Regional and global contributions of anthropogenic iodine-129 in monthly deposition samples collected in North East Japan between 2006 and 2015

Publication date: May 2017
Source:Journal of Environmental Radioactivity, Volume 171
Author(s): Hidenao Hasegawa, Hideki Kakiuchi, Naofumi Akata, Yoshihito Ohtsuka, Shun'ichi Hisamatsu
We measured the monthly atmospheric deposition flux of ¹²⁹I at Rokkasho, Aomori, Japan—the location of a commercial spent nuclear fuel reprocessing plant—from 2006 to 2015 to assess the impact of the plant on environmental ¹²⁹I levels. The plant is now under final safety assessment by a national authority after test operation using actual spent nuclear fuel. During cutting and chemical processing in test operations from April 2006 to October 2008, ¹²⁹I was discharged to the atmosphere and detected in our deposition samples. ¹²⁹I deposition fluxes largely followed the discharge pattern of ¹²⁹I from the plant to the atmosphere, and most of the deposited ¹²⁹I originated from the plant. In and after 2009, ¹²⁹I deposition fluxes decreased dramatically to reach the background level; the ¹²⁹I deposition fluxes at Rokkasho were almost the same as those at Hirosaki, where an additional sampling point was set up as a background site 85 km from the plant in 2011. The background ¹²⁹I deposition fluxes showed seasonal variation—high in winter and low in the other seasons—at both Rokkasho and Hirosaki. The results of a backward trajectory analysis of the air mass at Rokkasho suggested that reprocessing plants in Europe were the origins of the high ¹²⁹I flux in winter. The contribution of ¹²⁹I released from the Fukushima Dai-ichi Nuclear Power Plant accident to the ¹²⁹I deposition flux at Rokkasho in 2011 was small on the basis of the ¹²⁹I/¹³¹I activity ratio.

Graphical abstract

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