Release of Radioactivity from Large Containment Leaks During Severe Accidents

Introduction The goal of this work is the investigation of a severe accident with a large containment leak from the beginning of the accident. Normally the course of severe accidents and their associated phenomena are investigated with the assumption of an intact containment from the beginning of the accident. This intact containment has the ability to retain a large part of the radioactive inventory. In these cases there is only a release via a very small leakage due to the untightness of the containment up to cavity bottom melt through. Different possibilities of leakages from the containment as part of the safety analysis of the containment are described in volume two of the "Deutsche Risikostudie Kernkraftwerke". The range of the leakages from the beginning of the accident is covered by three different representative leakage sizes. The maximum leakage of the containment has a diameter of 300 mm. In addition the increasing relevance of terrorism suggests a closer look at this kind of severe accidents. This work supplements a series of studies investigating the behaviour of a VVER-1000-type reactor during severe accidents under different accident management strategies. The focus in this study is on the "Station Blackout" sequence (or TMLB in the WASH-1400 nomenclature). To be able to compare the results with earlier calculations for accidents with an intact containment, the calculations were performed using the Source Term Code Package (STCP), hydrogen explosions are not considered.