Patent Number: 
Section: claims

1. A nozzle repairing method of repairing an instrumentation nozzle in which an in-core instrument tube is inserted into an attachment hole formed in a semi-spherical portion of a nuclear reactor vessel having a buttered welding layer on its inner surface and an inner surface side of the semi-spherical portion includes a first connection portion and a second connection portion formed in a groove-welding portion so as to fix the in-core instrument tube, the nozzle repairing method comprising:removing the first connection portion with respect to the in-core instrument tube in the groove-welding portion;removing the in-core instrument tube from the semi-spherical portion;disposing a tab plate inside an upper end portion of the attachment hole after removing the in-core instrument tube;forming a surface buttered welding portion to cover surfaces of at least a portion of the tab plate, the second connection portion and at least a portion of the buttered welding layer after disposing the tab plate;grooving a part of the second connection portion with respect to the semi-spherical portion in the groove-welding portion while leaving a remaining of the second connection portion after forming the surface buttered welding portion;inserting a new in-core instrument tube into the attachment hole; andgroove-welding the inner surface side of the semi-spherical portion so as to fix the new in-core instrument tube. 2. The nozzle repairing method according to claim 1,wherein the in-core instrument tube is removed from the semi-spherical portion, and buttered welding is performed on a surface of the groove-welding portion. 3. The nozzle repairing method according to claim 2,wherein when performing the buttered welding on the surface of the groove-welding portion, the buttered welding is performed so as to extend to the inner surface of the semi-spherical portion and the buttered welding is performed so as to extend to the attachment hole. 4. The nozzle repairing method according to claim 1,wherein the groove-welding includes using a material having stress corrosion resistance higher than that of a welding material of the groove-welding portion as a welding material used when fixing the new in-core instrument tube to the semi-spherical portion. 5. The nozzle repairing method according to claim 1,wherein an operation is performed in an air space as the periphery of at least the instrumentation nozzle. 6. The nozzle repairing method according to claim 5,wherein the flow of water is stopped at upper and lower ends of the existing in-core instrument tube, and the water inside the nuclear reactor vessel is drained so as to form the air space.