The transport, effective half-lives and age distributions of radioactive releases in the northern Indian Ocean

A Lagrangian model which describes radionuclide transport in the northern Indian Ocean is described. Water circulation is obtained from HYCOM ocean model for year 2017. The model includes advection by currents, turbulent mixing and radionuclide interactions between water and sediments, described in a dynamic way using kinetic transfer coefficients. Hypothetical releases from five coastal nuclear power plants operating in the northern Indian Ocean were simulated. Releases were supposed to start both during the winter and summer monsoons, to study reversing circulation effects. Age distributions of releases were calculated, which adds information about circulation and radionuclide pathways. It was found that, for some of the NPPs, radionuclide distributions resulting from releases starting in both seasons were not as different as could be expected from the opposed circulation schemes during each monsoon. Effective 137Cs half-lives in the ocean surface were calculated and results were two orders of magnitude below previous estimations.