Activity Ratio of Caesium, Strontium and Uranium with Site Specific Distribution Coefficients in Contaminated Soil near Vicinity of Fukushima Daiichi Nuclear Power Plant

Activity concentrations of Cs radioisotopes (137Cs and 134Cs) were measured in four soil samples at the proximity of Fukushima daiichi nuclear power plant (FDNPP), located in and off the radioactive plume direction. Activity of Cs was higher than 90Sr and 238U in the plume direction. Lowest 137Cs activity was found to be 950±13Bq/kg and highest was 62,200±880 Bq/kg. In case of 90Sr, the lowest and highest activity concentrations were found to be 8.4 ± 1.5 Bq/kg and 21.2 ± 2.6 Bq/kg respectively. Activity concentration of 238U varied from 25.4±0.1Bq/kg to 45.2 ± 0.1Bq/kg. Activity ratio of 134Cs to 137Cs was in range of 0.84-0.87 measured in 2012,indicates the origin from FDNPP accident. Activity ratio of 234U/238U varied from 0.996-1.029. To establish the fate and transfer of radionuclides, site specific distribution coefficient (Kd) were measured in the soil samples using standard method. Kd values for Cs, Sr and U were found to be log Kd(Cs) ~2, logKd(Sr) ~1-2 and logKd(U) ~3. Different soil parameters like particle size distribution, pH, organic content, cation exchange capacity, CaCO3, elemental and oxide composition of soil has been carried out to understand the geochemical behaviour of these radionuclides. A good correlation was observed for Kd (Cs) and Kd(Sr) with cation exchange capacity and fine particle concentration and Kd(U) with Fe and organic content of soil