Vertical distributions of plutonium isotopes in marine sediment cores off the Fukushima coast after the Fukushima Dai-ichi Nuclear Power Plant accident

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident led to the release of large amounts of radionuclides into the atmosphere as well as direct discharges into the sea. In contrast to the intensive studies on the distribution of the released high volatility fission products, such as 131I, 134Cs and 137Cs, similar studies of the actinides, especially the Pu isotopes, are limited. To obtain the vertical distribution of Pu isotopes in marine sediments and to better assess the possible contamination of Pu from the FDNPP accident in the marine environment, we determined the activities of 239+240Pu and 241Pu as well as the atom ratios of 240Pu/239Pu and 241Pu/239Pu in sediment core samples collected in the western North Pacific off Fukushima from July 2011 to July 2012. We also measured surface sediment samples collected from seven Japanese estuaries before the FNDPP accident to establish the comprehensive background baseline data. The observed results of both the Pu activities and the Pu atom ratios for the sediments in the western North Pacific were comparable to the baseline data, suggesting that the FDNPP accident did not cause detectable Pu contamination to the studied regions prior to the sampling time. The Pu isotopes in the western North Pacific 30 km off Fukushima coast originated from global fallout and Pacific Proving Ground close-in fallout

First determination of Pu isotopes (239Pu, 240Pu and 241Pu) in radioactive particles derived from Fukushima Daiichi Nuclear Power Plant accident

Radioactive particles were released into the environment during the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Many studies have been conducted to elucidate the chemical composition of released radioactive particles in order to understand their formation process. However, whether radioactive particles contain nuclear fuel radionuclides remains to be investigated. Here, we report the first determination of Pu isotopes in radioactive particles. To determine the Pu isotopes (239Pu, 240Pu and 241Pu) in radioactive particles derived from the FDNPP accident which were free from the influence of global fallout, radiochemical analysis and inductively coupled plasma-mass spectrometry measurements were conducted. Radioactive particles derived from unit 1 and unit 2 or 3 were analyzed. For the radioactive particles derived from unit 1, activities of 239+240Pu and 241Pu were (1.70-7.06)×10-5 Bq and (4.10-8.10)×10-3 Bq, respectively and atom ratios of 240Pu/239Pu and 241Pu/239Pu were 0.330-0.415 and 0.162-0.178, respectively. These ratios were consistent with the simulation results from ORIGEN code and measurements from various environmental samples. In contrast, Pu was not detected in the radioactive particles derived from unit 2 or 3. The difference in Pu contents is clear evidence towards different formation processes of radioactive particles, and detailed formation processes can be investigated from Pu analysis

Isotopic evidence of plutonium release into the environment from the Fukushima DNPP accident

The Fukushima Daiichi nuclear power plant (DNPP) accident caused massive releases of radioactivity into the environment. The released highly volatile fission products, such as 129mTe, 131I, 134Cs, 136Cs and 137Cs were found to be widely distributed in Fukushima and its adjacent prefectures in eastern Japan. However, the release of non-volatile actinides, in particular, Pu isotopes remains uncertain almost one year after the accident. Here we report the isotopic evidence for the release of Pu into the atmosphere and deposition on the ground in northwest and south of the Fukushima DNPP in the 20–30 km zones. The high activity ratio of 241Pu/239+240Pu (> 100) from the Fukushima DNPP accident highlights the need for long-term 241Pu dose assessment, and the ingrowth of 241Am. The results are important for the estimation of reactor damage and have significant implication in the strategy of decontamination

Reconstruction of radiocesium levels in sediment off Fukushima: Simulation analysis of bioavailability using parameters derived from observed 137Cs concentrations

Radiocesium was released to the North Pacific coastal waters by the accident at the Fukushima Dai-ichi Nuclear Power Plant (1FNPP) of the Tokyo Electric Power Company (TEPCO) in March 2011. Since the radiocesium in the sediment off Fukushima was suggested as a possible source for the transfer of this radionuclide through the benthic food chain, we conducted numerical simulations of 137Cs in sediments off the Fukushima coast by using a model which incorporates dynamic transfer processes between seawater and the labile and refractory fractions in sediment particles. This model reproduced the measured temporal changes of 137Cs concentration in seabed surface sediment off Fukusima coasts, by normalizing the radiocsium transfer between seawater and sediment according to the particle diameter sizes. We found that the 137Cs level in sediment decreased by desorption during the first several months after the accident, followed by a reduction in the labile fraction until the end of 2012. The apparent decrease of the total radiocesium level in surface sediment was estimated to occur at rates of approximately 0.2 y−1 within a 20 km distance from the 1FNPP. The comparison of 137Cs level decreases in the demersal fish and the simulated temporal labile fraction in fine sediment demonstrated that the consideration of radiocesium transfer via sediment is important for determining the 137Cs depuration mechanism in some demersal fish

Dispersion of Artificial Caesium-134 and -137 in the Western North Pacific One Month After the Fukushima Accident

In March 2011, an accident at the Fukushima Daiichi nuclear power plant (FNPP) was caused by the Tohoku earthquake and tsunami. Here we show the distribution of artificial caesium-134 and -137 (134Cs and 137Cs) in the western North Pacific one month after the FNPP accident. In surface seawater, 137Cs concentrations were from several times to two orders of magnitude higher than before the FNPP accident. 134Cs was also detected, and in many seawater samples the 134Cs/137Cs ratio was about 1. These findings indicate that radionuclides from the FNPP dispersed quickly in the western North Pacific. 134Cs and 137Cs concentrations in suspended solids and zooplankton at stations K2 and S1 were also one to two orders higher than before the accident. Numerical simulation results show that the higher caesium observed in the western North Pacific one month after the FNPP accident was transported not only by diffusion and advection of seawater but also via the atmosphere as an aerosol.Abstract presented at Ocean Sciences Meeting 2012, the Oceanography Society, ASLO, AGU, Salt Lake City, Utah, Feb. 20-24, 201

Radionuclide contamination in food and estimation of radiation doses from food intake since the Fukushima Nuclear Power Station Accident

A nuclear accident of the Fukushima Daiichi Nuclear Power Station (FDNPS) had been caused by the tsunami after the Great East Japan Earthquake in March 2011, and the huge amounts of radionuclides was dispersed around Fukushima immediately [1]. It is important that the activity concentrations of radionuclide have been continuously monitored in the territorial and marine environment due to understand the dispersion and behavior of radionuclide after the FDNPS accident. Furthermore, the effects of released radionuclides on agricultural, forest and fishery products after the FDNPS accidents have been discussed with the temporal and spatial variations of activity concentrations of radionuclide in the environment. After this accident, Nuclear Emergency Response Headquarters in Japan started the use of the provisional regulation value in food promptly (March 17, 2011-March, 2012). This concept of the limit for food and water is less than 5mSv/yr. However, it was necessary to carefully consider external and internal exposure due to the FDNPS is located in neighborhood. Based on the concept of 1mSv/yr for food and drinking water, new standard value in food (the limit of general food: 100 Bq-Cs/kg) was enforced from April1, 2012. The concentrations of radiocaesium (R-Cs) in seawater are almost same levels before the accidents except the near site of FDNPS, and these in fish generally decreased, and radiation doses from foods intake are negligible [2]. However, high concentrations of R-Cs are kept to some specific products as food as the result of nutrient cycle, accumulation, translocation and food chain. In this presentation, we would like to talk about the estimation of internal dose from food intake and the survey of consumer awareness for food in Japan with the monitoring of R-Cs in the environment after the FDNPS.3rd International Conference “RADON IN THE ENVIRONMENT2019

Seasonal variability of 230Th flux in the West Caroline Basin.

2001 Fall Meetin

Seasonal variation of 231Pa and 230Th fluxes in the West Caroline Basin

Twelfth Annual V.M.Goldschmidt Conferenc