The use of probabilistic methods in the licensing of nuclear power plants: A recent example

In 1981 the Swedish government decided that the nuclear power plant at Barsebaeck in southern Sweden should be provided with filtered ventilation. The main reason was to prevent severe ground contamination in case of an accident. A ventilating device was connected in late 1985. The Government also decided that no later than 1989 all other Swedish power plants should be provided with some kinds of devices assuring as good a protection for the population around these plants as around Barsebaeck. In handling this matter and the licencing questions connected to it our institute has partly relied upon probabilistic methods and considerations. In short, the following actions have been taken: The power plant owners have supplied our institute with results from systematic reliability studies (involving probabilistic arguments) and some preliminary suggestions for solutions. Combining these with results from probabilistic studies performed by ourselves and with a number of criteria for acceptance of risk (some of which probabilistic) we have formulated some conditions that must be fulfilled before licencing of the arrangements required. In the last stage of the process the plant owners are supposed to use as one tool probabilistic arguments to make sure that the conditions are fulfilled. The paper presents the working process in some details, with the emphasis put on the probabilistic approaches. (author)