Patent Number: 
Section: claims

1. A water jet peening (WJP) method for a nuclear reactor vessel comprising:disposing a clamping cylinder at the outer peripheral side of an instrumentation nozzle with a predetermined gap therebetween;fixing a positioning member provided in the clamping cylinder to the instrumentation nozzle at a position adjacent to the upper end of the instrumentation nozzle;moving an inner surface WJP nozzle downward to the instrumentation nozzle through the clamping cylinder;jetting high-pressure water to an inner surface of the instrumentation nozzle by moving the inner surface WJP nozzle downward in a rotation state while the high-pressure water including cavitation air bubbles is jetted from the inner surface WJP nozzle; anddischarging the high-pressure water jetted from the inner surface WJP nozzle to an outside of the instrumentation nozzle through a drainage hole provided in the positioning member. 2. The water jet peening method according to claim 1,wherein the high-pressure water is jetted from the inner surface WJP nozzle while a thimble tube drawn to an outside of the reactor vessel from the instrumentation nozzle through a conduit tube is not movable. 3. The water jet peening method according to claim 2,wherein a fixed state of the thimble tube and the conduit tube is monitored when the high-pressure water is jetted from the inner surface WJP nozzle to the inner surface of the instrumentation nozzle.