Concentrations of iodine-129 in livestock, agricultural, and fishery products around spent nuclear fuel reprocessing plant in Rokkasho, Japan, during and after its test operation

摘要

Concentrations of iodine-129 (I-129) and atomic ratios of I-129/I-127 in livestock (grass and milk), agricultural (cabbage, Japanese radish, and rice), and fishery (flatfish and brown alga) products collected from locations around the first Japanese commercial spent nuclear fuel reprocessing plant in Rokkasho were measured from 2006 to 2016. The actual spent nuclear fuel rods were cut and processed to test the functioning of the plant that discharged controlled amounts of I-129 to the atmosphere and coastal seawater during the period from 2006 to 2008 (the cutting period). Statistically significant increases in I-129 concentration and I-129/I-127 ratio were observed during the cutting period in livestock products and flatfish. On the other hand, these parameters were statistically comparable during and after the cutting period in the other products. The radiation dose through the ingestion of the maximum I-129 concentrations, measured in the different products, was estimated to be in the nanoSievert per year level. This value is much smaller than 1mSvyr(1), which is the permissible authentic radiation dose for the general public. The I-129 levels in the samples, especially in milk and flatfish, are discussed in context of the I-129 discharge history from the plant.