Chemical forms of inorganic 129I originating from the spent nuclear fuel reprocessing plant observed off Rokkasho, Aomori Prefecture

This study analyzed the chemical speciation and characteristics of inorganic 129 I and 127 I in seawater collected off the coast of Rokkasho, Aomori Prefecture, Japan. The atomic ratios for each species were as follows: ( 129 I − + 129 IO 3 − )/( 127 I − + 127 IO 3 − ), 6.1–13.1 × 10 −11 ; 129 I − / 127 I − , 11.0–74.1 × 10 −11 ; and 129 IO 3 − / 127 IO 3 − , 3.3–5.9 × 10 −11 . At several stations, elevated values were detected from the surface to a depth of 20 m, which likely reflected the influence of the effluent. 129 I discharged from the nuclear fuel reprocessing plant was primarily present as dissolved 129 I − , and no significant oxidation of 129 I − to 129 IO 3 − was observed 13 days after discharge. Furthermore, 129 I supplied by riverine inputs was also present predominantly as dissolved 129 I − .