Visual In-Pile Fuel Disruption Experiments

Abstract

An area of considerable importance in reactor safety concerns the early time fuel behavior in a loss-of-flow (LOF) accident in fast reactor systems. Redistribution of core materials, dependent on the mode of fuel pin disruption, can have a dominant effect on the probability of a subsequent energetic excursion. In an LOF, occluded fission gases in the fuel may produce rapid clad and fuel dispersal following fuel heating. The net effect may be significant negative reactivity and a non-energetic accident termination. In the absence of dispersal, a recriticality may occur. Hypotheses of fuel disruption have included, among others, that the fuel could (1) break up into a ''dust-cloud'', and disperse rapidly; (2) swell in the solid state, without rapid dispersal; (3) form a liquid froth and disperse rapidly; or (4) melt and slump with release of fission gas. In order to determine which of these hypotheses, if any, are correct, in-pile experiments and corresponding analyses have been conducted at Sandia Laboratories. This paper presents the first results from these experiments.