Summary and evaluation of transient test data on extended fuel motion resulting from unprotected loss of flow

Experimental data on fuel failure and its consequences are used to provide predictions of the extended fuel motion that would occur after a hypothetical core-disruptive loss-of-flow accident without scram in the Fast Test Reactor. These data indicate the existence of fuel-dispersal mechanisms, slow collapse of fresh fuel, resistance to collapse of irradiated fuel, the absence of accelerated collapse mechanisms (such as cladding-coolant vapor ''explosions''), and the fact that real LMFBR conditions inhibit rapid sodium-vaporization events. These data indicate that severely damaged subassemblies will not be coolable in situ by returning sodium after the accident, because of steel and fuel blockages, and suggest that the severely damaged, melted fuel will eventually disperse upward under the influence of vapor generated by decay heating