Development in design and engineering of KWU fuel for light and heavy water reactors

On the basis of an excellent performance record which must be maintained, recent activities for the development of advanced fuel assemblies concentrate on improved neutron economy and fuel utilization, capability for increased discharge burnup and improved operational flexibility. Our experience covers fuel design and engineering activities for Pressurized Heavy Water Reactors (PHWR) as well as for Light Water Reactors (LWR) of the PWR and BWR type. Due to many similarities in design parameters, operating conditions and technological considerations, optimization in one area is frequently to the benefit of the others, too. Examples are the development of improved manufacturing techniques, the use of prepressurized fuel rods, slight enrichment of PHWR fuel and the implementation of Zircaloy spacer grids in PWRs. Means to improve fuel utilization include also advanced fuel management strategies combined with the use of burnable absorbers in PWRs and moderator redistribution in fuel assemblies for BWRs. Designs with low linear heat generation rate in LWRs (BWR 9x9 and PWR 18x18) improve the technological burnup potential and the operational flexibility due to increased margins to limiting technological and thermalhydraulic conditions