Validation strategies for severe accident codes with special emphasis given to integral codes

The Concerted Action project VASA (Validation Strategy of Severe Accident Codes) is focused on the understanding of current approaches in different European countries to validate the codes developed or used by them and on reaching a consensus on the procedure to come to a common European validation strategy for severe accident codes. It is performed jointly by 15 partners. With special respect to the end-user partners in VASA the validation needs were discussed not only, from the phenomena to be necessarily taken into consideration, but also from their contribution to risk. The phenomenon-oriented approach and the risk-oriented one are complementary to each other in the way that the last one leads to a hierarchy for the validation of the great number of severe accident phenomena. On one hand risk orientation requires the modeling of technical systems in severe accident codes. On the other hand this leads to high demands on experiments used for validation. Among others such experiments should be in general related to severe accident measures and in detail applicable to plant specifies.