Initial spread of <sup>137</sup>Cs from the Fukushima Dai-ichi Nuclear Power Plant over the Japan continental shelf: a study using a high-resolution, global-coastal nested ocean model Academic Article uri icon


  • <p><strong>Abstract.</strong> The 11 March 2011 tsunami triggered by the M9 and M7.9 earthquakes off the T?hoku coast destroyed facilities at the Fukushima Dai-ichi Nuclear Power Plant (FNPP) leading to a significant long-term flow of the radionuclide <sup>137</sup>Cs into coastal waters. A high-resolution, global-coastal nested ocean model was first constructed to simulate the 11 March tsunami and coastal inundation. Based on the model's success in reproducing the observed tsunami and coastal inundation, model experiments were then conducted with differing grid resolution to assess the initial spread of <sup>137</sup>Cs over the eastern shelf of Japan. The <sup>137</sup>Cs was tracked as a conservative tracer (without radioactive decay) in the three-dimensional model flow field over the period of 26 March–31 August 2011. The results clearly show that for the same <sup>137</sup>Cs discharge, the model-predicted spreading of <sup>137</sup>Cs was sensitive not only to model resolution but also the FNPP seawall structure. A coarse-resolution (&amp;sim;2 km) model simulation led to an overestimation of lateral diffusion and thus faster dispersion of <sup>137</sup>Cs from the coast to the deep ocean, while advective processes played a more significant role when the model resolution at and around the FNPP was refined to &amp;sim;5 m. By resolving the pathways from the leaking source to the southern and northern discharge canals, the high-resolution model better predicted the <sup>137</sup>Cs spreading in the inner shelf where in situ measurements were made at 30 km off the coast. The overestimation of <sup>137</sup>Cs concentration near the coast is thought to be due to the omission of sedimentation and biogeochemical processes as well as uncertainties in the amount of <sup>137</sup>Cs leaking from the source in the model. As a result, a biogeochemical module should be included in the model for more realistic simulations of the fate and spreading of <sup>137</sup>Cs in the ocean.</p>

publication date

  • August 14, 2013