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 between an inner surface of the semi-spherical portion and an outer surface of the in-core instrumentation cylinder, the method comprising steps of:disconnecting the in-core instrumentation cylinder from the nuclear reactor vessel by severing the groove-weld therebetween;removing the in-core instrumentation cylinder from the semi-spherical portion;forming a surface buttered-welding portion by buttered-welding a surface of the groove-weld;forming a welding groove by grooving the surface buttered-welding portion;inserting a new in-core instrumentation cylinder provided with an instrumentation equipment guide passage and a groove portion into the attachment hole, the instrumentation equipment guide passage penetrating the new in-core instrumentation cylinder in an axial direction thereof, the groove portion being provided radially outside of and along a circumference of the instrumentation equipment guide passage, one end of the groove portion being opened in the axial direction; andfixing the new in-core instrumentation cylinder by groove-welding the welding groove to an outer circumference of the new in-core instrumentation cylinder. 2. The nozzle repair method according to claim 1, wherein the step of forming the surface buttered-welding portion includes performing buttered-welding on an area extending from the surface of the groove-weld to the inner surface of the semi-spherical portion and to the attachment hole. 3. The nozzle repair method according to claim 1,wherein after the step of forming the surface buttered-welding portion on the surface of the groove-weld, an inner surface of the attachment hole is machined. 4. The nozzle repair method according to claim 1,wherein the welding groove is formed within an area of the groove-weld. 5. The nozzle repair method according to claim 1,wherein the new in-core instrumentation cylinder includesa main body portion which is inserted into the attachment hole and in contact with an inner surface thereof,a support portion which is continuous to the upper end of the main body portion and has a diameter smaller than the main body portion,the instrumentation equipment guide passage which penetrates the main body portion and the support portion, andthe groove portion of which the end is opened to a stepped portion between the main body portion and the support portion. 6. The nozzle repair method according to claim 1,wherein a welding material used to fix the new in-core instrumentation cylinder to the semi-spherical portion is a material having higher stress corrosion cracking resistance than the welding material of the groove-weld.