Patent Number: 
Section: claims

1. A nozzle repair method for a nuclear reactor instrumentation nozzle comprising an in-core instrumentation cylinder inserted into an attachment hole in a semi-spherical portion of a nuclear reactor vessel and a groove-weld portion between an inner surface of the semi-spherical portion and an outer surface of the in-core instrumentation cylinder, the semi-spherical portion being provided with a buttered-welding layer having stress corrosion cracking resistance on an inner surface thereof, by using a plug including a plug body having a columnar shape, a vertical wall portion protruding upward from an upper surface of an peripheral portion of the plug body, a concave portion surrounded by the vertical wall portion, a protrusion protruding downward from a lower surface of the plug body, a flat lower surface formed around the protrusion on the lower surface of the plug body, a screw shaft extending downward from a bottom surface of the protrusion and having a screw portion at an end portion thereof, the nozzle repair method comprising:removing the in-core instrumentation cylinder from a reactor vessel by severing the groove weld portion between the groove weld portion and the in-core instrumentation cylinder;forming a plug attachment portion by forming a columnar opening at the inner surface of the semi-spherical portion such that an axis of the columnar opening aligns with an axis of the attachment hole;inserting the plug to the plug attachment portion;deforming the flat lower surface of the plug and a bottom surface of the plug attachment portion by applying a pressing load to the plug toward the semi-spherical portion by attaching a support plate and a nut to the screw portion of the screw shaft such that the support plate is positioned between the nut and an outer surface of the semi-spherical portion, and screwing the nut to the screw portion; andwelding the plug to the plug attachment portion with the flat lower surface of the plug and the bottom surface of the plug attachment portion deformed. 2. The nozzle repair method according to claim 1,wherein the welding includes welding an outer peripheral portion of the plug to the buttered-welding layer while the plug is fitted into the plug attachment portion. 3. The nozzle repair method according to claim 1,wherein the welding includes welding an outer surface of the vertical wall portion to the semi-spherical portion while the plug is fitted into the plug attachment portion.