Inventory of 129 I in brackish lake sediments adjacent to a spent nuclear fuel reprocessing plant in Japan

The 129I inventory in sediment of brackish lake, beside a nuclear fuel reprocessing plant in Rokkasho, Japan, was clarified from 1997 to 2016. The 129I was discharged to the atmosphere and ocean during cutting and chemical processing the spent fuel in the test operation from April 2006 to October 2008, although the plant is under final safety assessment as of May 2018. The 129I concentration and 129I/127I ratio in the surface sediment were 5–6 and 4–5 times higher than those in 1997, respectively. The 129I to a depth of 25 cm in the sediment increased until 2010–2012, then stabilized with accumulated state.