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.

I claim as my invention: 
     
       1. A fuel assembly for a nuclear reactor comprising: a bundle of fuel rods;   an upper tie plate assembly arranged at the upper end of said bundle, said tie plate assembly comprising:   an upper tie plate having holes to receive tie rods forming part of said bundle and openings for the flow therethrough of cooling water;   a plurality of lower side members mounted on and bounding said tie plate;   a plurality of spring seats mounted on said lower side members, one spring seat being located at each corner of said tie plate;   a plurality of upper side members mounted on said spring seats, one upper side member being mounted at each side of said tie plate and spaced above said lower side members;   a plurality of leaf springs mounted above said lower side members and below said upper side members, said leaf springs having their ends located within said spring seats and being formed of a plurality of superposed leaves, said springs being bowed upwardly at their midpoints when in an unstressed condition;   a plurality of sliders supported by said upper side members, one of said sliders engaging the upper surface of each of said springs adjacent its midpoint, and each of said sliders being adapted to engage a fixed portion of said reactor, whereby on expansion of said assembly, said sliders bend springs through positions in which they are substantially flat to positions in which they are downwardly bowed;   said leaf springs being mounted within said spring seats in such a manner that the ends of said springs are free to accommodate extension of said springs as the midpoints of aid springs are depressed by said sliders.