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 129I and 127I in seawater collected off the coast of Rokkasho, Aomori Prefecture, Japan. The atomic ratios for each species were as follows: (129I- + 129IO3-)/(127I- + 127IO3-), 6.1-13.1 × 10-11; 129I-/127I-, 11.0-74.1 × 10-11; and 129IO3-/127IO3-, 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. 129I discharged from the nuclear fuel reprocessing plant was primarily present as dissolved 129I-, and no significant oxidation of 129I- to 129IO3- was observed 13 days after discharge. Furthermore, 129I supplied by riverine inputs was also present predominantly as dissolved 129I-.