MEASUREMENT OF URANIUM ISOTOPES AND ITS DISTRIBUTION COEFFICIENT IN FUKUSHIMA CONTAMINATED SOILS TO UNDERSTAND MOBILITY

Fukushima Daiichi Nuclear Power Plant (FDNPP) accident caused radioactive contamination due to deposition of mainly radiocesium as well as many long-lived radionuclides surrounding the area[1]. Radionuclides can be mobilized in aquatic systems depending on different environmental conditions, Therefore, the fate and transfer of these radionuclides in the soil water system plays an important role in radiation protection and dose assessment. \nIn 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 uranium 234U/238U (activity ratio) and 235U/238U using thermal ionization mass spectrometry (TIMS) that gives us the idea about its contamination during accident. \nFor the migration behavior, its distribution coefficient (Kd) has been determined using laboratory batch method [2]. Chemical characterization of soil with respect to different parameters has been carried out in order to explain the radionuclide mobility in this particular area. 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 1600-9000 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 pH, Fe, Mn, CaCO3 and organic content. There is a very good correlation of uranium Kd obtained with Fe content. There is a variation with uranium activity ratio where as no enrichment of 235U has been noticed in the studied area. However contaminated water used for cooling the reactor vessel stored near the reactor after accident, may contain radioactive uranium. Therefore, it is of a concern to understand leaching of U in the groundwater system. \n[1]P. Povinec, K. Hirose, M. Aoyama, “Fukushima Accident: Radioactivity impact on the environment” (2013). [2]S. Mishra, et al., Rad. Prot. Dosim. 152:238 (2012).16th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere (MIGRATION 2017)

Reprint of "Vertical migration of radio-caesium derived from the Fukushima Dai-ichi Nuclear Power Plant accident in undisturbed soils of grassland and forest"

The vertical distribution of radio-caesium (137Cs and 134Cs) in undisturbed soil profiles of grassland and forest soils, derived from the Fukushima-Daiichi Nuclear Power Plant (FDNPP) accident that occurred on 11 March 2011, was studied. Surface soil and depth profile soil samples were collected from six locations within the 20 km zone of FDNPP, during November 2012 and June 2013. The activity ratio for 137Cs and 134Cs was found to be almost constant about 1 within the soil profiles as well as in the surface soil, indicative of FDNPP accident origin. From soil depth profile distribution of Cs activity, it is observed that Cs is strongly bound to soil materials, which slows Cs migration. N90% of the activity was found to be retainedwithin the upper 5 cmlayer. Retardation of Cs movement has been quantified by measuring sorption of Cs in soil in terms of distribution coefficient (Kd) using the laboratory batch method. Faster migration has been observed in case of forest land soil compared to grassland soil. The empirical migration velocity of Cs radio isotope was estimated fromthe depth profile Cs concentrationand found to vary from 1.1 to 1.7 and 0.85 to 3.5 cm y−1 in grassland and forest soil, respectively. The residential half life for Cs isotopes was found to be 1.03–7.75 y and 1.18–4.67 y for grassland and forest land respectively using a compartmental model. In addition to the empirical analysis of the profiles, analytical modelswere fitted to the data which may help elucidate the physical nature of the transport of trace elements

Measurement and validation of uranium isotope ratio in uranium ore for isotopic fingerprinting

Accurate determination of uranium isotope ratio can act as an efficient fingerprint in the nuclear forensics to identify source and intended use of illicit trafficking of uranium material. In this context, a rapid chemical separation technique to isolate uranium from uranium ore sample was developed using commercialextraction chromatographic resin. Uranium isotope ratio was measured using thermal ionization mass spectrometry (TIMS). Standard reference material (NBS U010) was used for validating the accuracy and precision of isotope ratio measurement by TIMS. The method is successfully applied to a natural ore(uraninite ore) for the determination of naturally occurring uranium isotope ratio

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

ESTIMATION OF URANIUM ISOTOPES IN SOIL AFFECTED BY FUKUSHIMA NUCLEAR POWER PLANT ACCIDENT AND ITS MOBILITY BASED ON DISTRIBUTION COEFFICIENT AND SOIL PROPERTIES

An extraordinary earthquake of magnitude 9.0 followed by Tsunami on 11 March 2011 caused serious nuclear accident occurred at the Fukushima Daiichi Nuclear Power Plant (FDNPP) about 250 km north to Tokyo, capital of Japan. This has resulted radioactive contamination in a large area due to deposition of long-lived radionuclides. Contaminated soil can cause an enhanced radiation exposure even after many years and depending upon environmental conditions can be mobilized to 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, emphasis has been given on isotope ratio measurement of uranium which can give us the idea about its contamination during accident. Soil and water samples were collected from contaminated areas around FDNPP. Inductively coupled plasma mass spectrometry (ICPMS) is used for total uranium concentration and thermal ionization mass spectrometry (TIMS) has been used for uranium isotopes measurement. Extraction chromatography has been used for the separation of uranium. We have observed, isotope ratio 235U/238U is of natural origin, however in a few soil samples 236U has been detected. For the migration behavior, its distribution coefficient (Kd) has been determined using laboratory batch method. Depleted uranium is used as tracer for uranium Kd estimation. 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 30-35679 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 pH, Fe, Mn, CaCO3 and organic content. There is a very good correlation of uranium Kd obtained with Fe content. There is a variation with uranium activity ratio where as no enrichment of 235U has been noticed in the studied area. However contaminated water used for cooling the reactor vessel stored near the reactor after accident, may contain radioactive uranium. Therefore, it is of a concern to understand leaching of U in the groundwater system. In that context, this study will be very much useful.International Conference on RADIOECOLOGY & ENVIRONMENTAL RADIOACTIVITYに参加し、ESTIMATION OF URANIUM ISOTOPES IN SOIL AFFECTED BY FUKUSHIMA NUCLEAR POWER PLANT ACCIDENT AND ITS MOBILITY BASED ON DISTRIBUTION COEFFICIENT AND SOIL PROPERTIESの発表を行