An Evaluation of the Failure of a PWR Lower Head During a Core Meltdown Accident

This paper presents an analysis of ablation of lower vessel head during a core meltdown accident. The analysis if limited to PWR systems with no penetration tubes attached to the lower vessel head. The case considered is characterized by the discharge of a corium jet at a relatively slow rate into the lower plenum. The assumption of the breakup of the jet stream results in the solidification of debris particles and the formation of a debris bed thermally attacking the lower head wall. Detailed analyses were performed to determine the debris/coolability and the ablation of the lower head wall. Parameters which have significant effect on the results were identified. Parametric studies were performed to reflect uncertainties associated with the various phenomenological processes occurring during corium relocation into the lower head.