Method for Securing and Confining the Gasket Plane of a Vessel of a Nuclear Reactor and a Gasket for Applying this Method

A method for securing and confining a gasket plane of a vessel of a nuclear reactor during an operation for closing the vessel in order to prevent a migration of solid material particles towards an inside of the vessel, the gasket plane being formed by a ring-shaped recess on a flange of the vessel and by a ring shaped shoulder on a lid of the vessel, the ring shaped recess on the flange and the shoulder facing each other and each including a vertical wall delimiting between them a gap after laying the lid on the vessel flange, the shoulder including a horizontal wall provided with two O-ring seal gaskets wherein after having disassembled the lid and laying the lid on a support, the method comprises the following steps:

• placing around the shoulder of the lid a ring-shaped gasket formed by a metal strip maintained on the vertical wall of the shoulder by self-maintaining members firmly attached to the metal strip;
• placing the lid bearing the ring-shaped gasket above the vessel by positioning it at a determined height and performing a cleanliness inspection of the gasket plane;
• lowering and laying the lid on the vessel so that end side edges of the metal strip come into contact with a horizontal wall of the lid and of the vessel flange, respectively;
• attaching the lid on the vessel flange;
• and
• leaving the ring-shaped gasket in place during a whole operating cycle of the reactor.