Desorption coefficients of ²³⁹Pu and ²³⁷Np in Japanese paddy field soils

²³⁹Pu and ²³⁷Np are long-lived radionuclides that emit alpha rays, and once released into the environment, they will exist in the environment for a long period of time. Therefore, ²³⁹Pu and ²³⁷Np are important radionuclides in the safety assessment related to geological disposal of radioactive waste because of the possibility of long-term exposure. Regarding the partition coefficient (K_d) for actinides such as ²³⁹Pu, for sand, minerals, and overseas soil, the adsorption K_d data through the RI tracer experiment has been obtained to some extent, but on the other hand, K_d data on agricultural soils in Japan are still scarce. In this study, for the first time, the determination of desorption K_d for ²³⁹Pu and ²³⁷Np has been carried out using a laboratory batch method. A comparison between the obtained K_d of ²³⁹Pu and ²³⁷Np indicated that ²³⁹Pu K_d was about one order of magnitude higher than ²³⁷Np in Japanese paddy field soils. (author)