On the prediction of the reactor vessel integrity under severe accident loadings (RPVSA)

In order to allow more reliable predictions on the lower head response unde r core melt-down conditions, the temperature distribution has been analysed including the natural convection in the corium pool. Furthermore, the mech anical models and the failure criteria have been improved based on the RUPT HER and FASTHER experiments where typical temperature gradients are simulat ed. Lower head local melting as well as corium crust development has been a ddressed in the CORVIS experiments studying the contact between an alumina/ iron thermite and a thick steel plate. The upper head loading by corium imp act due to a postulated in-vessel steam explosion has been investigated by the BERDA experiments. Similarity rules were considered such that the resul ts can be directly converted to reactor conditions. Based on these investig ations admissible steam explosion energy releases are determined which the upper head can carry. If these limits are not exceeded the reactor containm ent cannot be endangered by broken head fragments. To provide the necessary basic data, mechanical material tests have been performed. (C) 2001 Elsevi er Science B.V. All rights reserved.