Patent Number: 
Section: claims

1. A fuel rod for light water reactors, comprising:a cylindrical cladding tube formed of a ceramic base material primarily containing SiC, Al2O3, ZrO2, or Al6O13Si2;a connection formed of the same material as the cladding tube; andan end plug having a concave portion of a continuously curved surface shape adapted to house the connection,wherein the end plug is formed of the same material as the cladding tube,wherein a slanted surface formed at an end portion of the cladding tube, and a slanted surface formed at an end portion of the end plug are joined in contact with each other with a metallic joint material at a joint, andwherein the joint is supported by the connection. 2. The fuel rod for light water reactors according to claim 1,wherein the connection includes a columnar portion, and a curved surface portion that is provided at one end or both ends of the lengthwise direction of the columnar portion, and that is approximated to a portion of a spherical surface, andwherein the columnar portion and the curved surface portion have outer surfaces that are continuous to each other. 3. The fuel rod for light water reactors according to claim 2,wherein the concave portion of a curved surface shape of the end plug has a cylindrical portion opposite the columnar portion of the connection with a predetermined gap in between, and a depression approximated to a portion of a spherical surface, andwherein the cylindrical portion and the depression have inner surfaces that are continuous to each other. 4. The fuel rod for light water reactors according to claim 3, wherein the slanted surface formed at the end portion of the end plug has a shape that makes the inner diameter of the concave portion of a curved surface shape larger toward the cladding tube. 5. The fuel rod for light water reactors according to claim 4, wherein the slanted surface formed at the end portion of the cladding tube is slanted toward the end plug from the outer periphery side to the inner periphery side of the cladding tube so as to contact the slanted surface formed at the end portion of the end plug. 6. The fuel rod for light water reactors according to claim 5, wherein the metallic joint material joins at least the slanted surface of the cladding tube and the slanted surface of the end plug to each other, and the inner periphery surface of the cladding tube and the outer periphery surface of the connection to each another. 7. The fuel rod for light water reactors according to claim 6, wherein the metallic joint material has an average coefficient of thermal expansion of less than 10 ppm/K, and is one selected from silicon, a silicon alloy, titanium, a titanium alloy, zirconium, and a zirconium alloy when the ceramic material is a silicon carbide material, and wherein the metallic joint material is joined by brazing or diffusion joining. 8. The fuel rod for light water reactors according to claim 7,wherein the metallic joint material is deposited beforehand to the slanted surface of the cladding tube, and/or the slanted surface of the end plug, and to the inner periphery surface of the cladding tube, and/or the outer periphery surface of the columnar portion of the connection, andwherein the joint portions with the deposited metallic joint material are butted against each other, and locally heated with a laser, or a high-frequency or local heater. 9. The fuel rod for light water reactors according to claim 8, wherein the slanted surface of the cladding tube has a slope angle of 30° or more and 80° or less on its plane with respect to the axial direction of the cladding tube. 10. A fuel assembly that comprises a plurality of fuel rods bundled with a spacer, and that is loadable into a reactor core of a nuclear reactor,wherein the fuel rods include:a cylindrical cladding tube formed of a ceramic base material primarily containing SiC, Al2O3, ZrO2, or Al6O13Si2;a connection formed of the same material as the cladding tube; andan end plug having a concave portion of a continuously curved surface shape adapted to house the connection,the end plug being formed of the same material as the cladding tube,a slanted surface formed at an end portion of the cladding tube, and a slanted surface formed at an end portion of the end plug being joined in contact with each other with a metallic joint material at a joint, andthe joint being supported by the connection. 11. The fuel assembly according to claim 10,wherein the connection includes a columnar portion, and a curved surface portion that is provided at one end or both ends of the lengthwise direction of the columnar portion, and that is approximated to a portion of a spherical surface, andwherein the columnar portion and the curved surface portion have outer surfaces that are continuous to each other. 12. The fuel assembly according to claim 11,wherein the concave portion of a curved surface shape of the end plug has a cylindrical portion opposite the columnar portion of the connection with a predetermined gap in between, and a depression approximated to a portion of a spherical surface, andwherein the cylindrical portion and the depression have inner surfaces that are continuous to each other. 13. The fuel assembly according to claim 12, wherein the slanted surface formed at the end portion of the end plug has a shape that makes the inner diameter of the concave portion of a curved surface shape larger toward the cladding tube. 14. The fuel assembly according to claim 13, wherein the slanted surface formed at the end portion of the cladding tube is slanted toward the end plug from the outer periphery side to the inner periphery side of the cladding tube so as to contact the slanted surface formed at the end portion of the end plug. 15. The fuel assembly according to claim 14, wherein the metallic joint material joins at least the slanted surface of the cladding tube and the slanted surface of the end plug to each other, and the inner periphery surface of the cladding tube and the outer periphery surface of the connection to each another. 16. The fuel assembly according to claim 15, wherein the metallic joint material has an average coefficient of thermal expansion of less than 10 ppm/K, and is one selected from silicon, a silicon alloy, titanium, a titanium alloy, zirconium, and a zirconium alloy when the ceramic material is a silicon carbide material, and wherein the metallic joint material is joined by brazing or diffusion joining. 17. The fuel assembly according to claim 16,wherein the metallic joint material is deposited beforehand to the slanted surface of the cladding tube, and/or the slanted surface of the end plug, and to the inner periphery surface of the cladding tube, and/or the outer periphery surface of the columnar portion of the connection, andwherein the joint portions with the deposited metallic joint material are butted against each other, and locally heated with a laser, or a high-frequency or local heater. 18. The fuel assembly according to claim 17, wherein the slanted surface of the cladding tube has a slope angle of 30° or more and 80° or less on its plane with respect to the axial direction of the cladding tube.