On the extent of emergency actions for the protection of the public after accidental activity releases from nuclear power plants

Results are reported for modelling the external radiation dose from the ground occurring after a nuclear accident which releases radioactive material into the atmosphere. The areas contaminated are classed into 4 areas depending on the extent of contamination and the appropriate action to be taken in each area is listed. Various weather conditions and methods of depositing the radioactivity from the atmosphere to the ground are included in the computer programs. Activity concentration and ground contamination are calculated at discrete mesh points, and the effects of using fine and coarse-mesh grids are discussed. It is shown that the average areas covered by protective actions are only negligibly affected by model refinements. (U.K.)