture of Er oxides, or macroscopically loose and porous pyrolytic carbon and containing 10 B 157 Gd or 167 A mixture of Er carbides, or including at least one of macroscopically loose and porous boron carbide, macroscopically loose and porous gadolinium carbide, and macroscopically loose and porous zirconium boride.

[0039] To reduce the difficulty of controlling the through-hole size during the manufacturing process of the first core block 10, the first core block 10 can be formed by connecting at least two core block units 11 in the circumferential direction. For example, as Figure 2 As shown, the first core block 10 has a cylindrical structure, comprising two semi-annular core block units 11, which are joined together, with a through hole formed between the inner surfaces of the two core block units 11. In other embodiments, the first core block 10 may also include three or more core block units 11, which are fan-shaped, and multiple core block units 11 are joined sequentially to form the integral first core block 10, with a through hole formed between the opposing inner surfaces of the multiple core block units 11.

[0040] The first core block 10 is formed by splicing core block individual units 11. Compared with the integral cylindrical core block with a central hole, the core block individual unit 11 is easier to press and grind, which facilitates the size correction of the core block after sintering. It can effectively and accurately control the shape, size and density of the core block, and reduce the risk of core block falling off and not being able to be ground during the grinding process after the core block is sintered.

[0041] The first core block 10 can be configured similarly to a conventional solid core block in terms of size and material. However, compared to a solid core block, the through-holes in the first core block 10 make it an annular core block with a certain wall thickness. For multiple first core blocks 10, the sizes of the through-holes can be the same or different; with different through-hole sizes, the filling amount of the combustible poison nuclide filler 30 can vary. In terms of size, the outer diameter of the first core block 10 is 4.5 mm to 9 mm, and the inner diameter is 0.2 mm to 2 mm; the height-to-outer diameter ratio of the first core block 10 is 1.0 to 1.4. In terms of material, the first core block 10 can be made of uranium oxides, nitrides, and / or carbides; the enrichment degree of the first core block 10 is 2% to 10%.

[0042] Inside the cladding tube 100, the total stacking height of the fuel pellets is 500mm to 4500mm, wherein the stacking height of the first pellet 10 can be 500mm to 4000mm.

[0043] The first pellet 10 has rounded chamfers at its two ends, which can reduce the risk of the first pellet 10 falling off due to transportation or vibration after it is installed in the cladding tube 100. It can also reduce the stress on the cladding tube 100 when the first pellet 10 comes into contact with the cladding tube 100 after it swells due to irradiation during operation in the reactor, thus reducing the risk of fuel PCI failure and providing a larger design margin.

[0044] To obtain better axial power distribution in the fuel rods and core, the first pellet 10 can have different fuel enrichment and different through-hole sizes at different axial heights of the fuel rods.

[0045] exist Figure 1 In the illustrated embodiment, the fuel pellet further includes at least one solid second pellet 20. The second pellet 20 is stacked within the casing tube 100 on at least one side of the first pellet 10, preferably with the first pellet 10 located in the middle of the casing tube 100. In a preferred embodiment, the fuel pellet includes a plurality of first pellets 10 and at least two second pellets 20; the plurality of first pellets 10 are stacked sequentially in the middle of the casing tube 100, and at least two second pellets 20 are respectively disposed between the first pellet 10 and the upper plug 110, and between the first pellet 10 and the lower plug 120. For example, at least one second pellet 20 is located between the first pellet 10 and the upper plug 110, and at least one second pellet 20 is located between the first pellet 10 and the lower plug 120.

[0046] In other embodiments, the fuel pellets may also be formed entirely by stacking the first pellets 10. Alternatively, a plurality of first pellets 10 may be stacked within the casing tube 100, with at least one second pellet 20 disposed between the first pellets 10 and the upper plug 110. Or, a plurality of first pellets 10 may be stacked within the casing tube 100, with at least one second pellet 20 disposed between the first pellets 10 and the lower plug 120.

[0047] In terms of size and material, the second core 20 may be identical to the first core 10. For example, the outer diameter of the second core 20 is 4.5 mm to 9 mm; the height-to-outer-diameter ratio of the second core 20 is 1.0 to 1.4. The second core 20 may be made of uranium oxides, nitrides, and / or carbides; the enrichment of the second core 20 is 2% to 10%.

[0048] Understandably, the enrichment levels of the first core 10 and the second core 20 can be the same or different. Similarly, the enrichment levels of the first core 10 and the second core 20 can be the same or different. In fuel rods, higher enrichment or higher density fuel can increase the uranium load to improve neutron economy.

[0049] To obtain better axial power distribution in the fuel rods and core, the first core block 10 and the second core block 20 can have different fuel enrichment at different axial heights of the fuel rods.

[0050] Combination Figure 1 and Figure 3 The second pellet 20 has rounded chamfers 21 at its two ends, which can reduce the risk of the second pellet 20 falling off due to transportation or vibration after it is installed in the cladding tube 100. It can also reduce the stress on the cladding tube 100 when the second pellet 20 comes into contact with the cladding tube 100 after irradiation swelling during operation in the reactor, reduce the risk of fuel PCI failure, and provide a larger design margin.

[0051] The second core block 20 has a dish-shaped recess 22 at the center of at least one end face, which allows for greater axial expansion at the core block centerline and increases the cavity volume for accommodating the release of fission gas. Figure 3 As shown, the two opposite ends of the second core block 20 are respectively provided with disc-shaped recesses 22. When the two second core blocks 20 are stacked one on top of the other, their opposite ends fit together, and the disc-shaped recesses 22 on the two ends face each other to form a cavity that is wide in the center and flat at the periphery.

[0052] Furthermore, the water-cooled reactor fuel rods of the present invention also include a cavity spring 40, which is disposed inside the cladding tube 100 and abuts against the upper end plug 110 and the fuel pellet, thereby preventing the fuel pellet from axially moving inside the cladding tube 100.

[0053] Hollow springs 40 are typically made of stainless steel.

[0054] In a preferred embodiment of the water-cooled reactor fuel rods of the present invention, the overall length (axial length) of the water-cooled reactor fuel rods is 1000 mm to 5000 mm. For this length, the total stacking height of the fuel pellets is 500 mm to 4500 mm.

[0055] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A water-cooled reactor fuel rod, characterized in that, Includes a casing tube, upper and lower end plugs fitted at opposite ends of the casing tube, and fuel pellets stacked inside the casing tube; The fuel pellet includes at least one first pellet; the first pellet is formed by circumferentially connecting at least two pellet units, and a through-hole is formed on the first pellet through its opposite ends, the through-hole being formed between the inner surfaces of the pellet units; the through-hole is filled with a filler containing a combustible poison nuclide to absorb radioactive fission gases produced by the pellet during reactor operation; the filler containing the combustible poison nuclide is loosely porous pyrolytic carbon and a mixture containing... 10 B 157 Gd or 167 A mixture of Er oxides, or a loose, porous pyrolytic carbon containing... 10 B 157 Gd or 167 A mixture of Er carbides, or including at least one of loosely porous boron carbide, gadolinium carbide, and zirconium boride.

2. The water-cooled reactor fuel rods according to claim 1, characterized in that, The total stacking height of the fuel pellets is 500mm to 4500mm; the stacking height of the first pellet is 500mm to 4000mm.

3. The water-cooled reactor fuel rods according to claim 1, characterized in that, The outer diameter of the first core block is 4.5mm to 9mm, and the inner diameter is 0.2mm to 2mm; the ratio of the height to the outer diameter of the first core block is 1.0 to 1.

4.

4. The water-cooled reactor fuel rods according to claim 1, characterized in that, The first pellet is made of uranium oxides, nitrides and / or carbides; the enrichment of the first pellet is 2% to 10%.

5. The water-cooled reactor fuel rods according to claim 1, characterized in that, The fuel pellet also includes at least one solid second pellet; The second core block is stacked inside the casing tube on at least one side of the first core block.

6. The water-cooled reactor fuel rods according to claim 5, characterized in that, The outer diameter of the second core block is 4.5mm to 9mm; the ratio of the height to the outer diameter of the second core block is 1.0 to 1.

4.

7. The water-cooled reactor fuel rods according to claim 5, characterized in that, The second core is made of uranium oxides, nitrides and / or carbides; the enrichment of the second core is 2% to 10%.

8. The water-cooled reactor fuel rods according to claim 5, characterized in that, The second core block has a rounded chamfer at its end periphery; and / or, at least one end face of the second core block has a disc-shaped concave portion at its center.

9. The water-cooled reactor fuel rods according to claim 5, characterized in that, The fuel pellets include a plurality of first pellets and at least two second pellets; Multiple first core blocks are stacked sequentially in the middle of the casing tube, and at least two second core blocks are respectively disposed between the first core block and the upper end plug, and between the first core block and the lower end plug.

10. The water-cooled reactor fuel rods according to any one of claims 1 to 9, characterized in that, An air gap is left between the fuel pellet and the cladding tube, and the width of the air gap is 0.05mm to 0.2mm.

11. The water-cooled reactor fuel rods according to any one of claims 1 to 9, characterized in that, The cladding tube is filled with helium gas at a pressure of 0.1 MPa to 6 MPa.

12. The water-cooled reactor fuel rods according to any one of claims 1 to 9, characterized in that, The lower end plug is integrally formed with the casing tube.

13. The water-cooled reactor fuel rods according to any one of claims 1 to 9, characterized in that, The water-cooled reactor fuel rods also include cavity springs, which are disposed inside the cladding tube and abut against the upper plug and the fuel pellet.

14. The water-cooled reactor fuel rods according to any one of claims 1 to 9, characterized in that, The length of the fuel rods in the water-cooled reactor is 1000mm to 5000mm.

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