Summary
In this report, the Swedish Radiation Safety Authority (SSM) presents an analysis of potential radiological consequences arising from a postulated event involving a nuclear-powered vessel occurring at a location in Sweden that is not known in advance. The analysis includes estimation of the source term and a statistical evaluation of results from dispersion and dose calculations, with the aim of estimating radiation doses to members of the public. In order to address the potential consequences of a more severe release, an extended event is also analysed.
Potential doses and the need for protective actions are analysed, and the report also presents a proposal for emergency planning that responsible authorities can use as a planning basis. In addition to measures within the scope of civil protection and remediation, potential impacts on food production are also described.
In summary, sheltering indoors within approximately one kilometre is expected to be sufficient to keep doses to the public low. In the case of a larger release, evacuation or the establishment of a maritime exclusion zone around a potential place of refuge may be required within approximately 2 km in order to meet the reference levels established in Swedish radiation protection regulations. Sheltering may also be warranted out to distances of approximately 10 km. Impacts on food production may occur over larger areas where activity concentrations in foodstuffs could exceed applicable regulatory limits.
The report includes a position on the need for iodine thyroid blocking for this type of event. Overall, SSM assesses that it is not warranted to plan for the distribution of stable iodine to the general public as a protective action for an event involving a nuclear-powered vessel where the location is not known in advance, either through pre-distribution along the Swedish coastline or through distribution during an emergency. The radiological protection benefit is considered to be relatively limited in relation to the effectiveness, cost and feasibility of such an approach.
The scope of the report is limited to emergencies occurring at locations that are not known in advance. If one or more locations in Sweden are designated to receive visits from allied nuclear-powered vessels, the situation would differ and site-specific emergency planning may be required. Such arrangements are outside the scope of this report.