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Otosaka, Shigeyoshi; Kobayashi, Takuya; Machida, Masahiko
Nihon Genshiryoku Gakkai-Shi ATOMO
, 59(11), p.659 - 663, 2017/11
It is estimated that about 70% of radiocesium released to the environment by the Fukushima Daiichi nuclear accident was carried to the ocean. In addition to monitoring surveys by the government, oceanographic research by many institutions has revealed the distribution and behavior of the accident-derived radiocesium in the ocean. Numerical simulations are efficiently used in such oceanographic investigations, and further improvements are being made based on findings newly obtained after the accident. In this paper, we review the abundance and behavior of radiocesium in the coastal area of Fukushima, deepen the scientific understanding of the current situation of environmental restoration, and explain the issues to be addressed in the future.
Nagao, Seiya*; Otosaka, Shigeyoshi; Kaeriyama, Hideki*
Journal of Oceanography, 73(5), P. 527, 2017/10
Times Cited Count：1 Percentile：46.07(Oceanography)More than five years have passed since the accident at the Fukushima Daiichi Nuclear Power Plant, and many investigations have been carried out in the marine environment. Regarding the radiocesium concentration in seabed sediment, from May 2011, monitoring survey is continuing mainly in the coastal areas of Miyagi, Fukushima, Ibaraki and Chiba prefectures. However, due to its heterogeneity, the difficulty of observation, etc., the assessment of the influence of the accident-derived radionuclides on seabed sediments and the benthic ecosystem is delayed compared to other environmental investigations. As the Guest Editors, the authors set up a special section in "Journal of Oceanography", including four papers arguing about factors affecting the temporal change of the radiocesium concentrations in estuarine, coastal and offshore sediments. This preface shows the planning intention of the special issue, and also outlines the contents.
Yamamoto, Masahiro
Zairyo To Kankyo, 66(1), p.3 - 12, 2017/01
The laboratory simulation tests which could be reproduced the corrosion reactions propagating in the actual environments were utilized to analyze the mechanism of corrosion phenomena. In this report, some results are introduced in the cases of maritime structures and nuclear facilities. Experimental apparatus was originally designed to obtain the data in high radioactive condition simulating actual plants. One is a result showing the effect of Np ion to the corrosion of stainless steel in nuclear fuel reprocessing plant. Corrosion mechanism was revealed that Np
ion is reduced to Np
ion by a corrosion reaction of stainless steel and then re-oxidized to Np ion in the bulk solution. And repetition of this cycle accelerated corrosion of stainless steel by a little amounts of Np addition in nitric acid solution. Another result is introduced that an effect of H
O created by radiolysis of cooling water at high radioactive environment in light water reactor.
Kobayashi, Takuya; Togawa, Orihiko
Kaiyo Deta Doka Semina 2003, p.59 - 64, 2003/08
no abstracts in English
Muromura, Tadasumi
Hoken Butsuri, 34(2), p.216 - 217, 1999/06
no abstracts in English
; ; Isozaki, Tokuju; ; ; *
PNC TN8440 97-037, 501 Pages, 1997/10
None
*; Kishimoto, Yoichiro; Narita, Osamu; Shinohara, Kunihiko*
PNC TN841 77-55, 83 Pages, 1977/08
no abstracts in English
Otosaka, Shigeyoshi; Sato, Yuhi; Suzuki, Takashi; Kuwabara, Jun
no journal, ,
Transport processes of biohilic radionuclides, derived from the accident of Fukushima Daiichi Nuclear Power Plant, are discussed from distribution of 
I in seabed sediment off Fukushima. Concentrations of I in the seabed sediment in 2011 ranged between 0.02 and 0.45 mBq/kg, and were generally higher in the coastal region. In January 2013, about two years after the accident, concentrations of I in the sediment surface slightly increased in the shelf-edge region (bottom depth: 200
400 m), and such a trend was not observed for radiocesium. The preferential accumulation of I in the shelf-edge sediment was explained by lateral transport of sedimentary I from the coastal to shelf-edge regions. Considering the geochemical characteristics of iodine, it can be considered that particulate organic matter near the seabed efficiently carried I to the offshore.
Jeon, H.; Otosaka, Shigeyoshi; Yamashita, Yohei*; Ogawa, Hiroshi*
no journal, ,
Measurements of the radiocarbon content of marine dissolved organic carbon (DO
C) broadened our perspective on the role of DOC in the marine carbon cycle. However fewer measurements have been performed because of methodological difficulties associated with low concentration of DOC and an overwhelming proportion of salts. In order to collect enough DOC for radiocarbon analysis, UV oxidation is one of the most commonly used methods by irradiating seawater samples with ultraviolet light. Unlike other studies where medium pressure mercury arc UV lamp are used, this study attempts to improve the system with two grid lamps in order to reduce the demand for high electric power installation and to miniaturize the instrument for easier handling. We aim to verify the performance of improved equipment by processing C reference materials as well as seawater samples.
Otosaka, Shigeyoshi; Fukuda, Miho*; Aono, Tatsuo*
no journal, ,
Behavior of dissolved radiocesium near the seafloor is discussed from the distributions of 
Cs in seawater, seabed sediment and pore water collected from the area around Fukushima. The Cs concentrations in the pore water, collected from 2015 to 2017, ranged between 33 and 1186 mBq/L, and were 1040 times higher than those in seawater on the sediment surface. The 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 [0.94.2]
10
L/kg, with no difference depending on the year of sampling. These results indicated that an equilibrium of Cs between pore water and sediment has established during the observation period.
