GB1292335A - Improvements in and relating to fuel elements for nuclear reactors - Google Patents

Abstract

1292335 Fuel elements NUCLEAR POWER GROUP Ltd 31 March 1970 [23 April 1969] 20753/69 Heading G6C A fuel element comprises a nuclear fuel member located in a graphite container, adjacent surfaces of both the container and the fuel member having fins, the fins on the container overlapping radially those on the fuel member. Initially the fuel member is a close fit inside the container so as to minimize gaps at the fuelgraphite interface. Differential shrinkage of fuel member and graphite during operation causes gaps to open up which can result in overheating of the fuel member. The radial height of the fins is such, however, that an overlap is maintained even after the gaps have opened up to the maximum degree. Various fin shapes are possible and in one embodiment the fins are of sawtooth form so designed as to induce relative rotation between the fuel member and the container. As a result of the overlapping fins heat can be transferred in a circumferential direction which means that the temperature drop across the fuel-graphite interface is less dependent on radial gap width than with elements without fins of the kind described. Any contact between the fins reduces the temperature difference between the fuel and graphite and hence reduces the risk of overheating of the fuel in local regions. Typically the fuel member is of enriched uranium in particulate form in a graphite matrix. The fuel member may be annular in crosssection and have both inner and outer graphite containers, each provided with fins overlapping radially corresponding fins on the fuel member. In this case, the coolant flows between the outer surface of the inner container and the inner surface of the fuel member, as well as over the outer surface of the outer container and the inner surface of the inner container.