Thermochemical data and modelling for ex-vessel corium behaviour during a severe accident

A project on thermochemical data and modelling of ex-vessel corium behaviour has been conducted as part of the European Commission Fourth Framework Programme on Nuclear Safety. The objective of the study was to provide critically assessed thermochemical data and develop calculational methods for use in assessment studies of the consequences of melt–basemat interactions. The work programme comprised the critical assessment and experimental determination of thermochemical data for species of key importance to melt interactions. A database has also been developed to model the multi-component system and calculations performed to predict the melt composition. Experimental determinations for silica and zirconia-based systems, for example measurements of the chemical activities of Ce and La in melts, have been performed to assist in the validation of the models. The sensitivity in the predictions of the effects of ex-vessel interactions to factors such as accident conditions (e.g., temperature, concrete type) and, uncertainties in the thermochemical and kinetic data has also been assessed.