Long-term simulation of 137Cs in the Irish Sea by using ocean environment assessment system

An ocean environment assessment system that forecasts the detailed migration processes of radionuclides in the ocean has been developed. This system consists of an ocean current model and a particle random-walk model. The ocean current model is the modified Princeton Ocean Model (POM). The POM calculates tidal currents by giving tide levels at the open boundary. The particle random-walk model, SEA-GEARN, calculates the radionuclides migration in the ocean. Radionuclides that exist in the ocean are modeled in three phases, such as dissolved in seawater, adsorbed with large particulate matter (LPM) and adsorbed with active bottom sediment. The adsorption and desorption processes between the dissolved and solid phases are solved with the kinetic transfer coefficients by the stochastic method. Deposition of LPM and resuspension from bottom sediment are also considered. As model validation, the system has been applied to the Irish Sea to simulate the long-term dispersion of 137Cs actually released from the BNFL spent nuclear fuel reprocessing plant at Sellafield in UK. Calculation results of surface dissolved 137Cs have been compared with the observed data. The observed data are extracted from a database, Marine Information System (MARIS), which is released from the International Atomic Energy Agency's Marine Environment Laboratory (IAEA-MEL) in Monaco. The calculation well reproduces the main characteristics of migration of surface dissolved 137Cs concentration in the Irish Sea. (author)