Measurement of uranium distribution coefficient and 235U/238U ratio in soils affected by Fukushima dai-ichi nuclear power plant accident.

Fukushima Daiichi Nuclear Power Plant (FDNPP) accident resulted radioactive contamination in soil due to deposition of mainly radiocesium as well as many long-lived radionuclides surrounding a large area around FDNPP. Depending upon environmental conditions, radionuclides in soil can be mobilized in aquatic systems. Therefore, the fate and transfer of these radionuclides in the soil water system is very important for radiation protection and dose assessment. In the present study, soil and water samples were collected from contaminated areas around FDNPP. Inductively coupled plasma mass spectrometry (ICP-MS) is used for total uranium concentration. Emphasis has been given on isotope ratio measurement of 235U/238U ratio using thermal ionization mass spectrometry (TIMS) that gives us the idea about its contamination during accident. For the migration behavior, its distribution coefficient (Kd) has been determined using laboratory batch method. Chemical characterization of soil with respect to different parameters has been carried out. The effect of these soil parameters on distribution coefficient of uranium has been studied in order to explain the radionuclide mobility in this particular area. The distribution coefficient values for uranium are found to vary from 30 to 36000 L/kg. A large variation in the distribution coefficient values shows the retention or mobility of uranium is highly dependent on soil characteristics in the particular area. This variation is explained with respect to soil pH, Fe, Mn, CaCO3 and organic content. There is a very good correlation of uranium Kd obtained with Fe content. There is no enrichment of 235U has been noticed in the studied area.