Study on distribution and behavior of long-lived radionuclides in surface soil environment

Technetium-99 (99Tc) and Neptunium-237 (237Np) are important radionuclides for environmental assessment around nuclear fuel cycle facilities, because these have long-lives and relatively high mobility in the environment. Therefore, we have been studied the determination, distribution and behavior of such long-lived radionuclides in surface soil environment. A new analytical technique using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was applied to the determination of long-lived radionuclides in environmental samples. The determination method consists of dry ashing, anion exchange and solvent extraction to eliminate the interfering elements and ICP-MS measurement. The sensitivity of this method was 10 to 100,000 times higher, and the counting time was 300 to 100,000 times shorter than the conventional radioanalytical methods. The soil samples were collected at nine points and core soil sample was collected by an electric core sampler at one point. The core soil sample was divided into eight layers. The depth profiles showed that more than 90% of 99Tc and 237Np were retained in the surface layer up to 10cm in depth which contained much amount of organic materials. The results suggest that content of organic materials in soil is related to adsorption of 99Tc and 237Np onto soil. (author)