KWU fuel performance with emphasis on high burnup

Over the past decade, KWU has carried out a large number of post irradiation examinations of standard and advanced test assemblies. Data from these programs, which extend over a wide range of linear heat generation rates and burnups of up to 46 GWd/t(U) (peak pellet), form the basis of fuel performance analyses and verification of design codes. Important aspects of fuel performance relevant with respect to further increased burnup are discussed. In particular, the fractional fission gases release, depending strongly on the linear heat generation rate but only moderately on burnup, is influenced by the fuel pellet microstructure. From a mechanistic point of view, the PCI failure threshold should not be seriously reduced at extended burnups. A factor in extended burnup, fuel rod external corrosion, shows a certain scatter which makes a reliable extrapolation still difficult. Altogether, it is concluded that an extended burnup target in the range of 55 GWd/t(U) is feasible with only minor design modifications