Fuel pins and core response under LMFBR top accident conditions

Out-of-reactor experiments are currently being performed at Argonne National Laboratory to examine fuel sweepout and related post-failure phenomena under hypothetical TOP accident conditions. These tests are supplementing the TREAT MARK-II loop data base by keying on effects of important parameter variations such as system hydraulics and intrabundle coherency. In these tests, molten UO/sub 2/, generated by a thermite reaction at 3470/sup 0/K, is injected over approximately 40 msec into flowing sodium in a bundle of simulated LMFBR-type fuel pins. Hydraulic conditions in the bundle are selected to match conditions in either the MARK-II loop (HUMP-series) or the current design LMFBR subassembly (CAMEL-series). To date, four tests have been performed in both single-pin and seven-pin configurations representing coherent and incoherent subassembly power-to-flow cases, respectively. Details of the fuel motion were observed using a flash x-ray cine system. A compilation of significant findings from the four sweepout tests is presented.