Development and applications of the interim direct heating model for the CONTAIN computer code

A model for Direct Containment Heating has been developed for the CONTAIN code which takes account of the competing processes of melt ejection, steam blowdown, heat transfer among debris, gas and walls, chemical reactions in the debris droplets, intercell gas and debris transport, and de-entrainment of the suspended debris. Calculations of accident sequences with the model have shown that a qualitatively different understanding of the Direct Heating phenomenon emerges when more detailed multi-cell calculations are preformed within a system-level containment code, compared to the relatively simplistic single cell, adiabatic calculations which have been used in the past. Results are presented for the TMLB' sequence at the Surry and Sequoyah plants, and a sensitivity study for some of the most important uncertain parameters is described.