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Journal Articles

A Storm-induced flood and associated nearshore dispersal of the river-derived suspended $$^{137}$$Cs

Uchiyama, Yusuke*; Tokunaga, Natsuki*; Azuma, Kohei*; Kamidaira, Yuki; Tsumune, Daisuke*; Iwasaki, Toshiki*; Yamada, Masatoshi*; Tateda, Yutaka*; Ishimaru, Takashi*; Ito, Yukari*; et al.

Science of the Total Environment, 816, p.151573_1 - 151573_13, 2022/04

 Times Cited Count:5 Percentile:71.31(Environmental Sciences)

no abstracts in English

Journal Articles

Behavior of radiocesium in sediments in Fukushima coastal waters; Verification of desorption potential through pore water

Otosaka, Shigeyoshi*; Kambayashi, Shota*; Fukuda, Miho*; Tsuruta, Tadahiko; Misono, Toshiharu; Suzuki, Takashi; Aono, Tatsuo*

Environmental Science & Technology, 54(21), p.13778 - 13785, 2020/11

 Times Cited Count:12 Percentile:55.09(Engineering, Environmental)

Concentrations of $$^{137}$$Cs in seawater, seabed sediment, and pore water collected from the area around Fukushima were investigated from 2015 to 2018, and the potential of coastal sediments to supply radiocesium to the bottom environment was evaluated. The $$^{137}$$Cs concentration in the pore water ranged from 33 to 1934 mBq L$$^{-1}$$ and was 10-40 times higher than that in the overlying water (seawater overlying within 30 cm on the seabed). At most stations, the $$^{137}$$Cs concentrations in the overlying water and the pore water were approximately proportional to those in the sediment. The conditional partition coefficient between pore water and sediment was 0.9-14$$times$$10$$^{2}$$ L kg$$^{-1}$$, independent of the year of sampling. These results indicated that an equilibrium of $$^{137}$$Cs between pore water and sediment has established in a relatively short period, and $$^{137}$$Cs in the pore water is gradually exported to seawater near the seabed. A simple box model estimation based on these results showed that the $$^{137}$$Cs in the sediment was decreased by about 6% per year by desorption/diffusion of $$^{137}$$Cs from the seabed.

Journal Articles

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

Igarashi, Junya*; Zheng, J.*; Zhang, Z.*; Ninomiya, Kazuhiko*; Satou, Yukihiko; Fukuda, Miho*; Ni, Y.*; Aono, Tatsuo*; Shinohara, Atsushi*

Scientific Reports (Internet), 9(1), p.11807_1 - 11807_10, 2019/08

 Times Cited Count:19 Percentile:66.01(Multidisciplinary Sciences)

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 ($$^{239}$$Pu, $$^{240}$$Pu and $$^{241}$$Pu) 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 $$^{239+240}$$Pu and $$^{241}$$Pu were (1.70-7.06)$$times$$10$$^{-5}$$ Bq and (4.10-8.10)$$times$$10$$^{-3}$$ Bq, respectively and atom ratios of $$^{240}$$Pu/$$^{239}$$Pu and $$^{241}$$Pu/$$^{239}$$Pu 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.

Journal Articles

Factors controlling $$^{134}$$Cs activity concentrations in sediment collected off the coast of Fukushima Prefecture in 2013-2015

Fukuda, Miho*; Aono, Tatsuo*; Yamazaki, Shinnosuke*; Ishimaru, Takashi*; Kanda, Jota*; Nishikawa, Jun*; Otosaka, Shigeyoshi

Geochemical Journal, 52(2), p.201 - 209, 2018/00

 Times Cited Count:3 Percentile:16.86(Geochemistry & Geophysics)

To elucidate recent activity levels and the behavior of radiocesium in the coast off Fukushima Prefecture, lateral and vertical distributions of $$^{134}$$Cs in sediment were observed in 2013-2015 at 12 monitoring stations. At stations around the water depth of 100 m, relatively higher $$^{134}$$Cs activities were observed from surface sedimentary layer (0-3 cm). In these stations, sediments had high content of silt to clay particles and organic matter. The high $$^{134}$$Cs activities in the surface sediments were attributed to accumulation of highly mobile sediment particles. In October 2014, at some coastal stations, sharp peaks of $$^{134}$$Cs activities were observed in the subsurface (5-16 cm) sediments, whereas such broad peaks were not found in October 2015. These results suggest that the $$^{134}$$Cs activities in sediment had largely changed by lateral transport and re-sedimentation on the surface, as well as sediment mixing in the middle-layers.

Journal Articles

Dissolved radiocaesium in seawater off the coast of Fukushima during 2013-2015

Fukuda, Miho*; Aono, Tatsuo*; Yamazaki, Shinnosuke*; Nishikawa, Jun*; Otosaka, Shigeyoshi; Ishimaru, Takashi*; Kanda, Jota*

Journal of Radioanalytical and Nuclear Chemistry, 311(2), p.1479 - 1484, 2017/02

 Times Cited Count:5 Percentile:44.94(Chemistry, Analytical)

In order to investigate processes affecting distribution of radiocaesium in seawater in the adjacent region of Fukushima Daiichi Nuclear Power Plant (FDNPP), relationships between $$^{137}$$Cs activity in seawater and physical properties of seawater (salinity, temperature, and potential density) were observed in seven stations within 10 km radius from the FDNPP. As a whole, $$^{137}$$Cs concentrations in seawater were higher in the vicinity of the FDNPP, and were negatively correlated with potential density. From these results, it can be considered that river water discharge or export of seawater from the FDNPP's harbor has affected the higher activity levels of $$^{137}$$Cs in seawater. It was also observed that the $$^{137}$$Cs-elevated seawater can be advected to the 20$$sim$$50 m depths.

Journal Articles

Recent progress in the energy recovery linac project in Japan

Sakanaka, Shogo*; Akemoto, Mitsuo*; Aoto, Tomohiro*; Arakawa, Dai*; Asaoka, Seiji*; Enomoto, Atsushi*; Fukuda, Shigeki*; Furukawa, Kazuro*; Furuya, Takaaki*; Haga, Kaiichi*; et al.

Proceedings of 1st International Particle Accelerator Conference (IPAC '10) (Internet), p.2338 - 2340, 2010/05

Future synchrotron light source using a 5-GeV energy recovery linac (ERL) is under proposal by our Japanese collaboration team, and we are conducting R&D efforts for that. We are developing high-brightness DC photocathode guns, two types of cryomodules for both injector and main superconducting (SC) linacs, and 1.3 GHz high CW-power RF sources. We are also constructing the Compact ERL (cERL) for demonstrating the recirculation of low-emittance, high-current beams using above-mentioned critical technologies.

Journal Articles

Progress in R&D efforts on the energy recovery linac in Japan

Sakanaka, Shogo*; Ago, Tomonori*; Enomoto, Atsushi*; Fukuda, Shigeki*; Furukawa, Kazuro*; Furuya, Takaaki*; Haga, Kaiichi*; Harada, Kentaro*; Hiramatsu, Shigenori*; Honda, Toru*; et al.

Proceedings of 11th European Particle Accelerator Conference (EPAC '08) (CD-ROM), p.205 - 207, 2008/06

Future synchrotron light sources based on the energy-recovery linacs (ERLs) are expected to be capable of producing super-brilliant and/or ultra-short pulses of synchrotron radiation. Our Japanese collaboration team is making efforts for realizing an ERL-based hard X-ray source. We report recent progress in our R&D efforts.

Oral presentation

Behavior of radiocesium at sediment-water interface off Fukushima

Otosaka, Shigeyoshi; Fukuda, Miho*; Aono, Tatsuo*

no journal, , 

Behavior of dissolved radiocesium near the seafloor is discussed from the distributions of $$^{137}$$Cs in overlying water (seawater collected from $$sim$$30 cm above the seabed) at 14 stations and in pore water at 3 stations off Fukushima (1$$sim$$70 km from Fukushima Daiichi Nuclear Power Plant). The $$^{137}$$Cs concentrations in overlying water, collected during 2015 and 2016, ranged between 5 and 283 mBq/L. The $$^{137}$$Cs concentrations in overlying water were 2$$sim$$3 times higher than those in seawater collected from intermediate (5 m above the bottom) layers. The $$^{137}$$Cs concentrations in pore water were 10$$sim$$30 times higher than those in overlying water. We can consider that radiocesium is dissolved in the overlying water and has been diffused from the seabed through the porewater. Nevertheless, it was estimated that the amount of $$^{137}$$Cs transferred from porewater to benthic organisms does not lead to $$^{137}$$Cs activities exceeding the regulation limits at most stations.

Oral presentation

Exchange of radiocesium between sediment and pore water in the coastal seabed off Fukushima

Otosaka, Shigeyoshi; Fukuda, Miho*; Aono, Tatsuo*

no journal, , 

Behavior of dissolved radiocesium near the seafloor is discussed from the distributions of $$^{137}$$Cs in seawater, seabed sediment and pore water collected from the area around Fukushima. The $$^{137}$$Cs concentrations in the pore water, collected from 2015 to 2017, ranged between 33 and 1186 mBq/L, and were 10$$sim$$40 times higher than those in seawater on the sediment surface. The $$^{137}$$Cs concentration in the overlying water did not show clear differences regardless of the pore size of the filter used for filtration. From these results, it was confirmed that radiocesium in the seabed sediment was dissolved in pore water and diffused to the benthic layer. The apparent distribution coefficient between pore water and sediment was [0.9$$sim$$4.2]$$times$$10$$^{2}$$ L/kg, with no difference depending on the year of sampling. These results indicated that an equilibrium of $$^{137}$$Cs between pore water and sediment has established during the observation period.

Oral presentation

Identification of plutonium isotopes in insoluble particles released by the accident of Fukushima Daiichi Nuclear Power Plant

Igarashi, Junya*; Zheng, J.*; Zhang, Z.*; Ninomiya, Kazuhiko*; Satou, Yukihiko; Fukuda, Miho*; Ni, Y.*; Aono, Tatsuo*; Shinohara, Atsushi*

no journal, , 

Plutonium is one of the most notable radionuclides in the nuclear accident. The amounts of Pu released by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident were investigated so far. However, the existence of Pu isotopes from the global fallout makes it difficult to accurately assessment of Pu contamination by the FDNPP accident. To avoid this problem, identification of Pu contamination source from the Pu isotopic ratios is important. However, various ratios have been reported by the researches due to the contamination from global fallout. In this work, we focused on the insoluble radioactive Cs particles made of mainly SiO$$_{2}$$ (insoluble particles) released from the FDNPP to determine accurate Pu isotopic ratios. Due to its insolubility, the particles retained the original property at the time of emission from the reactor. Therefore, the insoluble particles are considered to be free from the contamination of global fallout. In addition, the amounts of Pu in the insoluble particles provide the information about their formation process in the reactor. In this study, we identified Pu isotopes in insoluble particles by radioactive analysis and ICP-MS measurement. The isotopic ratios of $$^{240}$$Pu/$$^{239}$$Pu and $$^{241}$$Pu/$$^{239}$$Pu were determined as 0.330-0.415 and 0.162-0.178, respectively and activity ratio of $$^{239+240}$$Pu/$$^{137}$$Cs was about 10$$^{-8}$$ in each particle.

Oral presentation

Status and future of radiocesium in the seafloor off Fukushima

Otosaka, Shigeyoshi*; Aono, Tatsuo*; Fukuda, Miho*; Kambayashi, Shota*; Misono, Toshiharu; Dohi, Terumi; Tsuruta, Tadahiko; Suzuki, Takashi; Takahashi, Yoshio*; Sugihara, Naoko*; et al.

no journal, , 

While the amount of cesium-137 ($$^{137}$$Cs: half-life 30.1 years) accumulated on the seabed due to the accident of the Fukushima Daiichi Nuclear Power Plant (0.1-0.2 PBq) is only about 1 to 2% of the total amount of $$^{137}$$Cs transported to the ocean, it has been reported that it will remain for a long time in the coastal areas. On the other hand, long-term migration process of the sedimentary radiocesium and the impact on the ecosystem near the seafloor remain unknown. In this presentation, we will give an overview of the distribution and behavior of $$^{137}$$Cs, especially on the seafloor along the coast of Fukushima, and report the latest results on the processes I the seafloor that should be considered on decadal timescale.

Oral presentation

Variation of radiocaesium in seawater and sediment around off Fukushima

Aono, Tatsuo*; Nishikawa, Jun*; Otosaka, Shigeyoshi*; Takata, Hyoe*; Misono, Toshiharu; Nakanishi, Takahiro; Miura, Hikaru*; Kambayashi, Shota*; Fukuda, Miho*; Sakurada, Masanobu*; et al.

no journal, , 

From 2016 to 2020, the Tohoku Marine Ecosystem Research Vessel Shinsei-maru conducted four research cruises on the dynamics and bioavailability of radionuclides around off Fukushima. Seawater, sediments and organisms were collected mainly around off the Fukushima Daiichi Nuclear Power Plant (FDNPS). The purpose of those cruises is to observe the flux of radionuclides released into the ocean by the FDNPS accident and to understand the bioavailability of radionuclides. In order to understand the contaminated levels of the marine environment, the concentration of radioactive cesium (Cs) in seawater and sediments around off Fukushima was investigated. As a result, the concentration range of dissolved Cs-137 in the surface seawater near the FDNPS from 2016 to 2018 was 10-23 mBq/L, but decreased to 7 mBq/L in 2020. In terms of points, the concentrations of dissolved Cs-137 tended to decrease with time. On the other hand, in sediments, the Cs-137 concentrations were higher in the surface layer (0-2 cm) than the deep layer from 2016 to 2017 and tended to decrease with depth, but after 2018, subsurface vertical maximum of Cs-137 concentrations was observed at some stations. Although these concentrations tended to increase in the subsurface layer, the concentrations in the sediment also tended to decrease with time. In this presentation, we report on the concentration variation of Cs-137 and their characteristics in seawater and sediments around off Fukushima.

Oral presentation

Variation of radiocesium concentration in the marine environment off the coast of Fukushima

Aono, Tatsuo*; Nishikawa, Jun*; Otosaka, Shigeyoshi*; Takata, Hyoe*; Misono, Toshiharu; Nakanishi, Takahiro; Miura, Hikaru*; Fukuda, Miho*; Kambayashi, Shota*; Sakurada, Masanobu*; et al.

no journal, , 

From 2016 to 2020, four research voyages were conducted to investigate the dynamics of radioactive materials in the waters around Fukushima. Seawater and sediment samples were collected in the waters off the Fukushima Daiichi Nuclear Power Plant (FDNPS). The concentration of radioactive cesium (Cs) in seawater and sediment off the coast of Fukushima was surveyed to understand the status of the marine environment. As a result, no significant changes were observed in both seawater and sediment from 2016 to 2020.

Oral presentation

Variation of radiocesium concentration in seawater and sediments at FDNPS

Aono, Tatsuo*; Fukuda, Miho*; Sakurada, Masanobu*; Takahashi, Hiroyuki*; Yamazaki, Shinnosuke*; Kambayashi, Shota*; Misono, Toshiharu; Nakanishi, Takahiro; Miura, Hikaru*; Nishikawa, Jun*; et al.

no journal, , 

From 2016 to 2020, R/V Shinsei-maru of JAMSTEC conducted four research cruises on the dynamics and bioavailability of radionuclides around off Fukushima. Seawater, sediments and organisms were collected mainly around off the Fukushima Daiichi Nuclear Power Plant (FDNPS). The purpose of those cruises is to observe the flux of radionuclides released into the ocean by the FDNPS accident and to understand the bioavailability of radionuclides. In order to understand the contaminated levels of the marine environment, the concentration of radiocaesium (Cs) in seawater and sediments around off Fukushima was investigated.

14 (Records 1-14 displayed on this page)
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