Assessment of soil-soil solution distribution coefficients of global fallout 237Np and 239Pu in Japanese upland soils

Neptunium-237 and 239Pu are important radionuclides in the safety assessment related to geological disposal of radioactive waste because of the possibility of long-term exposure to humans. Mobilities of these radionuclides in the environment are of particular importance for their radiation dose evaluation; therefore, in this study, we have made the assessment of the soil-soil solution distribution coefficient (Kd, L/kg) using global fallout 237Np and 239Pu in Japanese upland soils. The Kd values were determined by extracting these radionuclides from 24 soil samples using a laboratory batch method. The desorption Kd values of 237Np ranged from 3.3 x 102 to 1.0 x 104 L/kg, and their geometric mean (GM) and arithmetic mean (AM) were 1.7 x 103 L/kg and 2.6 x 103 L/kg, respectively. The desorption Kd values of 239Pu were found to vary from 9.4 x 103 to 7.1 x 104 L/kg, and their GM and AM were 3.3 x 104 L/kg and 4.0 x 104 L/kg, respectively. In Japanese upland soils, the Kd value of 239Pu was one order of magnitude higher than that of 237Np.

Automated summary

In this study, the soil-soil solution distribution coefficient (Kd, L/kg) of 237Np and 239Pu in Japanese upland soils were assessed. The results showed that the Kd value of 239Pu was one order of magnitude higher than that of 237Np in Japanese upland soils.