The impact of oceanic circulation and phase transfer on the dispersion of radionuclides released from the Fukushima Dai-ichi Nuclear Power Plant

摘要

The mechanism behind the dispersion of radionuclides released from theFukushima Dai-ichi Nuclear Power Plant on March 2011 is investigated using anumerical model. This model is a Lagrangian particle tracking–oceancirculation coupled model that is capable of solving the movement andmigration of radionuclides between seawater, particulates, and bottomsediments. Model simulations show the radionuclides dispersing rapidly intothe interior of the North Pacific once they enter a meso-scale eddy.However, some radionuclides also remain near the coast, with spatialdistribution depending strongly on the oceanic circulation during the firstmonth after the release. Major adsorption to bottom sediments occurs duringthis first month and many of these radionuclides remain on the sea flooronce they are adsorbed. Model results suggest that weak offshore advectionduring the first month will increase the adsorption of radionuclides tobottom sediments and decelerate the dispersion to the open ocean. Ifvertical mixing is weak, however, fewer radionuclides reach the sea floor andadsorb to bottom sediments. More radionuclides will then quickly disperse tothe open ocean.