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

Abstract

The mechanism behind the dispersion of radionuclides released from the Fukushima Dai-ichi Nuclear Power Plant on March 2011 is investigated using a numerical model. This model is a Lagrangian particle tracking–ocean circulation coupled model that is capable of solving the movement and migration of radionuclides between seawater, particulates, and bottom sediments. Model simulations show the radionuclides dispersing rapidly into the interior of the North Pacific once they enter a meso-scale eddy. However, some radionuclides also remain near the coast, with spatial distribution depending strongly on the oceanic circulation during the first month after the release. Major adsorption to bottom sediments occurs during this first month and many of these radionuclides remain on the sea floor once they are adsorbed. Model results suggest that weak offshore advection during the first month will increase the adsorption of radionuclides to bottom sediments and decelerate the dispersion to the open ocean. If vertical mixing is weak, however, fewer radionuclides reach the sea floor and adsorb to bottom sediments. More radionuclides will then quickly disperse to the open ocean

Ocean dynamic processes causing spatially heterogeneous distribution of sedimentary caesium-137 massively released from the Fukushima Daiichi Nuclear Power Plant

“…Nevertheless, the value used in other studies (e.g. Kobayashi et al, 2007;Choi et al, 2013) had a wide range (O(10 −1 -10 2 ) m day −1 ). Although w p of the fine particulate matter is also known to be variable depending on its concentration (e.g.…”

“…The model was based on the following advection-diffusion-reaction equations that were used in several studies (e.g. Kobayashi et al, 2007;Periáñez, 2008;Choi et al, 2013) with the same threedimensional grid as in the hydrodynamic model: where F represents the unsteady advection-diffusion terms, expressed as…”

“…Periáñez, 2003aPeriáñez, , b, 2004Periáñez, , 2008Kobayashi et al, 2007;Monte et al, 2009). Other numerical studies (Periáñez et al, 2012;Choi et al, 2013) simulated spatiotemporal variation in sedimentary 137 Cs after the 1FNPP accident using such comprehensive models. However, they did not discuss the hotspot swath.…”

“…The reason why we used this assumption was not only because spatiotemporal variation of sediment properties just after the tsunami disturbance was unknown but also because the assumption enabled direct simulation of vertical 137 Cs behaviour in the sediment. This type of assumption has also been used in other models (Kobayashi et al, 2007;Choi et al, 2013), except for the 137 Cs behaviour in sediment. Our earlier simulations using the developed model agreed reasonably well with the sampling of 137 Cs activity in both seawater and sediment off eastern Japan in the Pacific during March and December 2011.…”

Global 7 km mesh nonhydrostatic Model Intercomparison Project for improving TYphoon forecast (TYMIP-G7): experimental design and preliminary results

“…High-resolution regional atmospheric simulations have been conducted to investigate the influence of the choice of cloud microphysics scheme and in-cloud turbulence on cloud development (Onishi et al, 2011(Onishi et al, , 2012. MSSG-O with a 2 km horizontal resolution has been used to investigate the dispersion of radionuclides released from the Fukushima Daiichi nuclear power plant (Choi et al, 2013) and the effect of wind on long-term summer water temperature trends in Tokyo Bay, Japan, with 200 m horizontal resolution (Lu et al, 2015). MSSG-A with a 5 m spatial resolution has been used in building-resolving urban atmosphere simulations to examine the heat environments of streets .…”