Device to allow for expansion of nuclear fuel assemblies

Abstract

An upper tie plate assembly for a nuclear reactor includes the usual tie plate having holes to receive the tie rod of the fuel assembly. A lower side member is welded to each side of the tie plate and there is a spring seat at each corner, connected to the lower side members. An upper side member parallels each lower side member at a higher elevation. At an intermediate elevation, there are leaf springs paralleling the side members, with their ends received within spring seats provided at the corners of the plate. Sliders are mounted on the upper side members and engage the midpoints of the upper surfaces of the springs. As the fuel assembly expands, the sliders, which engage an upper core plate of the reactor, deflect the springs from their normal, upperwardly bowed position, through a flattened position, to a downwardly bowed position. The ends of the springs are mounted within the spring seats in such a manner that they are free to accommodate extension of the springs. This avoids undesirable stresses in the springs. This arrangement leaves the central part of the tie plate free of obstructions to the flow of cooling water, and the spacing of the upper and lower side members and the springs leave room for the insertion of grappling members from either the inside or the outside of the tie plate assembly to lift the fuel assembly.