WASH-1400

WASH-1400, 'The Reactor Safety Study', was a report produced in 1975 for the Nuclear Regulatory Commission by a committee of specialists under Professor Norman Rasmussen. It "generated a storm of criticism in the years following its release". In the years immediately after its release, WASH-1400 was followed by a number of reports that either peer reviewed its methodology or offered their own judgments about probabilities and consequences of various events at commercial reactors. In at least a few instances, some offered critiques of the study's assumptions, methodology, calculations, peer review procedures, and objectivity. A succession of reports, including NUREG-1150, the State-of-the-Art Reactor Consequence Analyses and others, have carried-on the tradition of PRA and its application to commercial power plants.

The report correctly foresaw the impact a tsunami could have on a nuclear power station. It concluded that "Some plants are located on the sea shore where the possibility of tsunami, and waves and high water levels due to hurricanes exist. The plant design in these cases must accommodate the largest waves and water levels that can be expected. Such events were assessed to represent negligible risks." (Section 5.4.6 "Other external causes")

WASH-1400 considered the course of events that might arise during a serious accident at a (then) large modern Light water reactor. It estimated the radiological consequences of these events, and the probability of their occurrence, using a fault tree/event tree approach. This technique is called Probabilistic Risk Assessment (PRA). The report concluded that the risks to the individual posed by nuclear power stations were acceptably small, compared with other tolerable risks. Specifically, the report concluded, using the methods and resources and knowledge available at the time, that the probability of a complete core meltdown is about 1 in 20,000 per reactor per year.

The study was peer-reviewed by the 'Lewis Committee' in 1977, which broadly endorsed the methodology as the best available, but cautioned that the risk figures were subject to large uncertainty.

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