The move is the third in a series of major steps to enhance the post-11 September security of nuclear power plants.

The NRC will seek comment from the public, the nuclear industry and the technical community on the proposal later this year.

In 1985 the NRC said it expected reactor designers to build in more safety features to cope with beyond design basis severe accidents as reactor designs advanced although it did not require specific features, leaving that to plant designers.

However, the proposed rule will affect new applicants for reactor design certification and applicants for a combined licence that does not reference a certified design.

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