EXPERIENCE WITH FAILED LMR OXIDE FUEL-ELEMENT PERFORMANCE IN EUROPEAN FAST-REACTORS

The performance of failed fuel has great significance for the safe and economic operation of LMR's, and considerable experience has accrued from experimental defect pin irradiations and naturally occurring failures in European test and prototype reactors. To data 60 natural fuel element failures have been recorded in PFR, Phenix and KNK II, 41 with exposed fuel and 19 as gas leakers. The various failures occurred during all stages of pin lifetimes, i.e. at the very beginning (0.3 at% burn-up) as well as at medium and at very high burn-up. The present experience extends up to 190 GWd/t and up to 135 dpaNRT. Based on the experience we can state: (i) Even large defects at end-of-life pins resulted in limited fuel loss. (ii) No pin-to-pin failure propagation has been observed. (iii) The reaction produces formed by the chemical reaction sodium/mixed oxide and the kinetics act beneficially and may protect open cracks. For the European Fast Reactor (EFR) project additional work is being performed, with regard to the EFR requirements of pin design (covering normal operation and incidental events) and the behaviour of failed pins under storage conditions.