Operation method of connection part between container body and cover

A preparation method for performing an arbitrary operation with respect to a connection part between a container body of a nuclear reactor vessel and a cover after exposure of the connection part of the container body in a method where the connection part is exposed, the preparation method comprising the steps of:

• detaching said cover from said container body within water filling a cavity;
• arranging a fuel rod housing having an aperture at an upper portion, within the water;
• transferring fuel rods housed within the container body to the fuel rod housing via the aperture thereof;
• closing the aperture of the fuel rod housing while maintaining water-tightness;
• and
• draining water from the cavity so as to expose the connection part of the container body, wherein
• the arbitrary operation with respect to the connection part is performed thereafter.