Radioecology of 14C in the marine environment of Ringhals nuclear power plant

arbon-14 (14C) is of special interest for dose assessments related to operational releases from the nuclear industry as it is the radionuclide that normally dominates the committed effective dose to the public. For normal operation of nuclear power plants (NPPs), liquid 14C effluents are significantly less than airborne releases. However, dispersion in the environment is very different in water bodies than in the atmosphere. Therefore, significantly increased levels compared to background may be seen in the aquatic environment of nuclear reactors. The dosimetric importance of 14C in water-borne releases is demonstrated in the new SSM regulations SSMFS2021:6, valid from 1 March 2022: source monitoring of water-borne 14C discharges from NPPs is now required.
Translating the discharged amount of activity into the coastal waters and further on to the seas and oceans into committed effective dose to humans, requires detailed knowledge of the radioecology of 14C. However, there are still significant knowledge gaps for the radioecological behaviour of anthropogenic 14C released from e.g. nuclear facilities. The marine radioecology of 14C is complicated and probably site-specific, as it is strongly influenced by local carbon and water cycles: the use of generic transfer factors and distribution coefficients for 14C are believed to be insufficient. Site-specific radioecological investigations are therefore required to support the development of suitable radioecological models, and to assess the actual radiological impact of this radionuclide.
This project proposal aims to produce data to understand the radioecological fate of 14C at the Swedish NPPs. It will include investigations for determining the proportion that foreign nuclear facilities influence the varying Swedish marine 14C background, it will study long-term trends and temporal variations in the marine 14C background, and radioecological in situ studies will be performed at Ringhals NPP. In total ~180 samples will be analysed for the content of 14C using Accelerator Mass Spectrometry (AMS). Stable isotope mass spectrometry (δ13C and δ15N) will be used to provide further information on e.g. environmental conditions, plant life cycle and trophic level. Competence for 14C analysis of various biogeochemical carbon fractions such as dissolved inorganic carbon (DIC) and particulate organic carbon (POC) in water will be developed at Lund University. 129I and 99Tc analysis will aid the apportionment of foreign sources of 14C on the Swedish west coast. The data obtained in the project will be of great importance for correct dose assessment of 14C from the nuclear power industry and SSM. It will contribute with novel, coveted knowledge on the marine radioecology with high international academic relevance. The project will use newly collected samples and also samples from the unique long-time biobank of Fucus samples (the historical Särdal series, consisting of Fucus samples collected for over 50 years by Emeritus Professor Sören Mattsson). The project will also preserve this biobank for future investigations.