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Iwatsuki, Teruki; Amano, Yuki; Murakami, Hiroaki; Nanjo, Isao; Aoki, Kazuhiro; Sasaki, Yoshito; Yoshikawa, Hideki
no journal, ,
This study aims to develop the evaluation methods of environmental changes and the recovery process around a large underground facility. To this end, hydrochemical changes in response to shaft excavation are analyzed based on the observation of water pressure, groundwater chemistry and microbial community structure around the URL. Regarding the chemical disturbance in the area, the redox potential (ORPSHE) of the groundwaters in the monitoring boreholes showed reducing condition (around -200 - -250 mV with pH of approx. 6-7) nevertheless the gallery is in oxidized condition. Theoretical calculation and chemical/microbial analysis of water sample suggests that the dominant redox buffering process around gallery is water-mineral-microbe interaction including iron-, sulphur-bearing materials (mineral and solutes).
Ishii, Yasuo; Takahashi, Hiroaki; Tachi, Yukio; Tomura, Tsutomu*; Nemoto, Kazuaki*; Okazaki, Mitsuhiro*
no journal, ,
Am(III) diffusion experiment were performed by reservoir depletion (RD) test method coupled with thin layer ID profile fitting in 0.1 or 0.5M NaCl / 0.05M NaHCO
- bentonite (kunipia-F) system. The Kd values were also measured using batch technique in the same experimental conditions. In an ordinary ID profile acquisition cutting the bentonite by scraper, the compacted bentonite sample can be cut into 100 
m thick slices. Using this technique, it was possible to divide the ID profile into 10 m and therefore, to analyze diffusion distance layer larger than 50 m.
Tachi, Yukio; Yotsuji, Kenji; Suyama, Tadahiro; Nakazawa, Toshiyuki*; Shimoda, Satoko*; Kuno, Yoshio*
no journal, ,
Sorption and diffusion of radionuclides in compacted bentonite are key processes in the safe geological disposal. The effects of porewater pH and salinity on Ni sorption and diffusion in compacted montmorillonite were investigated by experimental and modeling approaches. Distribution coefficients (Kd) and effective diffusion coefficients (De) of Ni in montmorillonite compacted to dry density of 800 kg/m
were measured under four conditions with different pH (6, 8) and salinities (0.05, 0.5 M NaCl). The Kd increased with increasing pH and with decreasing salinity of porewater, which are consistent with batch-derived Kd trends. The De values changed with porewater salinity, which are independent of pH. Sorption and diffusion behaviors were interpreted by coupling the thermodynamic sorption model, and the diffusion model based on EDL theory in narrow pores. The mechanistic model could be useful in predicting the sorption and diffusion of high sorbing species in compacted systems.
Tachi, Yukio; Yotsuji, Kenji; Suyama, Tadahiro; Ochs, M.*; Yui, Mikazu
no journal, ,
Sorption and diffusion of radionuclides in compacted bentonite are the key processes in the safe geological disposal. JAEA has developed the integrated sorption and diffusion (ISD) model in compacted bentonite/montmorillonite systems. In this study, we focus on key challenges for testing the applicability of ISD model from dispersed batch systems to compacted ones, and from simple ions to complex species. The sorption model comprising 1-site non-electrostatic surface complexation model in combinations with 1-site ion exchange model, and the diffusion model based on electrical double layer theory in averaged narrow pores was coupled. The developed ISD model/database and results of their application to various radionuclides (Cs/Na, Cl/I, Am(III)/Eu(III), Th(IV), Np(V), U(VI)) are presented. The ISD model/database developed here provides a useful tool for a consistent explanation, prediction, and uncertainty assessment of Kd, De, Da parameters needed for the performance assessment.
Ishidera, Takamitsu; Baeyens, B.*; Marques, M.*; Glaus, M.*
no journal, ,
Ochs, M.*; Tachi, Yukio; Ganter, C.*; Suyama, Tadahiro; Yui, Mikazu
no journal, ,
The thermodynamic sorption models (TSMs) are being considered as powerful tools for quantifying the sorption of radionuclides for a given set of geochemical conditions, and especially for assessing the influence of variable geochemical conditions on the extent of sorption, for the performance assessment of disposal of radioactive waste. The aim of the present study is to address various aspects of TSM development that are important for lending credibility in the context of applications related to radioactive waste disposal. Specifically, the following points are addressed to use the example of Ni sorption to smectite: (1) evaluation of the experimental database and different modeling options in cases where different datasets are available, (2) representation of model uncertainties, (3) testing of the resulting TSM against additional data and evaluation of the applicability to more complex systems.
Iwata, Hajime*; Sakamaki, Keiko*; Yasuda, Kenichiro; Onuki, Toshihiko; Utsunomiya, Satoshi*
no journal, ,
The aim of this study is to understand the fate of plutonium derived from atomic bomb, which has been preserved in the bottom sediment for 60 years, based on the investigation of the speciation and size distribution of plutonium. Approximately 60 % of plutonium is present as bound to organic matters and 30 % is present as insoluble species such as Pu oxides. Our results also suggest that the fast transformation of plutonium to the species bound to the organic matter for the period of 60 years, evidencing the important role of the natural organic matters on the plutonium speciation in the environment.
Onuki, Toshihiko; Iwai, Wakari*; Kozai, Naofumi; Tanaka, Kazuya*; Suzuki, Yohei*
no journal, ,
In this study, we have conducted the research on the interaction of Np with Shewanella putrefaciens. The distribution coefficients of Np(V) after 2 h exposure was nearly the same as that after 4 h, indicating the adsorption of Np(V) by S. putrefaciens was attained equilibrium within 2 h. Higher Kd of Np was measured in the inert glove box than in the aerobic condition. These results indicate that Np(V) is adsorbed by the functional groups of S. putrefaciens, and Np(V) is reduced to Np(IV) by S. putrefaciens.
Jiang, M.; Onuki, Toshihiko; Tanaka, Kazuya*; Kozai, Naofumi; Kamiishi, Eigo; Utsunomiya, Satoshi*
no journal, ,
The objective of the present study is to further understand the post-adsorption process of middle REE (Sm) and heavy REE (Yb) biomineralization by several representative microbes for the long-term exposure. Based on the FESEM and TEM analyses, nano-sized Sm phosphate crystallites with monazite structure formed on these three kinds of microbial cells surfaces and nano-sized Yb phosphate with amorphous phase formed on yeast cells surfaces. The EXAFS data indicated that the chemical states of accumulated Sm and Yb on cells surfaces changed from the mixture of both phosphate and carboxyl sites at 30 min to phosphate precipitates phase at 5 days, suggesting the REE-phosphate mineralization as a major post-adsorption process.