Risk analyses of the Ringhals plants: Containment behaviour and filtered vent

Abstract

In 1981, the Swedish Government requested that the potential for the accidental release of radioactive materials from Swedish Nuclear Power Plants should be investigated, and that the need for filtered vents or other mitigative devices should be evaluated. For the SSPB Ringhals plant probabilistic safety analyses were made for the units No. 1 (ASEA-ATOM BWR) and No. 2 (Westinghouse PWR) and some additional analyses for units Nos. 3 and 4 (similar to No. 2). After review of the analysis results by the Swedish Nuclear Power Inspectorate the Swedish Government issued licensing requirements with respect to severe accidents, which include requests for containment venting systems and limits for permissible release during an accident. The analysis comprised estimates of the failure pressure and failure mode for each containment including investigations of possible leakage before gross rupture. The results demonstrate the importance of the containment with respect to preventing releases of radioactive material during severe accidents and of plant specific features when evaluating the containment behaviour and its influence on accident sequences. Work is presently going on to implement the strategy for handling severe accidents including new installations to protect the containment by pressure relief and controlled venting combined with means for providing back-up sources of water for the containment sprays.