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.Ministerio de Ciencia, Innovación y Universidades PGC2018-094546-B-I00Junta de Andalucía US-126336
