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

Traces of Pu isotopes originated from burnt-up fuel in Fukushima exclusion zone

The accident in Fukushima Dai-ichi Nuclear Power Plant (FDNPP) released high activity of fission and neutron activation products in the environment. Total amount of released Pu is still unknown. Estimations so far indicates that dispersion from FDNPP is about 0.01 – 0.1 % of total Pu isotopes released from Chernobyl NPP accident. This implies activity of distributed Pu (for FDNPP) at the level GBq. It is assumed that more amount might be deposited close to NPP in early April 2011. However, due to sequence of hydrogen explosion (Unit 3 contained MOX fuel rods) that caused emission of radioactive elements to the atmosphere and depending on meteorological conditions, a highly radioactive plume was moved on the north - western direction of FDNPP. As a consequence of coprecipitation on 15 March 2011, a large area was affected by wet deposition. The highly contaminated area, within 30 km radius of FDNPP was defined as an exclusion zone. This work focused on Pu isotopes as traces of non-volatile elements of burnt-up fuel which were dispersed and could be deposited on that area. Previous papers reported no significant increase of 239+240Pu activity and rather rarely provided information on 238Pu activity concentration in samples from exclusion zone. In the present studies, hot spots (places with high dose rate above 2 μSv h-1) in Namie district were selected. Samples of upper layer soil and plants were collected as well as mud from small “artificial collectors” of water like e.g. small dips below downspout of rain gutter, trench that was a part of road drainage system and dips in the road, etc. The activity level of caesium isotopes (134Cs, 137Cs) in collected samples reached value 5 MBq kg-1 (signature of high and relatively fresh contamination) while 239+240Pu and 238Pu reached 0.3 Bq kg-1 and 0.5 Bq kg-1, respectively. These values were significantly higher than average activity concentration of Pu in Japanese soil estimated as a 0.15 Bq kg-1. The activity ratio, 238Pu and 239+240Pu used as a sources marker, was determined as a 0.5 for Chernobyl accident. Our study reveals higher level of Pu activity ratio in some samples in exclusion zone. That indicates very well the nuclear burnt-up fuel non-volatile elements impact on sampling area. More results in details and their interpretation will be presented at the conference.Plutonium Futures-The Science 201

NATURALLY OCCURRING RADIONUCLIDES AND SELECTED RARE EARTH ELEMENTS IN AIR PARTICULATES OF AN INDIAN HIGH RADIATION BACKGROUND AREA

Naturally occurring radionuclides of terrestrial origin are present in the earth’s crust. In most places on the earth, the natural radioactivity varies only within narrow limits, but in some places there are wide deviations from normal levels because of abnormally high levels of radioactive minerals. The presence of thorium and uranium and their decay products in minerals such as monazites, ilmenite, rutile, silimanite and zircon result in enhanced natural background radiation fields in the deposit areas are widely known as high background radiation area (HBRA). Monazite is one of the principal sources of rare earth elements (REEs) and present in the continental crust. Thus it is necessary to facilitate data on HBRAs to predict radiation patterns in the environment toincrease awareness. Radiological investigations have been carried out in the eastern coastal area of Odisha state, India to measure the extra terrestrial gamma dose rate, natural radionuclide (226Ra, 228Ac and 40K) concentration in selected surface soil samples. Based on thoron and its progeny measurements in the houses, air particulates were collected using cascade impactor. REEs, U and Th were measured from air particulates using an inductively coupled plasma mass spectrometry (ICP-MS) for a better understanding to trace the origin of sources.9th International Conference on High Level Environmental Radiation Areas-For Understanding Chronic Low-Dose-Rate Radiation Exposure Health Effects and Social Impacts (ICHLERA 2018

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

Measurement of 90Sr in soil samples affected by the Fukushima Daiichi Nuclear Power Plant accident

Strontium 90 activity concentration was measured in four soil samples (0-10 cm) collected from the exclusion zone around the Fukushima Daiichi Nuclear Power Plant (FDNPP). The open chemical digestion method was used for sample decomposition with a mixture of acids. The strontium separation was achieved with strontium selective resin (Sr-resin). The activity of strontium 90 was determined with liquid scintillation counter (LSC). Owing to the atmospheric nuclear weapon tests, the soil in Japan is contaminated with strontium 90. Related to this background level, significant Fukushima contamination was not noticed by the results of this study. The detected strontium 90 activities were 8.9±0.8, 20±1.3, <6.8, and 23.4±1.5 Bq kg-1, respectively