SOIL–SOIL SOLUTION DISTRIBUTION COEFFICIENT OF RADIOIODINE IN SURFACE SOILS AROUND SPENT NUCLEAR FUEL REPROCESSING PLANT IN ROKKASHO, JAPAN

Abstract

Abstract The soil-soil solution distribution coefficient (Kd) of radioiodine in soil samples with various total carbon (TC) contents was measured in a batch sorption experiment using 125I tracer spiked as I−. The log values of Kd−125I and TC concentration in low-TC soils (< 10g kg−1) were positively correlated, whereas those of Kd−125I in TC rich soils (> 10 g kg−1) and dissolved organic carbon (DOC) in liquid phase were negatively correlated. The proportion of 125I in the < 3 kDa fraction in the liquid phase is negatively correlated with the log of DOC, implying that 125I is primarily combined with high-molecular-weight organic matter in soil solutions rich in DOC. The results suggest that Kd−125I in soil with high soil organic material (SOM) content is governed by DOC via the combination of 125I and DOC. In contrast, Kd−125I in soils with a low SOM content was governed by SOM because the anion exchange capacity of SOM was vital for the sorption of 125I−.