Nuclear reactor facility

A nuclear power facility comprising a pressurized-water reactor pressure vessel, at least one vertical steam generator horizontally offset from said vessel, a main pressurized-water coolant pipe loop interconnecting said pressure vessel and a lower portion of said steam generator, said loop containing circulating pressurized-water coolant, a concrete structure forming a steam generator and loop and extending upwardly and horizontally surrounding said steam generator and at least a substantial portion of said loop to a height above said steam generator and having an open top above said steam generator, said concrete structure forming at least one operating room separated from said steam generator room by one of said walls extending upwardly, accidental release of said coolant from said loop forming vapor having a vapor pressure, a horizontal ceiling above said steam generator and closing said top so that said release causes said steam generator room to be pressurized under said vapor pressure, and a containment shell enclosing said structure including said rooms and forming a space of substantial area above said steam generator room, said ceiling being a metal ceiling formed by a metal grid-like construction defining a plurality of vertical openings and having horizontal sheet metal plates positioned on said construction and normally closing said openings, said plates being strong enough for personnel to walk upon but light enough in weight to be displaced upwardly to open said openings when the plates receive upward force from said vapor pressure in said steam generator room resulting from said loop accidentally permitting a release of said pressurized-water coolant, said opening when open being large enough in cross-sectional area collectively, to release said vapor pressure into said space to a degree substantially reducing said vapor pressure within said steam generator room and on said one of said walls extending upwardly and separating said equipment room from said steam generator room, and connecting means for connecting said plates to said metal grid-like construction and holding the plates against complete separation therefrom when forced upwardly by said fluid vapor pressure, said connecting means permitting said plates to swing upwardly when displaced to open said openings, said metal grid-like construction connecting with said open top of said concrete structure and being held thereby against horizontal displacement, and said generator having a top portion adjacently below said construction and means for connecting said top portion with said construction to restrain said top portion from horizontal displacement while permitting vertical movement of said top portion.