Fastening and loosening device for stud bolts and nuts of a reactor vessel

A fastening and loosening method for a fastening and loosening device having a plurality of stud bolts screwed into an object to be fastened and a plurality of nuts respectively screwed onto the stud bolts, the device configured to rotate a respective nut, causing tension to act on a respective stud bolt, in a shaft center direction, away from the object to be fastened, to perform fastening or loosening, the method comprising:

• providing a device main body having an upper portion movably supported along an arrangement direction of the stud bolts;
• providing a bolt tensioner supported by the device main body and being freely movable along the shaft center direction of the stud bolts;
• providing a guide device provided in a lower portion of the device main body and having right and left guide members contactable with an outer periphery of the nut from both right and left sides of a moving direction of the device main body;
• and providing a guide position adjustment device capable of moving at least one of the right and left guide members in a horizontal direction intersecting with the moving direction of the device main body.