Individual and collective dose due to water-borne releases from Swedish nuclear facilities

Presented here is a general discussion together with examples of various factors influencing the individual- and collective-dose commitments resulting from releases of radioactive substances in liquid effluents from Swedish nuclear power plants and the Studsvik research station. A detailed study is underway to form a basis for the plant owner's reporting of releases in norm fractions to the National Radiation Protection Institute, according to the new release limits which are to come into effect in 1981. The facilities are situated at five different sites along the coasts resulting in considerable dispersion in the recipient waters. Release figures are variable for different plants and for different years but are generally in the range of 1-20 Ci(0.04-0.7 TBq) for beta/gamma-emitting nuclides and within 10-300 Ci(0.4-10 TBq) for tritium per year and site. About 25 different nuclides have been identified. To calculate dispersion and radiation doses, models and computer codes applicable to local, regional and global areas have been developed. The exposure pathways under study are consumption of fish and other marine foodstuffs, swimming, sun bathing, handling of fishing gear, and flooding of pasture land. Dose-dominant are caesium isotopes due to fish consumption. A release of 1 Ci(37 GBq) 137Cs will, for example, give a dose commitment in the order of 0.2 mrem (2μSv) to individuals in the critical group when the analytical models are used. Observed concentrations in fish indicate that the real doses are still lower. The major part of the 500-year truncated collective-dose commitment also seems to be due to caesium isotopes. A release of 1 Ci(37 GBq) 137Cs to the Baltic Sea will give, according to the preliminary results obtained with a three-zone approach, a collective-dose commitment of about 2 man.rem (0.02 man.Sv). The major part of the dose is due to exposure within the Baltic Sea zone. (author)