Estimated TMI-2 vessel thermal response based on the lower plenum debris configuration

The TMI-2 accident resulted in extensive reactor core damage and release of fission products from the fuel. Recent defueling work has confirmed that 30 to 40% (40 to 55 metric tons) of the orginial core material achieved melting temperatures, and an estimated 15 metric tons of molten core material relocated to the lower head region of the reactor vessel. Because of the extensive core damage and core material relocation, the TMI-2 accident provides a unique opportunity to extend our understanding of the physical processes controlling the latter stages of in-vessel core damage progression. The TMI-2 data have provided important insight into the initial core heatup and relocation mechanisms, interaction of the molten core materials with the core support structures and vessel coolant, and the potential localized damage to the instrument assemblies and vessel head. This paper presents the results of recent analytical work to evaluate the long-term thermal response of the lower head.