Domed diaphragm / insert plate for a pressure vessel access closure

A substantially rigid steam generator pressure vessel having a wall with an access opening of 2 in. (5.1 cm) or larger and a closure for the access opening comprising:

• a sealing surface on said wall surrounding the access opening;
• one of either a male or female locking device formed on or in said wall radially outward from said sealing surface at a plurality of locations around said access opening;
• an insert positioned to span said access opening, said insert having a peripheral flange that rests over at least a portion of said sealing surface and a continuously rounded concave portion completely extending between opposing sides of an inner edge of the flange and completely closing off the access opening with the rounded concave portion extending into the access opening;
• a sealing member between the sealing surface and the flange of the insert;
• a cover extending over the access opening and the insert and extending radially outward to at least said one of either the male or female locking device;
• and
• the other of the male or female locking device connecting the cover to the wall by engaging the one of the male or female locking device and pressuring the cover against the flange of the insert.