Report for project SSM2022-4035
SSM perspective
Background
C-14 occurs in the environment at background levels resulting from natural production and atmospheric testing of nuclear weapons, which were mainly carried out during the 1950s and 1960s. C-14 is an important radionuclide from a radiation protection point of view as it often dominates the dose to the public from activities such as operation of nuclear power plants, reprocessing of spent nuclear fuel and storage of radioactive waste, etc.
Unlike most other radionuclides (which are often metals), redistribution and accumulation in the marine ecosystems of C-14 cannot be described as easily with a distribution coefcient (Kd). Carbon (C), and thus the radionuclide C-14, is highly bioavailable and taken up during photosynthesis by primary producers
(phytoplankton and macro algae). From the primary producers, the C-14 is transferred to other parts of the marine ecosystem. In addition to being biologically active, C-14 is also part of the seasonal carbonate cycle in the sea and is controlled by the seawater’s seasonal variations in temperature, pH, etc., and thus a varying exchange of carbon (C-14) between sea surface and air. Due to a general lack of data regarding C-14 in the environment around nuclear facilities, the possibilities to validate dose models for C-14 in general are limited.
In this project a one-year study has been conducted regarding the marine radioecology of waterborne C-14 discharges from Ringhals nuclear power plant (NPP). The sampling sites were selected from the regular environmental monitoring programme at Ringhals NPP, and covered the coastal area from up to ~9 km north to ~8 km south of the NPP´s cooling water outlet. The sample types and organisms were biofouling plates, Fucus vesiculosus (bladderwrack), Symphodus melops (corkwing wrasse), Mytilus edulis (blue mussel), Magallana gigas (pacifc oyster), Cancer pagurus (crab), sediment and particulate carbon.
The report also includes a comprehensive description of sources of C-14, the fate of C-14 in the marine environment and previous studies of the radioecology of C-14.
Results
The C-14 results from the study demonstrate that, although the liquid discharges from the Ringhals Nuclear Power Plant (NPP) are assumed to be small compared to the total operational C-14 releases, the resulting C-14 levels in marine biota can be substantially higher than in terrestrial biota. The fndings indicate that the chemical speciation of discharged C-14 plays a critical role in its transfer and uptake by marine organisms.
The highest concentrations of C-14 were observed near the cooling water outlet of the NPP. Organisms collected from a biofouling plate exhibited F14C1 values up to approximately 700% above the estimated marine background. Similarly, soft tissue from Symphodus melops (corkwing wrasse) showed up to ~400% excess, Mytilus edulis (blue mussel) up to ~170%, and Fucus vesiculosus (bladderwrack) up to ~100%.
Relevance
These results provide important insights for the Swedish Radiation Safety Authority (SSM) regarding the environmental behavior of C-14, particularly in aquatic ecosystems. They suggest that current monitoring practices—based solely on airborne C-14 emissions—may underestimate the actual radiological impact in the marine environment.
The study supports the need to reconsider whether C-14 should be routinely included in environmental monitoring programs for aquatic discharges and whether it should be required to account for the chemical form and pathway of C-14 releases in the
monitoring. This knowledge is particularly relevant for ensuring the protection of the public and of marine ecosystems due to C-14 importance as a major contributor to dose.
Need for further research
Further studies in variations and chemical form in the liquid discharges from nuclear power plants of C-14 in addition to uptake to marine organisms is of interest for further research. There is also a need to evaluate the signifcance of the results for
radiological risk assessment of biota and the public.