Behavior of high burn-up fuel cladding under LOCA conditions

Nagase, Fumihisa ; Chuto, Toshinori; Fuketa, Toyoshi

LOCA-simulated experiments were performed with the MDA, ZIRLO, M5, NDA and Zircaloy-2 cladding specimens sampled from high burnup fuel rods which were irradiated to 66-76 MWd/kg (local). Short test rods fabricated with the cladding specimens and dummy pellets were heated, isothermally oxidized at 1459 to 1480 K in steam flow, and finally quenched in flooding water. Neither split-fracture nor fragmentation occurred during the quench for the cladding specimens, oxidized to about 18-27% of the metallic thickness. Accordingly, the fracture boundary, a most important safety issue, is not reduced significantly by the high burn-up and use of the new alloys in the examined scope, though it may be somewhat reduced with pre-hydriding during the reactor operation as observed in unirradiated specimens.