14C in the Environment of Swiss Nuclear Installations

Abstract

The results of a 10-year survey of 14C content in tree leaves from the vicinity of Swiss nuclear installations are reported. The interpretation is based on the results from a reference station showing a systematic decrease from Delta-14C = +350 per mil in 1977 to ca +190 per mil in 1987. Excess activities of up to ca 100 per mil are observed in the vicinity of nuclear power plants which are compatible with release rates and dilution calculations. A higher excess of up to 1400 per mil is measured in the close vicinity of a small research plant which releases the activity on top of the roof. The determined decrease of the activity with distance can be described by a power law with ca -1.4 in the exponent. Additional doses of 14C to plants and population from excess 14C activities are estimated to be negligible compared to natural doses.