Concentration of ¹²⁹I of aquatic organisms in brackish lake and coastal area

The spent nuclear fuel reprocessing plant in Rokkasho, Japan, has been undergoing final testing since March 2006. During April 2006-October 2008, that spent fuel was cut and chemically processed, the plant discharged ¹²⁹I into the atmosphere and coastal waters. The concentrations of ¹²⁹I in aquatic biota samples from brackish lakes and coastal ocean around the reprocessing plant were measured from 2005 to 2012. Owing to ¹²⁹I discharge from the plant, the ¹²⁹I concentration in the biota in brackish lake started to rise from the background concentration in 2006 and was high during 2007-2008. The ¹²⁹I concentration has been rapidly decreasing after the fuel cutting and chemically processing was finished. Using these results, the apparent concentration factor (CF) was determined assuming that iodine (¹²⁹I and ¹²⁷I) was in equilibrium between the lake (sea) water and the aquatic biota. The CF of ¹²⁹I in many species of aquatic biota were in the range of values reported by the IAEA, etc., but values differed depending on species of biota. Since the CFs of ¹²⁹I and ¹²⁷I in aquatic biota were almost similar, assuming that ¹²⁷I as a stable isotope is in equilibrium between the lake (coastal) water and biota, it is judged that ¹²⁹I is also almost in equilibrium. (author)