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

A project on thermochemical data and modelling of ex-vessel cerium behaviou r has been conducted as part of the European Commission Fourth Framework Pr ogramme on Nuclear Safety. The objective of the study was to provide critic ally assessed thermochemical data and develop calculational methods for use in assessment studies of the consequences of melt-basemat interactions. Th e work programme comprised the critical assessment and experimental determi nation of thermochemical data for species of key importance to melt interac tions. A database has also been developed to model the multi-component syst em and calculations performed to predict the melt composition, Experimental determinations for silica and zirconia-based systems, for example measurem ents 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 predictio ns of the effects of ex-vessel interactions to factors such as accident con ditions (e.g., temperature, concrete type) and, uncertainties in the thermo chemical and kinetic data has also been assessed. (C) 2001 AEA Technology. Published by Elsevier Science B.V. All rights reserved.