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JAEA Reports

Literature survey of redox reactions in the new field

Miki, Takahito*; Sasamoto, Hiroshi; Chiba, Tamotsu*; Inagaki, Manabu*; Yui, Mikazu

JNC-TN8400 2000-007, 32 Pages, 2000/01

JNC-TN8400-2000-007.pdf:0.69MB

This report presents a summary of literature survey about geochemical reactions which are important to evaluate the redox conditions in the near field rock mass and buffer. The results of literature survey are summarized as follows; (1)Minerals including ferrous iron and organic materials in the rock mass are important reductants. Initial stage after closure of repository, oxygen will be consumed by pyrite, because the reaction rate between pyrite and oxygen is relatively fast. (2)It is possible to estimate the redox capacity for reductants by rock (mineral)-water iteraction experiment in a laboratory. And it is expected that the ferrous iron-rich rock and higher porosity rock may have bigger redox capacity. (3)It is possible to estimate the oxygen consumption rate by reductants such as minerals including ferrous iron. The rate law and rate constant for the oxidation reaction of ferrous iron in the solution are also determined. As a conclusion, it seems that we can evaluate kinetically the evolution of geochemical conditions in the near field rock mass and buffer by excavation of drifts, based on data derived from these existing literatures.

JAEA Reports

QA issues for site hydrochemical data used for groundwater evolution models

Sasamoto, Hiroshi; Yui, Mikazu; D.Savag*; Bille, B.*

JNC-TN8400 99-025, 32 Pages, 1999/06

JNC-TN8400-99-025.pdf:1.94MB

Groundwater data used for modelling site or repository evolution need to be assessed for their quality and whether they are "fit for purpose", prior to utilization. This report discuss factors and issues which impinge upon the quality of such data. It is recommended that geochemical modelleres : (1)are aware of how groundwater samples were collected, whether during drilling, during hydraulic testing, or thereafter, by in-situ measurement, pumped from boreholes, or by pressurised sampler ; (2)are aware of what procedures (if any) were used to "correct" samples for drill fluid contamination and what errors were associated with those methods ; (3)are aware of whether samples were subject to de-pressurisation during sampling, and whether geochemical modelling techniques were applied to correct the compositions of samples for that process ; (4)request different measures of redox activity (e.g., electrode measurements of Eh, concentrations of different redox-sensitive aqueous species) to be applied to key groundwater samples to investigate the extent of redox equilibrium ; (5)are aware of how groundwater samples were filtered and preserved for off-site analysis ; (6)ensure that adequate methods of groundwater filtration ($$<$$ 0.1$$mu$$m) and chemical analysis are applied to ensure accurate and reproducible analyses for dissolved aluminum at low levels of concentration (generally less than 0.2 mg/L) ; (7)are aware of elemental errors and detection limits in chemical analysis of groundwater samples and assess the quality of groundwater analyses via ion exchange balances and via a comparison of measured and calculated values for total dissolved solids contents. (8)ensure that detailed mineralogical analysis is carried out on rock samples from locations where key groundwater samples have been extracted.

JAEA Reports

None

Imai, Hisashi*; Nishida, Kaoru*; *; Amemiya, Kiyoshi*; Lin, Weiren*

PNC-TJ1449 98-004, 231 Pages, 1998/02

PNC-TJ1449-98-004.pdf:16.85MB

None

Oral presentation

Effect of carbonate and redox conditions on uranium solubility and validation of thermodynamic calculations

Kitamura, Akira; Ito, Miki*; Akagi, Yosuke*; Yoshida, Yasushi*

no journal, , 

Effect of carbonate concentration and redox conditions on uranium solubility under geological disposal conditions was investigated. The applicability of predicted values using thermodynamic database was verified.

Oral presentation

Estimation of source term for spent fuel disposal, 2; Effect of carbonate concentration on dissolution rate of UO$$_{2}$$ and spent fuel; A Review

Kitamura, Akira; Akahori, Kuniaki*

no journal, , 

Since dissolution rate of UO$$_{2}$$ matrices will be depend on carbonate concentration due to promoting oxidative dissolution of spent nuclear fuel by formation of carbonate complexes of uranium(VI), effect of carbonate concentration on dissolution rate of UO$$_{2}$$ and spent nuclear fuel has been reviewed. It is found that a systematic study on dissolution rate of UO$$_{2}$$ and/or spent fuel as a function of carbonate concentration is recommended.

Oral presentation

Change of hydrochemical environment and relating process caused by construction and closing of underground facility

Watanabe, Yusuke; Hayashida, Kazuki; Murakami, Hiroaki; Iwatsuki, Teruki

no journal, , 

In the geological disposal project of high-level radioactive waste, a disposal facility will be constructed in depths deeper than 300 m. In this study, the simulated experimental tunnel was constructed in the granite of 500 m depth at Mizunami Underground Research Laboratory, and the hydrochemical process after the tunnel closure was observed.

Oral presentation

Research of microbial processes related to the formation of underground environment

Watanabe, Yusuke; Hayashida, Kazuki; Iwatsuki, Teruki; Suzuki, Yohei*

no journal, , 

The metabolic activities of microorganisms has potential to contribute for formation and keeping of redox condition in the groundwater. In particular, it is possible that the microbial sulfate reduction has great role in formation of reducing condition. However, in situ observation of the activities of sulfate reducing bacteria in the groundwater has not conducted. In this study, we examined relation of redox condition in groundwater with microbial activities by in situ incubation experiment of sulfate reducing bacteria living in borehole drilled in granitic rock at 300 m below ground level at the Mizunami Underground Research Laboratory.

Oral presentation

Variation of redox condition in groundwater during excavation

Watanabe, Yusuke; Hayashida, Kazuki; Murakami, Hiroaki; Iwatsuki, Teruki

no journal, , 

In assessing the safety of geological disposal of high-level radioactive waste, groundwater chemistry is an important factor influencing the performance of engineered materials and the behavior of radionuclides. It is essential to understand the hydrochemical changing process and stable condition after the closure of the disposal facilities. In this study, a simulated experimental drift was constructed in granite at a depth of 500 m at the Mizunami Underground Research Laboratory, and the hydrochemical condition and related processes after drift closure were observed.

Oral presentation

Change of hydrochemical environment and relating process associated with underground microbial activities

Watanabe, Yusuke; Fukuda, Kenji; Murakami, Hiroaki; Iwatsuki, Teruki; Suzuki, Yohei*

no journal, , 

Oxic condition may spread into the deep groundwater by penetrating of shallow oxic groundwater during construction and operation of geological repository for the geological disposal of nuclear waste. On the other hand, microbial activities living in deep underground such as sulfate reducing bacteria could keep the redox condition in groundwater reductive by the reduction of sulfate ion to hydrogen sulfide. In this study, in situ incubation experiment for sulfate reducing bacteria was conducted to observe its redox buffering capacity. Results showed that reducing condition was made by activities of sulfate reducing bacteria in the groundwater.

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