Pressure vessel closure member

Claim 1

A REMOVABLE BUILT-UP METAL CLOSURE MEMBER HAVING A MULTIPLICITY OF SPACED ACCESS OPENINGS THERETHROUGH SUITABLE FOR A LARGE DIAMETER VERTICALLY POSITIONED PRESSURE VESSEL EMPLOYED AS A NUCLEAR REACTOR COMPRISING TWO HORIZONTALLY DISPOSED SPACED FLAT PARALLEL PLATES EACH COMPRISING A SINGLE MONOLITHIC SLAB OF METAL, CIRCULAR IN SHAPE, AND HAVING A DIAMETER GREATER THAN THE INTERIOR DIAMETER OF SAID PRESSURE VESSEL, COUPLING MEANS RIGIDLY UNITING THE PLATES ADJACENT THEIR PEIPHERIES AT LEAST AT SPACED POINT ALONG THOSE PERIPHERIES, VERTICALLY ARRANGED METAL SPACING PIECES EACH EXTENDING BETWEEN THE PLATES IN THE SPACE THEREBETWEEN INWARDLY FROM THE COUPLING MEANS AND WELDED AT THEIR UPPER AND LOWER ENDS TO SAID PLATES, SAID METAL SPACING PIECES HAVING ANGULARLY DISPOSED LIMBS AND BEING ARRANGED TO DIVIDE THE SPACE BETWEEN SAID PLATES INTO A MULTIPLICITY OF VERTICALLY EXTENDING CELLS EACH HAVING A SUBSTANTIALLY UNIFORM CROSS SECTION THROUGHOUT ITS HEIGHT AND BEING DEFINED ON ITS SIDES BY SAID LIMBS OF THE METAL SPACING PIECES AND TOP AND BOTTOM BY SAID PLATES, MANY OF THE CELLS BEING REMOTE FROM THE PERIPHERY OF THE CLOSURE MEMBER AND BEING SURROUNDED BY OTHER CELLS, ALIGNED ACCESS OPENINGS IN SAID PLATES PROVIDING AN UPPER AND A LOWER OPENING TO EACH OF SAID CELLS, VERTICALLY DISPOSED TUBE ASSEMBLIES SEALINGLY FITTED IN FLUID-TIGHT RELATIONSHIP INTO SAID ALIGNED ACCESS OPENINGS AND FORMING A PASSAGEWAY THROUGH SAID CELLS OPENING INTO SAID PRESSURE VESSEL, PLUG MEANS FOR SEALING THE UPPER ENDS OF SAID TUBE ASSEMBLIES, AND APERTURES IN SAID METAL SPACING PIECES FOR THE CIRCULATION OF A COOLING FLUID SERIALLY THROUGH SAID CELLS.