Application of RESRAD-OFFSITE code for coastal nuclear facility decommissioning: marine exposure pathway analysis

RESRAD-OFFSITE is a widely used radiation dose assessment code for deriving cleanup criteria and evaluating site release conditions when a nuclear facility is being decommissioned. Its application to coastal nuclear facilities is problematic because it does not consider ingestion of marine products. This study proposes a way to modify RESRAD-OFFSITE so that it can be applied to coastal facilities. We introduce a new parameter, the Seawater Exchange Rate, to quantify the effect of dilution of radioactive materials in the marine environments. We used a three-dimensional ocean model to simulate an idealized coastal area and calculated the Seawater Exchange Rate. We incorporated the obtained Seawater Exchange Rate into RESRAD-OFFSITE's lake submodel (surface water body submodel) and confirmed its validity. Calculations we made at a model site revealed that consideration of dilution via seawater exchange reduced the radiation dose associated with ingestion of marine products. Although this methodology effectively incorporates pathways involving ingestion of marine products using RESRAD-OFFSITE's existing capabilities, implementation of a marine submodel with a Seawater Exchange Rate as a parameter would streamline its practical application.