In-Pile Experiments on Meltdown of EBR-II Mark I Fuel Elements in Stagnant Sodium

Experiments have been performed in-pile, using the Transient Reactor Test Facility, to study the meltdown behavior under transient heating of metallic Experimental Breeder Reactor-II fuel elements contained in stagnant sodium. Threshold of failure, modes of failure, and post-experiment distribution of fuel were obtained for a range of experimental conditions including uniform axial power and axial-power profile shaped to approximate a typical power profile of a fast-reactor core. Samples were exposed both with sodium initially at saturation conditions, and with sodium pressurized to inhibit boiling. Although the presence of stagnant sodium was found to modify qualitatively the results found previously for dry EBR-II samples, the changes were not great, and results were consistent with those for dry elements.