Method for maintaining a nuclear reactor

A maintenance method for a nuclear reactor,

• the nuclear reactor comprising
• at least one drive assembly of a control rod assembly,
• each drive assembly comprising
• an adapter rigidly attached to a closure head of a pressure vessel of the nuclear reactor,
• a casing for receiving a mechanism for lifting a drive rod of the control rod assembly and
• a sheath for receiving the drive rod,
• the casing having a casing lower end connected in a leak-tight way to the adapter,
• the casing having a first lip at a casing upper end,
• the sheath having a second lip at a sheath lower end,
• the first lip and the second lip being welded together and forming an omega seal,
• the maintenance method comprising the following steps:
• removing the first and second lips;
• carrying out at least one maintenance operation on the control rod assembly;
• creating a welding surface at the casing upper end by machining the casing upper end;
• and
• creating a leak-tight welded connection between the casing and the sheath or a replacement sheath,
• by welding the welding surface and a matching welding surface provided
• at the sheath lower end of the sheath
• or at a sheath lower end of the replacement sheath.