Principal issues and EPRI research work on core debris/concrete interactions

The ex-vessel progression of a postulated core melt-down accident leads to molten corium concrete interactions (MCCI), during which the gases generated from concrete decomposition react with the corium melt. Fission product and reactant-material release and aerosol formation occur due to vaporization-condensation processes. The timing, the magnitude and the chemical and physical form of the products of MCCI are extremely important in determining the overall source term resulting from postulated severe accidents. Recent risk estimates of certain BWR accident scenarios have indicated that the source term emanating from MCCI dominates the calculated risks. The physics and chemistry of the MCCI is very complex and not well understood. In this paper, they highlight the principal technical issues, which they believe need clarification and resolution through experimentation and validated analyses