Morphology change of rock-like oxide fuels in reactivity-initiated-accident simulation tests

Pulse irradiation tests under simulated reactivity-initiated accident (RIA) conditions were performed with three types of rock-like oxide (ROX) fuels. Single phase yttria stabilized zirconia (YSZ), homogeneous mixture of YSZ/spinel and YSZ particle dispersed in spinel type ROX fuels were pulse irradiated in the Nuclear Safety Research Reactor (NSRR). Mode and threshold of the fuel rod failure including its consequences were investigated under the RIA conditions. The cladding failure occurred in a burst type mode in all the three types of ROX fuel tests with considerable fuel melting. Even though the mode was quite different from those of UO2 fuel, failure threshold enthalpies of the ROX fuels were close to that of UO2 fuel at about 10 GJ m−3. The consequence of the failure of the ROX fuels rods was different from the one of UO2 fuel rods, because molten fuel dispersal occurred at lower enthalpies in the ROX fuel tests. Change of the fuel structure and material interaction in the transient heating conditions were examined through optical and secondary electron microscopy, and electron probe micro analysis.