Vertical distribution of I released from the Fukushima Daiichi Nuclear Power Plant in the Kuroshio and Oyashio current areas

Suzuki, Takashi; Otosaka, Shigeyoshi; Kuwabara, Jun; Kawamura, Hideyuki; Kobayashi, Takuya

Marine Chemistry, 204, p.163 - 171, 2018/08

https://doi.org/10.1016/j.marchem.2018.07.007

To investigate the penetration of radionuclides released from Fukushima Daiichi Nuclear Power Plant (FDNPP), depth profiles were revealed at Kuroshio current, transition, and Oyashio current areas. The FDNPP-derived I was found in surface layer at Oyashio current and transition areas and in sub-surface layer at Kuroshio current area. Moreover, it was found that the FDNPP-derived I/Cs ratios in the Oyashio current and transition areas were higher than that in the FDNPP reactor. The higher FDNPP-derived I/Cs ratios suggest three potential mechanisms for the migration of radionuclides in the environment: (1) radioiodine was released more easily than radiocesium by the FDNPP accident, (2) I was supplied from the atmosphere by re-emitted I from contaminated areas around Fukushima, (3) leaked water that removed radiocesium reached the sampling stations. The FDNPP-derived I in sub-surface layer would be transported by the meander of the Kuroshio Extension current.