PRESSURIZED FUEL ELEMENTS FOR NUCLEAR REACTORS

1374944 Fuel elements WESTINGHOUSE ELECTRIC CORP 22 Jan 1973 [16 Feb 1972] 3153/73 Heading G6C A fuel element comprises a sealed casing 26, e.g. of Zr alloy, which contains between the upper end plug 18 and the fuel pellets 24 a pressurized gas-filled plenum 12. A collapsible capsule 14, e.g. of stainless steel, which is disposed within the plenum 12, being suspended from the end plug 18 within a retaining spring 20, is designed to gradually collapse upon an increase in pressure within the plenum 12 above a predetermined value in order to maintain the plenum pressure substantially constant. An initially collapsed portion is provided at one end of the capsule 14 in the form of a dimple 16 machined in the capsule wall. When the internal pressure exceeds the predetermined value, collapse beyond that provided by the dimple 16 occurs and a slight reduction in internal pressure results. As more fission gas is generated the pressure will increase and the capsule will gradually collapse at what may be termed running collapse pressure. The internal pressure will then be maintained at a substantially constant level because as more fission gas is released, the collapse will propagate along the length of the capsule (Figs. 2, 3 and 4, not shown) at a rate sufficient to maintain substantially constant internal pressure.