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Sugiura, Yuki; Ishidera, Takamitsu; Aoyagi, Noboru; Mei, H.; Saito, Takumi*; Tachi, Yukio
no journal, ,
Francisco, P. C. M.; Ishidera, Takamitsu; Shiwaku, Hideaki; Kikuchi, Ryosuke*; Tachi, Yukio
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Fukatsu, Yuta; Hu, Q.*; Tachi, Yukio
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Dohi, Terumi; Niizato, Tadafumi; Sasaki, Yoshito; Iijima, Kazuki
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Iijima, Kazuki
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On the way of decommissioning of Fukushima Daiichi Nuclear Power Station (FDNPS), huge amount of various radioactive solid wastes will be generated. Large uncertainties of their characteristics and amount are major obstacles in considering future waste treatment and disposal strategies. In this study, approaches of safety assessment of waste disposal were investigated in order to clarify the required waste properties and optimize the entire waste stream. In case of FDNPS wastes, due to the generic conditions with large uncertainties, too much conservative assumption leads to too robust requirement for disposal system, so that the assessment in the reference case should be carried out under the most plausible condition. As a next step, conservative case should be defined considering the reasonable uncertainties with scientific basis.
Dei, Shuntaro; Tachi, Yukio; Amano, Yuki; Sugiura, Yuki; Francisco, P. C. M.; Takahashi, Yoshio*
no journal, ,
Saito, Takumi*; Nishi, Shusaku*; Sato, Hayato*; Miyakawa, Kazuya
no journal, ,
Dissolved organic matters (DOMs) play an important role for the fate of pollutants in surface and subsurface environments. For migration of radionuclides, the binding to DOMs modulates their aqueous speciation, reduce the adsorption on rock surface, and even enhance their transport, compared with non-sorbing tracers. The origin of DOMs in surface environments have been studied for decades and mechanistic models are proposed, which can describe ion-binding to major fractions DOMs (i.e. humic and fulvic fractions) over a wide range of environmental conditions. Nevertheless, our understanding on deep groundwater DOMs remains limited, and it is still disputable if model parameters calibrated for surface DOMs can be applied for their counterparts in deep subsurface environments. This study aims to reveal the origin of different DOM components in deep sedimentary groundwater and their ion-binding properties by fluorescence spectroscopy and high-resolution mass spectrometry. The results of both techniques are processed and correlated by multivariate analysis to find different DOM components and pursue their molecular characteristics. In the conference, we will present various molecular metrices describing the EEM components with the help of an advanced multivariate technique, which allows us to simultaneously process both the entire data sets of EEM and FT-ICR-MS data, consisting of the different data dimensions.
Mei, H.; Aoyagi, Noboru; Saito, Takumi*; Sugiura, Yuki; Ishidera, Takamitsu; Tanaka, Kazuya; Tachi, Yukio
no journal, ,
Haga, Yoshinori; Opletal, P.; Tokiwa, Yoshifumi; Yamamoto, Etsuji; Tokunaga, Yo; Kambe, Shinsaku; Sakai, Hironori
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Tanaka, Kazuya; Kurihara, Yuichi*; Tomita, Jumpei; Maamoun, I.; Yamasaki, Shinya*; Tokunaga, Kohei; Fukuyama, Kenjin*; Kozai, Naofumi
no journal, ,
We collected surface sediment and water samples at a U mill tailings pond in the Ningyo-toge center. Radioactivity concentrations of 
Ra in sediments were 12,000 - 29,000 Bq/kg while those in water ranged from 60 to 580 mBq/L. As a result, apparent distribution coefficients of Ra between ferric sediment and water were estimated to be 3.1 
10
- 3.8 10
mL/g, which were higher than reported ones for ferrihydrite and goethite. This suggests that another host on which Ra is strongly fixed would be present in sediment if we assume equilibrium between sediment and water. It is possible that Mn(IV) oxide as a minor component contributed to an increase in the apparent distribution coefficients. Another possibility is upward flow of pore water containing Ra or diffusion of Ra released from lower sediment layers. Either scenario provides additional input of Ra to surface sediment. In this case, surface sediment and water did not reach equilibrium with each other, but Ra concentrations in surface sediments were governed by dynamics through input of Ra from porewater as well as groundwater in sediment-water interaction.
) removal from aqueous solutions by mono-, bi-, and tri-metallic iron nanoparticles; A Comparative studyMaamoun, I.; Tokunaga, Kohei; Falyouna, O.*; Eljamal, O.*; Tanaka, Kazuya
no journal, ,