Tachi, Yukio; Sato, Tomofumi*; Akagi, Yosuke*; Kawamura, Makoto*; Nakane, Hideji*; Terashima, Motoki; Fujiwara, Kenso; Iijima, Kazuki
Science of the Total Environment, 724, p.138098_1 - 138098_11, 2020/07
To understand and predict radiocesium transport behaviors in the environment, highly contaminated sediments from Ukedo and Odaka rivers around the Fukushima Daiichi Nuclear Power Plant were investigated systematically focusing on key factors controlling radiocesium sorption and fixation, including particle size, clay mineralogy and organic matter.
Tachi, Yukio; Sato, Tomofumi*; Takeda, Chizuko*; Ishidera, Takamitsu; Fujiwara, Kenso; Iijima, Kazuki
Science of the Total Environment, 724, p.138097_1 - 138097_10, 2020/07
To understand and predict radiocesium transport behaviors in the environment, sorption and fixation behaviors of radiocesium on river sediments from Ukedo and Odaka rivers around the Fukushima Daiichi Nuclear Power Plant were investigated systematically focusing on Cs sorption and fixation mechanisms and their relationship with Cs concentrations and sediment properties including clay mineralogy and organic matter.
Yin, X.; Zhang, L.*; Meng, C.*; Inaba, Yusuke*; Wang, X.*; Nitta, Ayako; Koma, Yoshikazu; Takeshita, Kenji*
Journal of Hazardous Materials, 387, p.121677_1 - 121677_10, 2020/04
Sugiura, Yuki; Suyama, Tadahiro*; Tachi, Yukio
JAEA-Data/Code 2019-022, 40 Pages, 2020/03
Sorption behavior of radionuclides (RNs) in buffer materials, rocks and cementitious materials is one of the key processes in a safe geological disposal. This report focuses on updating of JAEA sorption database (JAEA-SDB) as a basis of integrated approach for the performance assessment (PA)-related distribution coefficient (K) setting and development of mechanistic sorption models. K data and their quality assurance (QA) results were updated by focusing on the following systems as potential needs extracted from our recent activities on the K setting and development of mechanistic models, i.e., clay minerals, sedimentary rocks and cementitious materials. As a result, 6,702 K data from 60 references were added and the total number of K values in JAEA-SDB reached 69,679. The QA/classified K data reached about 72% for all K data in JAEA-SDB.
Collaborative Laboratories for Advanced Decommissioning Science; Osaka University*
JAEA-Review 2019-029, 36 Pages, 2020/02
JAEA/CLADS, had been conducting the Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development (hereafter referred to "the Project") in FY2018. The Project aims to contribute to solving problems in nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2018, this report summarizes the research results of the "Development of Gel Filler that Facilitates Fuel Debris Retrieval". When gel materials such as polymer, silicate and clay minerals with adjusted viscosity are used in the process of debris retrieval, the gel would not leak down from the damaged parts, resulting in the reduction of surrounding air dose rate. In addition, gel materials can reduce the diffusion and scattering of dust that is produced by cutting. For these reasons, we propose a method where inside of a containment vessel is filled by gel materials in order to simplify the debris retrieval.
Sasamoto, Hiroshi; Sato, Hisao*; Arthur, R. C.*
Journal of Geochemical Exploration, 188, p.318 - 325, 2018/05
Ammonium is potentially an important constituent of deep groundwater under reducing condition. The retention of cesium by sorption in geological formations may have an important role ensuring the long-term safety of high-level radioactive waste. Cesium sorption will be affected by competing effects due to dissolve cation likely ammonium in groundwater, however. In the present study, a possible reaction to control of ammonium in deep groundwater was evaluated based on the data selected in the Horonobe as a test case in Japan. Results of investigation of mineralogy, thermodynamic evaluation of groundwaters and the Electron Probe Micro Analysis (EPMA) to identify nitrogen distribution on minerals suggest that the clay minerals bearing potassium, particularly smectite, illite and interstratified illite/smectite, appear to control the ammonium concentration in groundwaters by ion exchange reactions. Additionally, the selected groundwaters in the Horonobe seem to resemble to the gas and oil fields groundwater in the screened dataset in Japan in terms of ammonium distribution.
Nihon Genshiryoku Gakkai-Shi ATOMO, 59(8), p.441 - 443, 2017/08
no abstracts in English
Hirao, Norie; Shimoyama, Iwao; Baba, Yuji; Izumi, Toshinori; Okamoto, Yoshihiro; Yaita, Tsuyoshi; Suzuki, Shinichi
Bunseki Kagaku, 65(5), p.259 - 266, 2016/05
After the Fukushima nuclear plant accident, radiocesium was strongly fixed to clay minerals in the soil. Some dry methods with heating are being developed to remove radiocesium from the soil. In this work, we propose a new dry method that combines heat treatment in vacuum and molten salts to reduce the processing temperature in dry methods. Vermiculite saturated with non-radioactive Cs was heated in vacuum, and Cs contents in the vermiculite were compared before and after heating using X-ray photoelectron spectroscopy. Approximately 40% of cesium were removed by heating at 800C for three minutes when only vermiculite was heated. Approximately 70% of cesium were removed by heating at 450C for three minutes when vermiculite was heated with NaCl/CaCl mixed salts. Based on these results, this method is expected to reduce temperature and increase efficiency on dry methods for cesium removal from clay minerals.
Ikeda, Takashi; Suzuki, Shinichi; Yaita, Tsuyoshi
Journal of Physical Chemistry A, 119(30), p.8369 - 8375, 2015/07
Adsorption states of alkali metal ions in three kinds of 2:1 type clay minerals are systematically investigated via first-principles-based metadynamics. Our reconstructed free energy surfaces in a two dimensional space of coordination numbers specifically employed as collective variables for describing the interlayer cations show that an inner-sphere (IS) complex is preferentially formed for Cs in the 2:1 type trioctahedral clay minerals with saponitelike compositions, where lighter alkali ions show a tendency to form an outer-sphere one instead. The strong preference for an IS complex observed for Cs is found to result partially from the capability of recognizing selectively Cs ions at basal O atoms with the Lewis basicity significantly enhanced by the isomorphic substitution in tetrahedral sheets.
Yamada, Hirohisa*; Yokoyama, Shingo*; Watanabe, Yujiro*; Suzuki, Masaya*; Suzuki, Shinichi; Hatta, Tamao*
Nihon Ion Kokan Gakkai-Shi, 25(4), p.207 - 211, 2014/11
no journal, ,
no abstracts in English
no journal, ,
no abstracts in English
Yin, X.; Koma, Yoshikazu; Inaba, Yusuke*; Takeshita, Kenji*
no journal, ,
Hu, Q.*; Wang, Q.*; Zhao, C.*; Tachi, Yukio; Fukatsu, Yuta
no journal, ,
A low aqueous-phase diffusion in low-permeable clay barrier materials has been accepted as a critical process in the long-term performance evaluation of nuclear waste repository. Low-permeable clay materials whose pores are poorly interconnected are known to have anomalous diffusion properties that strongly impact long-term net diffusion. Related research works with mudrocks of Wakkanai formation of Horonobe URL in Japan, Opalinus clay of Mt. Terri URL in Switzerland, as well as various shale and clay mineral, utilizes a complementary suite of pore structure characterization approaches (e.g., mercury intrusion porosimetry, small angle neutron scattering) and tracer experiments followed with micro-scale mapping with laser ablation-ICP-MS. These results presents the relationship between pore connectivity and anomalous diffusion in clay materials. Pore size is not the major contributor to slow fluid flow and radionuclide transport, the anomalous behavior appears to be caused by low pore connectivity.