Characterization of mineralogical controls on ammonium concentrations in deep groundwaters of the Horonobe area, Hokkaido

Sasamoto, Hiroshi; Sato, Hisao*; Arthur, R. C.*

Journal of Geochemical Exploration, 188, p.318 - 325, 2018/05

https://doi.org/10.1016/j.gexplo.2018.01.013

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.

Mineralogical, physical and chemical investigation of compacted Kunigel V1 bentonite in contact with a steel heater in the ABM test package 1 experiment, sp Laboratory, Sweden

Sasamoto, Hiroshi; Isogai, Takeshi*; Kikuchi, Hirohito*; Sato, Hisao*; Svensson, D.*

Clay Minerals, 52(1), p.127 - 141, 2017/03

https://doi.org/10.1180/claymin.2017.052.1.09

Compacted bentonite has been considered as a candidate of engineering barrier material in many countries for the safe disposal of high-level radioactive waste. SKB set up an in situ experiment (named ABM project) to compare the stability of different bentonites under the conditions exposed to an iron source and elevated temperature (up to 130C as maximum) at the sp Hard Rock Laboratory, Sweden. Results for the Japanese bentonite (Kunigel V1) are summarized in the present paper. Mineralogical investigation using X-ray diffraction (XRD) and X-ray spectroscopy (SEM-EDX) suggested that no indication of smectite transformation or newly formed clay phases were observed. However, a distinct change of exchangeable cations of smectite was indicated (i.e., from Na type to Fe type) in the bentonite at the vicinity of the steel heater. Physical investigation by measurements of hydraulic conductivity and swelling property suggested that no significant change occur in the bentonite even at the vicinity of the steel heater. Such results might be considered due to the limited portion affected by the iron-bentonite interactions and partially occurred ion exchange reactions. Chemical investigation based on the measurements of methylane blue (MB), cation exchange capacity (CEC) and exchangeable cations showed that the lateral distribution for these parameters were basically constant without the significant gradient.

Experimental study of alteration of bentonite coexisting iron material

Sasamoto, Hiroshi; Ishii, Tomoko*; Sato, Hisao*; Sazarashi, Masami

JAEA-Research 2010-030, 64 Pages, 2010/09

JAEA-Research-2010-030.pdf:15.41MB

It is necessary to evaluate the alteration behavior of buffer material by interactions of overpack (iron) and buffer (bentonite) materials for geological disposal of high level radioactive waste. In the present study, laboratory experiments were carried out for the better understanding of phenomena caused by iron-bentonite (smectite) interactions. Before conducting the experiments, literature survey was performed to summarize the existing knowledge about iron-bentonite interactions and to identify the dominant factors affecting the alteration behavior. As the results of experiment, experimental conditions caused remarkable alteration, secondary minerals suggested as alteration product, different behavior of alteration between batch and compacted systems etc. were revealed.

Experimental studies of iron-bentonite interactions under high temperature condition

Sasamoto, Hiroshi; Sazarashi, Masami; Ishii, Tomoko*; Sato, Hisao*; Kato, Hiroyasu*

no journal, , 

To investigate bentonite-iron interaction under high temperature condition, alteration experiments considering several factors (smectite composition, solution chemistry, iron-bentonite ratio) which were believed to affect on bentonite alteration were conducted with different experimental conditions. As the results, it was suggested that the factors considered in this study could also significantly affect on bentonite alteration in addition to temperature condition.

Experimental and modeling studies on iron-bentonite interactions

Sasamoto, Hiroshi; Wilson, J.*; Sato, Hisao*; Sazarashi, Masami

no journal, , 

The proposed repository design for high-level radioactive waste in Japan includes iron containers surrounded by a bentonite buffer. Interactions of iron-bentonite (I/B) materials may lead to the adverse transformation of smectite to phases with a limited capacity to swell. Batch experiments that included native iron powder and bentonite and column experiments whereby compacted bentonites were reacted with embedded iron coupons were conducted in order to evaluate the effects of environmental parameters on I/B interactions. Additionally, several model simulations have been produced in order to evaluate the factors influencing the nature of bentonite alteration in the presence of iron. The dominant process of interest over performance assessment timescales was estimated as the results of variant simulations.

Investigations of mineral alteration in Kunigel V1 samples contacted with iron obtained from long-term in-situ experiments

Ishidera, Takamitsu; Sasamoto, Hiroshi; Sato, Hisao*

no journal, , 

no abstracts in English

Effects of heterogeneity at fracture surface for tracer migration in a fractured crystalline rock from the Grimsel Test Site

Tachi, Yukio; Ito, Tsuyoshi; Akagi, Yosuke*; Sato, Hisao*; Martin, A. J.*

no journal, , 

The effects of heterogeneity at fracture surface on radionuclides migration in fractured crystalline rocks was investigated by laboratory migration experiments, microscopic observations and detailed modelling, using a single fractured granodiorite sample from the Grimsel Test Site (GTS), Switzerland. The tracer migration behaviors in fracture and matrix parts were evaluated by series of laboratory experiments including through-diffusion and flow-through experiments. Mineral distributions from fracture surface to matrix were evaluated by X-ray CT, and were validated by comparing the elemental mapping measured by EPMA. Based on the microscopic observations by X-ray CT and EPMA, the aperture and connectivity in fracture and minerals distribution near fracture surface were quantitatively evaluated. The heterogeneous multi-layered model assuming a weathered vermiculite zone, a foliated mica zone and rock matrix was possible to provide a reasonable interpretation for measured breakthrough curves of all tracers.

In situ interactions of concretes with mudstones from Horonobe URL

Anraku, Sohtaro; Sato, Hisao*; Walker, C.*; Amano, Yuki; Sakurai, Akitaka; Nakayama, Masashi; Tachi, Yukio

no journal, , 

Realistic modeling approach for radionuclide transport in heterogeneous fractured crystalline rocks

Tachi, Yukio; Ito, Tsuyoshi*; Fukatsu, Yuta; Akagi, Yosuke*; Sato, Hisao*; Martin, A. J.*

no journal, ,