Effect of initial coolant temperature on mechanical fuel failure under reactivity-initiated accident conditions

Sugiyama, Tomoyuki ; Umeda, Miki ; Sasajima, Hideo ; Suzuki, Motoe; Fuketa, Toyoshi

Pulse irradiation tests, simulating reactivity-initiated accidents (RIAs), were performed on high burnup fuels at high temperature (HT) in the Nuclear Safety Research Reactor (NSRR). The NSRR tests have provided data of fuel failure limit against the pellet-cladding mechanical interaction (PCMI) at RIAs, but the coolant temperature in the previous tests was limited to room temperature (RT) of around 20 C. Therefore, the obtained failure limits could be very conservative for RIAs at hot zero power or at operation. The possible effect of initial coolant temperature on the PCMI failure limit was investigated using a newly developed test capsule which can achieve 290 C. PWR and BWR fuel rods were tested both at RT and HT conditions. Comparison of the test results indicated that the increased cladding ductility at HT raised the failure limit. Hence, the PCMI failure criterion based on the NSRR RT data has more than adequate safety margin for RIAs at HT condition.