Nuclear reactors

A nuclear fuel element assembly is described that is suitable for gas-cooled reactors operating with a fast neutron spectrum, although it is equally applicable to thermal reactors. It consists of an open ended elongated tubular wrapper of heat transfer material, with a coolant inlet at one end and a coolant outlet at the other end. One or more clusters of fuel pins are supported within the wrapper, with axes parallel to one another and to the wrapper axis, and in spaced apart relationship. The tubular wrappers each contain a loose bed of fission product retaining fuel particles. Each of the tubular wrappers has apertures for the passage of coolant, so that when the wrapper is placed in the coolant flow path the fuel is cooled by coolant passing between the wrappers and through the coolant permeable fuel. A cluster of wrappers containing coolant permeable fissile fuel may be mounted between clusters of fertile material enclosed in fuel cans. The coolant permeable fuel may incorporate baffles of coolant impermeable material to influence the flow direction of coolant through the fuel. (U.K.)