On the application of probabilistic risk assessment to reactors with inherently safe features

In this paper, it is shown that because of the public perception of the risk of nuclear power and the likelihood that in the event of a severe core damage accident in a reactor claimed to have a high degree of inherent safety, it is necessary to reconsider the basis for establishing safety objectives. It is shown that, if there were a large program of inherently safe reactors, the safety objectives would be determined more by investment risk than by the public health risk. These considerations lead to an objective on the order of 1 × 10⁻⁷ per r.yr (reactor year) for the probabability of a severe core damage accident. It is also shown that the introduction of inherently safe features leads to a considerable change in the allocation of the safety goal between the major safety functions. For these reactors, a major portion of the allocation shifts from the decay heat removal function to the scram function, with emphasis on insuring the integrity of critical structures.