Abstract: A high temperature reactor having a reactor core filled with spherical fuel elements is provided comprising a graphite side reflector including at least one nose-like projection protruding radially into the reactor core from said graphite said reflector, said at least one nose-like projection including a vertically disposed cavity adapted to receive discrete absorber material elements introduced into said reactor core as well as a vertically disposed continuous opening which permits communication between said cavity and the core of the reactor, and sealing means positioned in said continuous opening and cooperatively engaged with the portion of said nose-like projections defining said vertically disposed continuous opening, said sealing means being so configured and so cooperatively engaged so as to permit gaseous communication between said cavity and said core while preventing passage of said discrete absorber material elements through said continuous passage.

Abstract: A nuclear-reactor assembly comprising a pressure vessel for the nuclear reactor and auxiliary vessels disposed in annularly spaced relationship around the reactor pressure vessel and communicating therewith by horizontal passages in the walls between the vessels. According to the invention, the outer surface of the reactor pressure vessel, which is otherwise generally cylindrical, is formed with vertical surfaces in the region of the passages against which complementary vertical planar surfaces of the auxiliary vessels lie. The spaces between the auxiliary vessels are filled in the plane of these passages by support blocks so that the blocks together with the auxiliary vessels form a compound disk which is prestressed inwardly by a peripheral prestressing element passing around the perimeter of the disk.