Fuel rod for water-cooled reactor

Abstract

Disclosed in the present invention is a fuel rod for a water-cooled reactor. The fuel rod comprises a cladding tube, an upper end plug and a lower end plug that match at two opposite ends of the cladding tube, and fuel pellets stacked in the cladding tube, wherein the fuel pellets comprise at least one first pellet; the first pellet is formed by at least two pellet units connected in an enclosed manner in a circumferential direction; and a through hole penetrating two opposite ends of the first pellet is formed in the first pellet, and is filled with a filler containing burnable poison nuclides. In the fuel rod for a water-cooled reactor of the present invention, by means of providing a hole in a pellet and filling the hole with the filler containing the burnable poison nuclides, a gas generated by the pellet during the operation of the reactor can be absorbed, thereby reducing the internal pressure of the cladding tube, reducing the risk of fuel rod failure, preventing the leakage of radioactive substances, increasing the uranium utilization rate, and providing a relatively large design margin.

Description

Water-cooled reactor fuel rods Technical Field

[0001] The present invention relates to the technical field of nuclear power fuel assemblies, and in particular to a water-cooled reactor fuel rod. Background Art

[0002] Rod-shaped fuel elements are the most widely used and mature type of fuel element in current commercial reactors. However, factors can affect fuel reliability during fuel fabrication, transportation, hoisting, and in-reactor operation, leading to fuel failure (fuel rod breakage and loss of integrity) during in-reactor operation. Fuel failure can lead to the leakage of radioactive fission products. To mitigate the risks of fuel failure and fission product leakage, it is necessary to design fuel elements with higher design margins, improve fuel reliability, and minimize fission product leakage. Furthermore, as nuclear power plants increase their fuel cycle economics, improving uranium utilization and increasing cycle length are becoming increasingly important issues and are currently one of the main directions for fuel improvement.

[0003] Existing fuel elements, such as the rod-shaped fuel element disclosed in CN115938614A, improve the fuel's service temperature and reliability by modifying the cladding structure (ribs are provided on the outer surface of the cladding). However, this ribbed cladding structure easily accumulates heat released by the fuel rod in the contact area with the ribs. In the event of a flow blockage or other incident, the temperature may rise sharply, affecting the fuel's reliability. Furthermore, the fuel core is coated with a multi-layer pyrolytic carbon structure, which requires surface treatment of the fuel core, potentially affecting its thermal properties and increasing the complexity and difficulty of fuel manufacturing.

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

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

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

[0007] The fuel pellets include at least one first pellet; the first pellet is formed by circumferentially surrounding at least two pellet monomers, and the first pellet is formed with through holes penetrating opposite ends thereof, and the through holes are filled with a filler containing a combustible poison nuclide.

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

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

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

[0011] Preferably, the first pellet is made of uranium oxide, nitride and / or carbide; and the enrichment of the first pellet is 2% to 10%.

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

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

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

[0015] Preferably, the second pellets are made of uranium oxide, nitride and / or carbide; and the enrichment of the second pellets is 2% to 10%.

[0016] Preferably, the periphery of the end of the second core block is provided with an arc chamfer; and / or, the middle portion of at least one end surface of the second core block is provided with a dish-shaped recess.

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

[0018] A plurality of the first core blocks are stacked in sequence in the middle of the cladding tube, and at least two of the core blocks are respectively arranged 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 left 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 cladding tube is filled with helium at a pressure of 0.1 MPa to 6 MPa.

[0021] Preferably, the lower end plug and the cladding tube are integrally formed.

[0022] Preferably, the water-cooled reactor fuel rod further comprises a cavity spring, which is disposed in the cladding tube and abuts between the upper end plug and the fuel pellet.

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

[0024] The beneficial effects of the present invention are as follows: by providing holes in the pellets and filling them with fillers containing combustible poison nuclides, the gas generated by the pellets during reactor operation can be absorbed, the internal pressure of the cladding tube can be reduced, the risk of fuel rod failure can be reduced, the leakage of radioactive materials can be avoided, the uranium utilization rate can be improved, and a larger design margin can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0026] FIG1 is a schematic diagram of a longitudinal cross-sectional structure of a water-cooled reactor fuel rod according to an embodiment of the present invention;

[0027] FIG2 is a schematic structural diagram of the first core block in FIG1 ;

[0028] FIG3 is a schematic structural diagram of a second pellet in a water-cooled reactor fuel rod in a cladding tube according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0030] As shown in FIG1 , 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 within the cladding tube 100 .

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

[0032] Preferably, the lower end plug 120 is integrally formed with the cladding tube 100. This reduces the number of welds on the fuel rods and lowers the risk of fuel failure due to weld defects. Furthermore, during reactor operation, the fuel rods may bottom out and contact the bottom structure of the fuel element. Under water flow, the lower end plugs of the fuel rods may corrode. The lower end plug 120, designed as an integral part of the cladding tube 100, is a solid structure from its upper surface to its lower end, offering improved abrasion resistance. Furthermore, since there is no weld-affected area, it provides a larger abrasion margin compared to conventional welded fuel rod cladding tube and lower end plug designs, 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 end plug 110 and the lower end plug 120 can each be made of Zr alloy, SiC or stainless steel.

[0035] The fuel pellets are stacked axially within the cladding tube 100. An air gap of 0.05 mm to 0.2 mm is left between the fuel pellets and the cladding tube 100. To account for this air gap, the cladding tube 100 is filled with helium, which fills the entire space within the cladding tube 100, including the air gap. The helium pressure is controlled between 0.1 MPa and 6 MPa.

[0036] Specifically, the fuel pellets include at least one first pellet 10. The first pellet 10 is formed with through holes penetrating opposite ends thereof, and the through holes are filled with a filler 30 containing a burnable poison nuclide.

[0037] In the present invention, the provision of through-holes in the first pellet 10 can expand the volume of the fuel rod's internal cavity, thereby reducing rod internal pressure, lowering the pellet's center temperature, and improving the rod's axial power distribution. It can also reduce the risk of pellet melt, enhance the fuel's resistance to PCI, provide a greater safety margin for the fuel, and achieve a deeper burnup. By providing a burnable poison nuclide filler 30 within the through-hole, radioactive fission gases generated by the pellet can be absorbed during reactor operation, reducing internal cladding pressure and preventing leakage of radioactive material. Furthermore, the burnable poison nuclides contained in the burnable poison nuclide filler 30 can flatten the fuel rod's neutron flux distribution, further improving rod power distribution control capabilities, maximizing fuel utilization, and reducing fuel cycle costs.

[0038] In the filler 30 containing burnable poison nuclides, the burnable 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 a macroscopic loose porous pyrolytic carbon and 10 B. 157 Gd or 167 A mixture of Er carbides, or 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 at least two core block monomers 11 connected in a circumferential direction. For example, as shown in Figure 2, the first core block 10 has a cylindrical structure and includes two semi-annular core block monomers 11, which are connected to each other, and the through-hole is formed between the inner surfaces of the two core block monomers 11. In other embodiments, the first core block 10 can also include three or more core block monomers 11, each of which is fan-shaped. Multiple core block monomers 11 are sequentially connected to form the entire first core block 10, and the through-hole is formed between the inner surfaces of the multiple core block monomers 11 facing each other.

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

[0041] The dimensions and materials of the first pellet 10 can be similar to those of conventional solid pellets. Compared to solid pellets, the through-holes in the first pellet 10 create an annular shape with a defined wall thickness. The through-holes in multiple first pellets 10 can be of the same or different sizes. With different through-hole sizes, the amount of the burnable poison nuclide filler 30 can vary. The outer diameter of the first pellet 10 ranges from 4.5 mm to 9 mm, and the inner diameter ranges from 0.2 mm to 2 mm. The ratio of the height to the outer diameter of the first pellet 10 ranges from 1.0 to 1.4. The first pellet 10 can be made of uranium oxide, nitride, and / or carbide. The enrichment of the first pellet 10 ranges from 2% to 10%.

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

[0043] Arc-shaped chamfers are provided on the periphery of the two opposite ends of the first pellet 10, which can reduce the risk of the first pellet 10 falling off due to transportation or vibration after being installed in the cladding tube 100. It can also reduce the stress applied to the cladding tube 100 when the first pellet 10 swells due to irradiation during operation in the reactor and contacts the cladding tube 100, thereby reducing the risk of PCI failure of the fuel and providing a larger design margin.

[0044] In order to obtain better axial power distribution of the fuel rod and the core, the first pellets 10 at different axial heights of the fuel rod may have different fuel enrichments and different through-hole sizes.

[0045] In the embodiment shown in Figure 1 , the fuel pellet further includes at least one solid second pellet 20. The second pellet 20 is stacked on at least one side of the first pellet 10 within the cladding tube 100, preferably with the first pellet 10 located in the center of the cladding 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 center of the cladding tube 100, and the at least two second pellets 20 are disposed between the first pellet 10 and the upper end plug 110, and between the first pellet 10 and the lower end plug 120, respectively. For example, at least one second pellet 20 is located between the first pellet 10 and the upper end plug 110, and at least one second pellet 20 is located between the first pellet 10 and the lower end plug 120.

[0046] In other embodiments, the fuel pellets may be entirely stacked from first pellets 10. Alternatively, multiple first pellets 10 may be stacked within the cladding tube 100, with at least one second pellet 20 disposed between the first pellets 10 and the upper end plug 110. Alternatively, multiple first pellets 10 may be stacked within the cladding tube 100, with at least one second pellet 20 disposed between the first pellets 10 and the lower end plug 120.

[0047] The second pellet 20 can be identical in size and material to the first pellet 10. For example, the outer diameter of the second pellet 20 is 4.5 mm to 9 mm, and the ratio of its height to outer diameter is 1.0 to 1.4. The second pellet 20 can be made of uranium oxide, nitride, and / or carbide, and have an enrichment of 2% to 10%.

[0048] It is understood that the enrichment levels of the first pellets 10 and the second pellets 20 can be the same or different. The enrichment levels of the first pellets 10 can be the same or different; the enrichment levels of the second pellets 20 can be the same or different. In fuel rods, higher-enrichment fuel or higher-density fuel can increase the uranium loading and improve neutron economy.

[0049] In order to obtain better axial power distribution of the fuel rod and the core, the first pellets 10 and the second pellets 20 at different axial heights of the fuel rod may have different fuel enrichments.

[0050] 1 and 3 , arc-shaped chamfers 21 are provided on the peripheries of the two opposite ends of the second pellet 20. This can reduce the risk of the second pellet 20 falling off due to transportation or vibration after being loaded into the cladding tube 100. It can also reduce the stress exerted on the cladding tube 100 by the second pellet 20 when it contacts the cladding tube 100 after swelling due to irradiation during operation in the reactor, thereby reducing the risk of PCI failure of the fuel and providing a larger design margin.

[0051] A disc-shaped recess 22 is provided in the middle of at least one end surface of the second pellet block 20. This allows for greater axial expansion of the pellet centerline and increases the volume of the cavity for accommodating fission gas release. As shown in Figure 3, disc-shaped recesses 22 are provided on opposite end surfaces of the second pellet block 20. When two second pellet blocks 20 are stacked one on top of the other, their opposing end surfaces mate, and the disc-shaped recesses 22 on the two end surfaces face each other, forming a cavity with a wide center and a flat periphery.

[0052] Furthermore, the water-cooled reactor fuel rod of the present invention further includes a cavity spring 40 , which is disposed in the cladding tube 100 and abuts between the upper end plug 110 and the fuel pellets, thereby preventing the fuel pellets from axially moving in the cladding tube 100 .

[0053] The cavity spring 40 is generally made of stainless steel.

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

[0055] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention's description and drawings, 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 water-cooled reactor fuel rod, characterized in that: It includes a cladding tube, an upper end plug and a lower end plug fitted at opposite ends of the cladding tube, and fuel pellets stacked in the cladding tube; The fuel core block includes at least one first core block; the first core block is formed by at least two core block monomers connected in the circumferential direction, and the first core block is formed with through holes penetrating through its opposite ends, and the through holes are filled with a filler containing combustible poison nuclides.

2. The water-cooled reactor fuel rod according to claim 1, characterized in that: The filler containing combustible poison nuclides is loose and porous pyrolytic carbon and 10 B. 157 Gd or 167 A mixture of Er oxides, or a loose porous pyrolytic carbon and 10 B. 157 Gd or 167 A mixture of Er carbides, or at least one of loose porous boron carbide, gadolinium carbide and zirconium boride.

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

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

4.

5. The water-cooled reactor fuel rod according to claim 1, characterized in that: The first pellet is made of uranium oxide, nitride and / or carbide; the enrichment of the first pellet is 2% to 10%.

6. The water-cooled reactor fuel rod according to claim 1, characterized in that: The fuel pellets further include at least one solid second pellet; The second core block is stacked on at least one side of the first core block in the cladding tube.

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

4.

8. The water-cooled reactor fuel rod according to claim 6, characterized in that: The second pellet is made of uranium oxide, nitride and / or carbide; the enrichment of the second pellet is 2% to 10%.

9. The water-cooled reactor fuel rod according to claim 6, characterized in that: The periphery of the end of the second core block is provided with an arc chamfer; and / or, a dish-shaped recess is provided in the middle of at least one end surface of the second core block.

10. The water-cooled reactor fuel rod according to claim 6, characterized in that: The fuel pellets include a plurality of the first pellets and at least two of the second pellets; A plurality of the first core blocks are stacked in sequence in the middle of the cladding tube, and at least two of the core blocks are respectively arranged between the first core block and the upper end plug and between the first core block and the lower end plug.

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

12. The water-cooled reactor fuel rod according to any one of claims 1 to 10, characterized in that: The cladding tube is filled with helium at a pressure of 0.1 MPa to 6 MPa.

13. The water-cooled reactor fuel rod according to any one of claims 1 to 10, characterized in that: The lower end plug is integrally formed with the cladding tube.

14. The water-cooled reactor fuel rod according to any one of claims 1 to 10, characterized in that: The water-cooled reactor fuel rod further comprises a cavity spring, which is arranged in the cladding tube and abuts between the upper end plug and the fuel pellet.

15. The water-cooled reactor fuel rod according to any one of claims 1 to 10, characterized in that: The length of the water-cooled reactor fuel rod is 1000 mm to 5000 mm.

Images