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Sr (
Sr) from port of Fukushima Daiichi Nuclear Power Plant; Analysis of the temporal variation from the accident to March 2022 and evaluation of its impact on Fukushima coast and offshore areasMachida, Masahiko; Iwata, Ayako; Yamada, Susumu; Otosaka, Shigeyoshi*; Kobayashi, Takuya; Funasaka, Hideyuki*; Morita, Takami*
Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 22(4), p.119 - 139, 2023/11
We estimate monthly discharged inventory of Sr from port of Fukushima Daiichi Nuclear Power Plant (1F) from Jun. 2013 to Mar. 2022 by using the Voronoi tessellation method inside the port, following the monitoring of Sr sea water radioactivity concentration inside the port. The results suggest that the closure of sea side impermeable wall is the most effective for the reduction of discharged one. In addition, the results roughly reveal the monthly discharged inventory required to observe visible enhancement of the sea radioactivity concentration from the background level in each area. Such outcome is significant for considering environmental impacts on the planned future releasing of the treated water accumulated in 1F site.
Machida, Masahiko; Iwata, Ayako; Yamada, Susumu; Otosaka, Shigeyoshi*; Kobayashi, Takuya; Funasaka, Hideyuki*; Morita, Takami*
Journal of Nuclear Science and Technology, 60(3), p.258 - 276, 2023/03
Times Cited Count：1 Percentile：31.61(Nuclear Science & Technology)We estimate monthly discharge inventory of tritium from the port of Fukushima Dai-ichi Nuclear Power Plant (1F) from Jun. 2013 to Mar. 2020 using the Voronoi tessellation scheme, following the tritium monitoring results inside the port started in Jun. 2013. As for the missing period from the first month of 1F accident, Apr. 2011 to May 2013, we calculate the tritium discharge inventory by utilizing the concentration ratio of tritium to 
Cs in stagnant contaminant water during the initial direct run-off period until Jun. 2011 and the discharge inventory correlation between tritium and Cs for the next-unknown continuous-discharge period from Jul. 2011 to May 2013. From all the estimated results over 9 years, we find that the monthly discharge inventory sharply dropped immediately after closing the seaside impermeable wall in Oct. 2015 and consequently coincided well with the sum of input inventories of drainage water and subdrain etc. purified water into the port. By comparing the above estimated results with those in the normal operation period before the accident, we point out that the discharge inventory from 1F port after the accident is not so large. Even the estimation value for the accident year 2011 is found to be comparable to the maximum of operating pressurized water reactors releasing relatively large inventories in the order. At the national level, the total domestic release inventory in Japan significantly decreased after the accident owing to the operational shutdown of most plants. Furthermore, the total Japanese discharge inventory including 1F are found to be minor compared with those of nuclear reprocessing plants and heavy-water reactors on a worldwide level. From the above results, we suggest that various scenarios can be openly discussed regarding the management of tritium stored inside 1F with the help of the present estimated data and its comparison with the past discharge inventory as well as those of other nuclear facilities.
Machida, Masahiko; Iwata, Ayako; Yamada, Susumu; Otosaka, Shigeyoshi*; Kobayashi, Takuya; Funasaka, Hideyuki*; Morita, Takami*
Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 22(1), p.12 - 24, 2023/01
We estimate inventory of tritium in two sea areas corresponding to coastal and offshore ones around Fukushima Daiichi Nuclear Power Plant (1F) based on the measurement results of sea-water tritium concentration monitored constantly from 2013 to Jan. 2021 by using Voronoi tessellation scheme. The obtained results show that the offshore area inventory and its temporal variation amount correspond to approximately 1/5 and 1/40 of that of the treated-water accumulated inside 1F, respectively. These results just suggest that the presence of tritium already included in sea-water as the background is non negligible in evaluating the environmental impact by releasing the accumulated treated-water into the sea region. We also estimate the offshore area inventory before 1F accident and find that it had exceeded over 1F stored inventory over about 30 years from 1960s to 1980s with approximately 4 times larger in the peak decade, 1960s. This fact means that we had already experienced more contaminated situation over 30 years in the past compared to the conservative case appeared by just releasing whole the present 1F inventory. Here, it should be also emphasized that the past contaminated situation was shared by the entire world. We further extend the estimation region into a wider region including an offshore area from Miyagi to Chiba prefectures and find that the area average inventory is now comparable to a half of the present 1F one. Finally, we estimate internal dose per year via ingesting fishes caught inside the area when 1F inventory is just added inside the area and kept for a year. The result indicates that it approximately corresponds to 1.0
of the dose from natural radiation sources. From these estimation results, it is found that all the tritium inventory stored inside 1F never contribute to significant dose increment even when it is instantly released into the area.
Machida, Masahiko; Iwata, Ayako; Yamada, Susumu; Otosaka, Shigeyoshi*; Kobayashi, Takuya; Funasaka, Hideyuki*; Morita, Takami*
Nihon Genshiryoku Gakkai Wabun Rombunshi, 21(1), p.33 - 49, 2022/03
We estimate monthly discharge inventory of tritium from the port of Fukushima Daiichi Nuclear Power Plant (1F) from Jun 2013 to Mar 2020 by using the Voronoi tessellation scheme, following that the tritium monitoring inside the port has started since Jun 2013. As for the missing period from the initial month, Apr 2011 to May 2013, we calculate it by utilizing the concentration ratio of tritium to that of Cs in stagnant contaminant water during the initial direct discharged period to Jun 2011 and the discharge inventory correlation between tritium and Cs for the next-unknown continuously-discharged period up to May 2013. From the all- estimated results over 9 years, we find that the monthly discharge inventory sharply dropped just after closing the sea-side impermeable sea-wall in Oct. 2015 and subsequently coincided well with the sum of those of drainage and subdrain. By comparing the estimated results with those in the normal operation period before the accident, we point out that the discharge inventory from 1F port is not so large compared to those during the normal operation. Even the estimated one in year 2011 is found to be comparable to the maximum of operating pressurized water reactors discharging relatively large inventory in the order. In the nation level, the whole Japan domestic discharge inventory significantly decreased after the accident due to operation shutdown of most plants. Furthermore, 1F and even Japanese total discharge inventory are found to be entirely minor when comparing those of nuclear reprocessing plants and heavy-water reactors in world-wide level. From the above, we suggest that various scenarios can be openly discussed on the management in tritium stored inside 1F with help of the present estimated data and its comparison with the past discharge inventory.
Machida, Masahiko; Yamada, Susumu; Iwata, Ayako; Otosaka, Shigeyoshi; Kobayashi, Takuya; Watanabe, Masahisa; Funasaka, Hideyuki; Morita, Takami*
Journal of Nuclear Science and Technology, 57(8), p.939 - 950, 2020/08
Times Cited Count：9 Percentile：71.58(Nuclear Science & Technology)After direct discharges of highly contaminated water of the Fukushima Daiichi Nuclear Power Plant (1F) from April to May 2011, Kanda suggested that relatively small amounts of run-off of radionuclides from the 1F port into the Fukushima coastal region subsequently continued by his estimation method. However, the estimation period was limited to up to September 2012. Therefore, this paper estimates the discharge inventory up to June 2018. In the missing period, the Japanese government and Tokyo Electric Power Company Holdings have continued efforts to stop the discharge, and consequently, the radionuclide concentration in seawater inside the 1F port has gradually diminished. We show the monthly discharge inventory of Cs up to June 2018 by two methods, i.e., Kanda method partially improved by the authors and a more sophisticated method using Voronoi tessellation reflecting the increase in the number of monitoring points inside the 1 F port. The results show that the former always yields overestimated results compared with the latter, but the ratio of the former to the latter is less than one order of magnitude. Using these results, we evaluate the impact of the discharge inventory from the 1F port into the coastal area and radiation dose upon fish ingestion.
Fujihara, Masayoshi*; Morita, Katsuhiro*; Mole, R.*; Mitsuda, Setsuo*; Toyama, Takami*; Yano, Shinichiro*; Yu, D.*; Sota, Shigetoshi*; Kuwai, Tomohiko*; Koda, Akihiro*; et al.
Nature Communications (Internet), 11, p.3429_1 - 3429_7, 2020/07
Times Cited Count：37 Percentile：90.63(Multidisciplinary Sciences)Machida, Masahiko; Yamada, Susumu; Iwata, Ayako; Otosaka, Shigeyoshi; Kobayashi, Takuya; Watanabe, Masahisa; Funasaka, Hideyuki; Morita, Takami*
Nihon Genshiryoku Gakkai Wabun Rombunshi, 18(4), p.226 - 236, 2019/12
After direct discharges of highly-contaminated water from Unit 2 and 3 in Fukushima Daiichi Nuclear Power Plant (1F) in April to May 2011, Kanda suggested that relatively small run-off of radionuclides from 1F port into Fukushima coastal region has subsequently continued by using his estimation scheme. However, the estimation period was limited until September 2012, and there has been no report on the issue since the work. Therefore, this paper focuses on discharge inventory from 1F port until June 2018. In the missing period, the central government and Tokyo Electric Power Company Holdings have done continuous efforts to stop the discharge, and consequently sea water concentration inside 1F port has diminished gradually. We show monthly discharge inventory of Cs-137 until June 2018 by two schemes, i.e., Kanda's scheme partially improved by authors and more sophisticated one using Voronoi tessellation reflecting the increment of the number of monitoring points inside 1F port. The results show that the former always presents overestimated results compared to the latter but the ratio of former to latter is less than one order. Based on these results, we evaluate impact of discharge inventory from 1F port into the coastal area and radiation does via fish digestion.
= 100 with a multireflection time-of-flight mass spectrographIto, Yuta*; Schury, P.*; Wada, Michiharu*; Arai, Fumiya*; Haba, Hiromitsu*; Hirayama, Yoshikazu*; Ishizawa, Satoshi*; Kaji, Daiya*; Kimura, Sota*; Koura, Hiroyuki; et al.
Physical Review Letters, 120(15), p.152501_1 - 152501_6, 2018/04
Times Cited Count：60 Percentile：93.36(Physics, Multidisciplinary)Masses of 
Es, 
Fm and the transfermium nuclei 
Md, and 
No, produced by hot- and cold-fusion reactions, in the vicinity of the deformed 
neutron shell closure, have been directly measured using a multi-reflection time-of-flight mass spectrograph. The masses of Es and 
Md were measured for the first time. Using the masses of 
Md as anchor points for 
decay chains, the masses of heavier nuclei, up to 
Bh and 
Mt, were determined. These new masses were compared with theoretical global mass models and demonstrated to be in good agreement with macroscopic-microscopic models in this region. The empirical shell gap parameter 
derived from three isotopic masses was updated with the new masses and corroborate the existence of the deformed neutron shell closure for Md and Lr.
Schury, P.*; Wada, Michiharu*; Ito, Yuta*; Kaji, Daiya*; Haba, Hiromitsu*; Hirayama, Yoshikazu*; Kimura, Sota*; Koura, Hiroyuki; MacCormick, M.*; Miyatake, Hiroari*; et al.
Nuclear Instruments and Methods in Physics Research B, 407, p.160 - 165, 2017/06
Times Cited Count：14 Percentile：78.05(Instruments & Instrumentation)Various isotopes of Ac, Ra, Fr, and Rn were produced by fusion-evaporation reactions using a 
Ca beam. The energetic ions were stopped in and extracted from a helium gas cell. The extracted ions were identified using a multi-reflection time-of-fight mass spectrograph. In all cases, it was observed that the predominant charge state for the extracted ions, including the alkali Fr, was 2+.
Schury, P.*; Wada, Michiharu*; Ito, Yuta*; Kaji, Daiya*; Arai, Fumiya*; MacCormick, M.*; Murray, I.*; Haba, Hiromitsu*; Jeong, S.*; Kimura, Sota*; et al.
Physical Review C, 95(1), p.011305_1 - 011305_6, 2017/01
Times Cited Count：48 Percentile：96.07(Physics, Nuclear)Using a multireflection time-of-flight mass spectrograph located after a gas cell coupled with the gas-filled recoil ion separator GARIS-II, the masses of several -decaying heavy nuclei were directly and precisely measured. The nuclei were produced via fusion-evaporation reactions and separated from projectilelike and targetlike particles using GARIS-II before being stopped in a helium-filled gas cell. Time-of-flight spectra for three isobar chains, 
Fr-Rn-At-Po, 
Fr- Rn-At-Po-Bi, and 
Fr-Rn-At, were observed. Precision atomic mass values were determined for 
Fr, 
Rn, and At. Identifications of Bi, Po, Rn, and At were made with N
10 detected ions, representing the next step toward use of mass spectrometry to identify exceedingly low-yield species such as superheavy element ions.
Schury, P. H.*; Wada, Michiharu*; Ito, Yuta*; Naimi, S.*; Sonoda, Tetsu*; Mita, Koki*; Takamine, Aiko*; Okada, Kunihiro*; Wollnik, H.*; Chon, S.*; et al.
Nuclear Instruments and Methods in Physics Research B, 317(Part B), p.537 - 543, 2013/12
Times Cited Count：28 Percentile：89.14(Instruments & Instrumentation)A multi-reflection time-of-flight (MRTOF) mass spectrograph has been implemented at RIKEN to provide high-precision mass measurements of very short-lived nuclei. Of particular interest are mass measurements of r-process nuclei and trans-uranium nuclei. In such nuclei, the MRTOF can perform on par with or better than traditional Penning trap systems. We demonstrate that the MRTOF-MS is capable of accurately attaining relative mass precision of 
m/m 
10
and describe it's utility with heavy, short-lived nuclei.
Co in the digestive glands of the common octopus, 
, in the East China SeaMorita, Takami*; Otosaka, Shigeyoshi; Fujimoto, Ken*; Nishiuchi, Ko*; Kimoto, Katsunori*; Yamada, Haruya*; Kasai, Hiromi*; Minakawa, Masayuki*; Yoshida, Katsuhiko*
Marine Pollution Bulletin, 60(8), p.1193 - 1199, 2010/08
Times Cited Count：3 Percentile：10.23(Environmental Sciences)Significant concentrations of Co, Cs and 
Ag were detected in common octopus specimens collected in the East China Sea during two periods, 1986-1989 and 1996-2005. The radionuclides detected in the former period were thought to originate from the global fallout. On the other hand, the source of Co in the latter period has remained unclear because the Co concentration decreased continuously with shorter half-lives than the physical half-lives. This tendency suggests that the source of Co in 1996-2005 was identical and was temporary supplied to the East China Sea. Investigations of common octopus in the other area indicated that the origin of the pollutant source of Co in 1996-2005 occurred locally in the restricted area in the East China Sea rather than in the coastal area of Japan.
Morita, Takami*; Niwa, Kentaro*; Fujimoto, Ken*; Kasai, Hiromi*; Yamada, Haruya*; Nishiuchi, Ko*; Sakamoto, Tatsuya*; Godo, Waichiro*; Taino, Seiya*; Hayashi, Yoshihiro*; et al.
Science of the Total Environment, 408(16), p.3443 - 3447, 2010/06
Times Cited Count：13 Percentile：33(Environmental Sciences)Iodine-131 (
I) was detected in brown algae collected off the Japanese coast. The maximum measured specific activity of I in brown algae was 0.37
0.010 Bq/kg-wet. Cesium-137 (Cs) was also detected in all brown algal samples used in this study. There was no correlation between specific activities of I and Cs in these seaweeds. Low specific activity and minimal variability of Cs in brown algae indicated that past nuclear weapon tests were the source of Cs. Although nuclear power facilities are known to be pollution sources of I, there was no relationship between the sites where I was detected and the locations of nuclear power facilities. Most of the sites where I was detected were near big cities with large populations. On the basis of the results, we suggest that the likely pollution source of I, detected in brown seaweeds, is not nuclear power facilities, but nuclear medicine procedures.
Yamada, Susumu; Machida, Masahiko; Iwata, Ayako; Otosaka, Shigeyoshi*; Kobayashi, Takuya; Watanabe, Masahisa; Funasaka, Hideyuki*; Morita, Takami*
no journal, ,
no abstracts in English
