Failure and its mechanism of LWR and research reactor fuels

Yanagisawa, Kazuaki

A LWR fuel consisted of UO pellet with zircaloy cladding and a research reactor fuel consisted of aluminide or silicide fuel cores with Al alloy. (1) LWR fuels were irradiated at the HBWR up to burn-up of 20 MWd/kgU and power ramped to have the PCI failure. The failure threshold of LWR was lower than that of HBWR. The in-core data was useful for obtaining the input data for the computer code FEMAXI. (2) Fresh or pre-irradiated LWR fuels were pulse-irradiated at the NSRR. For the fresh fuel, a failure occurred at 260 cal/g with cladding melt-brittle mechanism. For the pre-irradiated PWR fuel, a cladding split along one generatrix occurred at 118 cal/g. The failure mechanism may be the strong PCMI combined with the transient FGR. (3) Research reactor fuels failed by the through-plate cracking (les than 640 C) or cladding melt (above 640 C). A failure mechanism for the former was a tensile stress caused by a local uneven temperature profile during a quench.