Whether a Theory of Nuclear Safety is deterministic or probabilistic? A metatheory

Theoretical criteria for design or regulatory safety of nuclear power plants often take the form of requirements that some model of the “capacity” of the plant to respond to a hypothesized threat sufficiently exceed a model of the “load” presumably placed upon the plant by that threat. Either of capacity or load can be deterministic or probabilistic, which leads to a four-type typology, as opposed to the traditional classification of theories of nuclear safety as either deterministic or probabilistic. Concrete examples of each of the four types are provided. Possible uses of this viewpoint for design and regulation are discussed, especially as regards melding of the basically deterministic notion of safety margins with its natural probabilistic counterpart of requiring load exceed capacity with only very small probability. Use of this viewpoint is illustrated by using it as a framework within which to describe the regulatory impact of the well-known ECCS hearings of the 1970s.