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Miura, Hikaru*; Kuribara, Yuichi; Takahashi, Yoshio*
Chikyu Kagaku, 55(4), p.122 - 131, 2021/12
Radiocesium-bearing microparticles (CsMPs), glassy water-resistant particles with highly concentrated radiocesium, were emitted by the Fukushima Daiichi Nuclear Power Plant accident. Since first discovery of CsMPs, a number of studies have analyzed the particles isolated from environmental samples and revealed their physical and chemical properties, distribution, and migration. This paper is intended to provide an overview focusing on the environmental transport and impact of CsMPs. First, we begin by reviewing the relationship between deposition areas and atmospheric plumes of CsMPs found on land. Next, search and separation methods for CsMPs will be described. Then, secondary transport via rivers and effect of CsMPs on Kd values of Cs in rivers will be discussed. Finally, CsMPs found in the ocean and their difference from terrestrial ones will be summarized.
Miura, Hikaru*; Ishimaru, Takashi*; Ito, Yukari*; Kuribara, Yuichi; Otosaka, Shigeyoshi*; Sakaguchi, Aya*; Misumi, Kazuhiro*; Tsumune, Daisuke*; Kubo, Atsushi*; Higaki, Shogo*; et al.
Scientific Reports (Internet), 11, p.5664_1 - 5664_11, 2021/03
Times Cited Count：8 Percentile：64.15(Multidisciplinary Sciences)For the first time, we isolated and investigated seven CsMPs (radioactive caesium-bearing microparticles) from marine particulate matter and sediment. From the elemental composition, the 
Cs/
Cs activity ratio, and the Cs activity per unit volume results, we inferred that the five CsMPs collected from particulate matter were emitted from Unit 2 of the FDNPP, whereas the two CsMPs collected from marine sediment were possibly emitted from Unit 3. The presence of CsMPs can cause overestimation of the solid-water distribution coefficient of Cs in marine sediments and particulate matter and a high apparent radiocaesium concentration factor for marine biota. CsMPs emitted from Unit 2, which were collected from the estuary of a river that flowed through a highly contaminated area, may have been deposited on land and then transported by the river. By contrast, CsMPs emitted from Unit 3 were possibly transported eastward by the wind and deposited directly onto the ocean surface.
Miura, Hikaru*; Kuribara, Yuichi; Yamamoto, Masayoshi*; Sakaguchi, Aya*; Yamaguchi, Noriko*; Sekizawa, Oki*; Nitta, Kiyofumi*; Higaki, Shogo*; Tsumune, Daisuke*; Itai, Takaaki*; et al.
Scientific Reports (Internet), 10, p.11421_1 - 11421_9, 2020/07
Times Cited Count：14 Percentile：69.92(Multidisciplinary Sciences)Igarashi, Yasuhito*; Kogure, Toshihiro*; Kuribara, Yuichi; Miura, Hikaru*; Okumura, Taiga*; Satou, Yukihiko; Takahashi, Yoshio*; Yamaguchi, Noriko*
Journal of Environmental Radioactivity, 205-206, p.101 - 118, 2019/09
Times Cited Count：57 Percentile：73.64(Environmental Sciences)Scientists face challenge in identifying the radioactive materials which are found as dotted images on various imaging plate (IP) autoradiographic photos of radioactively contaminated materials by the Fukushima Dai-ichi Nuclear Power Plant (F1NPP, or FDNPP) accident, such as air filter, fugitive dust, surface soil, agricultural materials, and water-shed samples. It has been revealed that they are minute particles with distinct morphology and elemental composition with high specific radioactivity, and different from those of the so-called Chernobyl hot particles. Basically, they are glassy particles once molten, composed of Si, O, Fe, Zn etc. with highly concentrated radiocaesium, which can be called as radiocaesium-bearing microparticles (CsMP). At present, CsMP can be classified into two types, Types-A and -B, which are characterized by different specific radioactivity, Cs/Cs ratio, size and morphology, and geographic distribution around F1NPP. Such studies on the CsMP from various aspects have provided valuable information about what happened in the nuclear reactors during the F1NPP accident and fates of the CsMP in the environment. This review first provides a retrospective view on the research history of the CsMP, which is helpful to understand the unique character of the CsMP. Subsequently, more details about the current understanding of the natures of these hot particles, such as origin, morphology, chemical compositions, thermal properties, water-solubility, and secondary migration of CsMP in river and ocean systems are described with future prospects.
Kuribara, Yuichi; Yamaguchi, Akiko*; Higaki, Shogo*; Ohara, Yoshiyuki; Takahashi, Yoshio*
no journal, ,
In order to investigate the behavior of radium in the Ningyo-toge Environmental Engineering Center, radium in the core sample in the center was analyzed with HPGe semiconductordetector. As a result, concentrate of radium was observed in the weathered granite in the lower part of the core sample.
Yamaguchi, Akiko; Kuribara, Yuichi; Okumura, Masahiko; Takahashi, Yoshio*
no journal, ,
no abstracts in English
Kuribara, Yuichi; Yamaguchi, Akiko*; Higaki, Shogo*; Ohara, Yoshiyuki; Takahashi, Yoshio*
no journal, ,
In order to investigate the behavior of radium (Ra) in the Ningyo-toge Environmental Engineering Center, 
Ra/
U activity ratio in two boring core samples in the center was analyzed with HPGe semiconductor detector. The Ra/U ratio was below 1 and over 1 in the U enriched and contained clay mineral layers, respectively. Based on the radioactive equilibrium and mass balance calculation, it was suggested that Ra and U eluted to groundwater migrated from the U enriched layer to the contained clay minerals layer when Ra was selectivity fixed on the contained clay mineral layer. EXAFS and micro-XRF-XANES-XRD for Ba, used as an analog of Ra, confirmed that Ba
was adsorbed on clay minerals as IS complex, and Ra was expected to show similar behavior. Therefore, it was indicated that Ra migrated from U concentrated layer was adsorbed and fixed on clay minerals in the environment of the Ningyo-toge Environmental Engineering Center.
Kuribara, Yuichi; Yamaguchi, Akiko; Higaki, Shogo*; Ohara, Yoshiyuki; Takahashi, Yoshio*
no journal, ,
In order to investigate the migration of radium isotopes in the former open-pit mining site of the Ningyo-toge Environmental Engineering Center, the U- and Th-series nuclides including radium isotopes in the boring core samples inside and outside the site were analyzed. Additionally, to clarify the partitions of Ra-226 in the solid phase, sequential extraction experiments were conducted on the Ningyo-Toge layer and the weathered granite layer. As aresult, it was estimated that the radium isotopes were migrated from the Ningyo-Toge layer to the weathered granite layer below it.
Miura, Hikaru*; Kuribara, Yuichi; Yamamoto, Masayoshi*; Sakaguchi, Aya*; Higaki, Shogo*; Takahashi, Yoshio*
no journal, ,
A synchrotron radiation X-ray analysis was performed on radioactive particles released into the environment due to the Fukushima Dai-ichi Nuclear Power Plant accident, uranium particles (4 valence and 6 valence) with a size of several microns were present in the particles from the Unit 1. Since these uranium particles also contain zirconium, which is considered to be derived from the fuel cladding, it was presumed that the eutectic mixture of the fuel in the reactor and its cladding was incorporated into the radioactive particulates and released into the environment.
Yamaguchi, Akiko; Kuribara, Yuichi; Higaki, Shogo*; Okumura, Masahiko; Takahashi, Yoshio*
no journal, ,
no abstracts in English
