Patent Number: 
Section: claims

1. A maintenance/repair device for a reactor internal structure formed of a control-rod drive mechanism housing having a through-hole, for maintaining/repairing a reactor internal structure installed on a bottom of a reactor pressure vessel, the maintenance/repair device for reactor internal structure comprising:a device body configured to be fixed on the reactor internal structure; anda welding-part repair mechanism connected to the device body, the welding-part repair mechanism being configured to repair a welding part of the reactor internal structure,wherein a welding part of the reactor internal structure is repaired by the welding-part repair mechanism, while the device body is fixed on the reactor internal structure,the device body comprising:a frame to which the welding-part repair mechanism is connected;a guide connected to the frame and configured to be fitted to the through-hole in the control-rod drive mechanism housing for insertion into the through-hole; anda clamp mechanism disposed in the guide and configured to fix the device body on the control-rod drive mechanism housing, andwherein the clamp mechanism includes pads projecting outward of the guide so as to be pressed onto an inner surface of the control-rod drive mechanism housing when the device body is fixed on the control-rod drive mechanism housing. 2. The maintenance/repair device for reactor internal structure according to claim 1, wherein:the reactor internal structure is formed of an in-core instrumentation cylinder; andthe device body has: a frame to which the welding-part repair mechanism is connected; a guide connected to the frame, the guide being configured to be fitted to the in-core instrumentation cylinder; and a grip mechanism disposed in the guide, the grip mechanism being configured to fix the device body on the in-core instrumentation cylinder. 3. The maintenance/repair device for reactor internal structure according to claim 1, whereinthe device body has an elevation mechanism connected to the welding-part repair mechanism, the elevation mechanism being capable of moving in an up and down direction with respect to the frame. 4. The maintenance/repair device for reactor internal structure according to claim 3, whereinan outer circumference of the frame of the device body and an outer circumference of the control-rod drive mechanism housing have substantially the same diameters, whereby the welding-part repair mechanism can be continuously moved, along the outer circumference of the frame and the outer circumference of the control-rod drive mechanism housing, with respect to the device body in the up and down direction, by the elevation mechanism. 5. The maintenance/repair device for reactor internal structure according to claim 1, whereinthe welding-part repair mechanism has: a laser transmitter configured to send a pulse laser beam; an irradiation lens attachment body connected to the laser transmitter through a light guide cylinder and an irradiation head; and an irradiation lens disposed in the irradiation lens attachment body, the irradiation lens being configured to irradiate a pulse laser beam from the laser transmitter onto a welding part of the reactor internal structure so as to eliminate a residual stress of the welding part. 6. The maintenance/repair device for reactor internal structure according to claim 5, whereinthe irradiation lens attachment body is provided with an underwater camera for confirming a position and a direction of the irradiation lens. 7. The maintenance/repair device for reactor internal structure according to claim 5, whereinthe irradiation lens attachment body is provided with an apparatus configured to detect an ultrasonic wave that is generated from the welding part, when a pulse laser beam is irradiated from the irradiation lens onto the welding part.