Effects of different accident scenarios and sites on the reduction factor used for expressing sheltering effectiveness

Public living in areas contaminated by nuclear accidents is exposed to radiation in the early phase and over the long term. Even under similar accident scenarios, radiation doses and sheltering effectiveness, which is one of the protective measures, depend on meteorological conditions and the surrounding environment. Radiation doses and sheltering effectiveness in the early phase of nuclear accidents are crucial information for the public as well as national and local governments planning a nuclear emergency preparedness. In this study, we assessed radiation doses and sheltering effectiveness at sites with nuclear facilities in Japan using the Off-Site Consequence Analysis code for Atmospheric Release accidents, which is one of the level-3 probabilistic risk assessment codes, for five accident scenarios: three scenarios from past severe accident studies, a scenario defined by the Nuclear Regulation Authority in Japan, and a scenario corresponding to the Fukushima-Daiichi Nuclear Power Station accident. The sheltering effectiveness differed by up to approximately 50% among the accident scenarios at the same sites and by approximately 20%-50% among sites under the same accident scenario. Differences in the radionuclide composition among the accident scenarios and the differences in wind speeds among the sites primarily caused these differences in sheltering effectiveness.