Sealed stopper for an opening in a tubing for joining a chamber and a piping, particularly in the steam generator of a nuclear pressurised water reactor

A sealed stopper for plugging an opening of tubing connecting a chamber with piping, a fastening ring being arranged around the opening of the tubing leading into the chamber and secured onto an inner surface of the chamber, the stopper comprising:

• a rigid bearing plate formed by a cylindrical part and a flat annular part, the cylindrical part having a diameter smaller than an inner diameter of the fastening ring, and the flat annular part having a diameter larger than the inner diameter of the fastening ring, and
• a sealing member carried by the cylindrical part of the bearing plate, the sealing member including a seal having a planar flexible central part of narrow thickness extending underneath the cylindrical part of the bearing plate and a peripheral part, the peripheral part being radially deformable by a central expander for expanding the peripheral part against the inner surface of the fastening ring, the central part being integral with the peripheral part, the peripheral part being thicker and more resistant than the central part of the seal and delimits, with the central part, an inner housing for the central expander, the inner housing being open at an end thereof that is opposite the central part.