Public dose assessment for Yangjiang nuclear power plant effluents: A multi-media numerical model of tritium transport in the South China sea

Periodic discharges from nuclear power plant (NPP) influence tritium background levels in seawater. After the Fukushima nuclear accident, radioactive wastewater discharges have introduced substantial amounts of tritium into the ocean. These events potentially threaten marine ecosystems and human health. To overcome the limitations of existing models, such as incomplete media consideration and low precision, we developed the TrOSB model (Tritium Ocean-Sediment-Biota transport Model). This high-precision model comprehensively analyzes transport and transformation across multiple marine media, including transport in seawater, interactions with sediments, transfer through the food chain, and assessment of public dose risks from seafood consumption. Results indicate that during the quarterly discharges of the Yangjiang NPP from 2019 to 2021, tritium from effluents spread across the entire South China Sea within four months, showing distinct seasonal transport patterns. Tritium concentrations in sediments were approximately ten times lower than those in near-bottom waters, with no significant enrichment observed in sediments. Organically bound tritium (OBT), the form of tritium transferred through the food chain, was found to be enriched to a higher degree in fish than in molluscs and crustaceans. The dose assessment indicates that public health risks from tritium in Yangjiang NPP effluents are negligible.