Behavior of high burnup fuels under RIA and LOCA conditions

Nakamura, Takehiko ; Fuketa, Toyoshi; Nagase, Fumihisa ; Sugiyama, Tomoyuki 

The paper describes and discusses results from an experimental program performed at Japan Atomic Energy Agency (JAEA) for high burnup fuel behavior during a reactivity-initiated accident (RIA) and a loss-of-coolant accident (LOCA). The program is comprised of RIA-simulating experiments in the Nuclear Safety Research Reactor (NSRR), LOCA-simulating tests in Reactor Fuel Examination Facility (RFEF), and cladding mechanical tests. The results from recent NSRR experiments reflect the better performance of the new cladding materials in terms of corrosion, the thinner oxides and accordingly lower hydrogen content generated during irradiation in the PWR. It can be concluded that the improved corrosion resistance gives a larger safety margin against the PCMI (Pellet/Cladding Mechanical Interaction) failure. A recent LOCA test indicates that failure boundary is not reduced significantly by PWR irradiation in the examined burnup level. Hence, in the burnup level of the present study, differences were not significant between irradiated and unirradiated specimens in terms of threshold of fracture during quenching, although the fracture threshold is reduced as initial hydrogen concentration increases.