Improvement of a model for estimating radionuclide concentration in marine organisms in a marine environment exposure dose assessment model

We recently developed a marine environment exposure dose assessment model to evaluate the radiological doses to the public following marine radiological accidents. The following six exposure pathways were considered: external exposure through beach activity, swimming, and boating and internal exposure through inhalation via sea spray, ingestion of seawater during swimming and ingestion of seafood. A model for estimating radionuclide concentration in marine organisms in the present dose assessment model was developed based on the equilibrium model, taking into account realistic aspects related to food intake and data availability related to model input variables. However, when the equilibrium model was applied in the early phase of an accident in which the radionuclide concentration changes significantly, there is a possibility that the evaluation result of nuclide concentration in marine organisms could be overestimated, so a dynamic marine foodchain model was added to the equilibrium model-based marine dose assessment module so that it can be selectively applied according to the purpose of the assessment. When applying the dynamic model, the limitations of the model to the uncertainty about the input variables and assessment results due to the lack of available data must be considered. The dynamic model considered three groups of seafood (fish, invertebrate, seaweed), as in the equilibrium model. The model contains  compartments for water, sediment, and marine organism groups. The radioactivity transfer for compartments is dynamically modeled by a first-order differential equation using rate constant. Radioactive decay is considered in all compartments. To the next step, it is planning to develop a module that can evaluate the public exposure doses by linking the dose assessment model with the marine dispersion model, and apply it to the case study for calculating the public exposure following hypothetical marine radiological accidents.