Behavior of YSZ based rock-like oxide fuels under simulated RIA conditions

Nakamura, Takehiko ; Kusagaya, Kazuyuki*; Sasajima, Hideo ; Yamashita, Toshiyuki; Uetsuka, Hiroshi

Pulse irradiation tests of three types of ROX fuel, i.e. YSZ single phase, finely mixed two phase composite of YSZ and spinel, and the other composite of larger YSZ particles dispersed in spinel matrix, were conducted in the NSRR to investigate their behavior under RIA conditions. Owing to their lower melting temperatures than that of UO fuel, melting of ROX fuel occurred while the cladding was still solid and intact in the accident conditions. Therefore, consequence of the ROX fuel failure was quite different from that of UO fuel. When the ROX fuels failed, a considerable amount of the molten fuel was released out to the surrounding coolant water. In spite of the release, no significant mechanical energy generation due to fuel/coolant thermal interaction was observed in the tested enthalpy range below 12 GJ/m. In terms of the failure threshold, on the other hand, the ROX fuels failed at fuel volumetric enthalpies above 10 GJ/m, which was comparable to that of UO fuel. The results highlighted controlling parameters on the fuel behavior under the RIA conditions.