Review of WWER fuel behaviour compared with PWR fuel in IFA-503

The main objective of IFA-503 is to compare the behaviour of WWER fuel with PWR fuel. The test commenced in 1995 and concentrated on old generation WWER-440 fuel. The in pile data revealed insignificant differences in behaviour of the two types of fuel with the exception of larger densification of WWER fuel. The test was finished in November 1998 and, recently one of the rods has been sent to Kjeller for PIE to confirm the in-pile data on burnup, fuel dimensional and rod pressure changes. Preliminary PIE results compared with the in-pile data observed in IFA-503.1 are presented. Since March 1999 modified WWER fuels have been irradiated in IFA-503.2 to study thermal and mechanical behaviour compared with PWR reference fuel. 10 rods, with three types of WWER UO2 fuel pellets produced by MSZ Electrostal (Russia) and 2 reference rods with PWR specification pellets produced by IFE (Kjeller), are instrumented similarly to the first loading. The in-pile data have indicated that all types of the modified WWER fuels exhibit improved densification properties compared to the old generation WWER fuel tested in IFA-503.1. One of these fuels has shown thermal and mechanical performance similar to PWR reference fuel. The rod average burnup achieved at heat rates 20-25 kW/m is around 30 MWd/kg UO2 . A review of the in-pile measurements is presented. (Author)