One of the terror scenarios for nuclear power plants is a severe damage of the reactor containment caused by a plane crash or a missile. Owing to the loss of electric power the cooling of the core would not be maintained, leading to a core melt accident. Normally in the course of severe accidents an intact containment has the ability to retain a large part of the radioactive inventory. The goal of this work is the investigation of the behaviour of the radioactive releases from a VVER-1000 reactor during a severe accident with a large containment leak from the beginning of the accident. The results are compared with the release in a severe accident via a very small leakage due to the looseness of the containment.