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Koike, Ayaka*; Takubo, Yusaku*; Anraku, Sohtaro; Kawakita, Ryohei
NUMO-TR-24-03, p.62 - 64, 2024/10
no abstracts in English
Saito, Yuki*; Ishiwata, Tobimaru*; Horiuchi, Misato*; Nishiki, Yuto*; Kikuchi, Ryosuke*; Otake, Tsubasa*; Kawakita, Ryohei; Takayama, Yusuke; Mitsui, Seiichiro; Sato, Tsutomu*
Shigen, Sozai Koenshu (Internet), 11(1), 7 Pages, 2024/03
no abstracts in English
Yanagida, Akinobu*; Ura, Yoko*; Mitsui, Seiichiro; Ishidera, Takamitsu; Kawakita, Ryohei
Nara Bunkazai Kenkyujo Soritsu 70-Shunen Kinen Rombunshu; Bunkazai Ronso 5, p.843 - 856, 2023/03
To investigate chloride salt accumulation inside an iron artifact in soil, non-destructive analysis of three iron artifacts excavated from the Heijo Palace Site was conducted using elemental mapping by X-ray fluorescence analysis, micro-X-ray diffraction analysis, and X-ray computed tomography. Furthermore, the buried environments of the artifacts were presumed based on the previous reports of the environmental investigation at the Heijo Palace site. The results revealed the iron artifact's corrosion behavior was different individually- (1) the iron artifact that was presumed buried under oxidation environments had a goethite/magnetite corrosion layer and contained akageneite inside the corrosion layer. (2) the metal of the other iron artifacts buried under the oxidation environment had eluted absolutely and the artifacts had a rust layer formed by only goethite. (3) the other artifact buried in reduction environments had a rust layer composed of siderite. Accumulation of chloride salts inside an iron artifact was observed only in (1). Because each Cl
concentration measured in underground water observation holes at the Heijo Palace Site showed almost the same level concentrations, it was presumed that the accumulation of chloride salts depended on the environmental factor except for Cl concentration. Based on these results, there was a possibility that the occurrence of local corrosion attributed to the separation of anodic and cathodic regions through the formation of the goethite/magnetite rust layer caused chloride salts accumulation inside an iron artifact.
- and K-montmorilloniteKawakita, Ryohei; Saito, Akito*; Sakuma, Hiroshi*; Anraku, Sohtaro; Kikuchi, Ryosuke*; Otake, Tsubasa*; Sato, Tsutomu*
Applied Clay Science, 231, p.106722_1 - 106722_7, 2023/01
Times Cited Count：2 Percentile：23.28(Chemistry, Physical)Matsuura, Hideharu*; Iwata, Hiroshi*; Kagamihara, So*; Ishihara, Ryohei*; Yoneda, Masahiko*; Imai, Hideaki*; Kikuta, Masanori*; Inoue, Yuki*; Hisamatsu, Tadashi*; Kawakita, Shiro*; et al.
Japanese Journal of Applied Physics, Part 1, 45(4A), p.2648 - 2655, 2006/04
Times Cited Count：15 Percentile：48.68(Physics, Applied)no abstracts in English
-montmorilloniteKawakita, Ryohei*; Saito, Akito*; Sakuma, Hiroshi*; Anraku, Sohtaro; Oda, Chie; Mihara, Morihiro; Sato, Tsutomu*
no journal, ,
no abstracts in English
Ichikawa, Nozomi*; Hamamoto, Takafumi*; Sasamoto, Hiroshi; Ichige, Satoru*; Kawakita, Ryohei; Fujisaki, Kiyoshi*
no journal, ,
For model validation of bentonite behavior under high alkaline condition, a batch type reaction experiment and modeling were performed. In the batch type reaction experiment, simulated solutions for the leachate from cement material (Region I solution of pH13 simulated by mixture of both 0.2M NaOH and KOH solutions, Region II solution of pH12.5 simulated by 0.016M CaOH
solution) and bentonite (Kunigel V1 and Kunipia F) were reacted under L/S ratio of 50 mL/g and temperature for either 25 or 50 degrees, and for 2 years as the maximum duration. As the results, for example of the experiment for reactions between Region I solution and Kunipia F at 50 degrees, the peak intensity for montmorillonite slightly decreased with time and the new formed secondary mineral suggested as phillipsite occur. Geochemical modeling for this experimental case was performed. Regarding the amount of montmorillonite dissolution, the modeling considering the reactions of both montmorillonite dissolution and ion exchange approximated the experimental result well, however, the addition of the secondary mineral precipitation reaction was less effective. Sensitivity analyses considering the parameter uncertainties of secondary mineral precipitation reaction stimulated that the inconsistency was not dependent on the parameter uncertainties.
Ishiwata, Tobimaru*; Kikuchi, Ryosuke*; Otake, Tsubasa*; Sato, Tsutomu*; Kawakita, Ryohei; Takayama, Yusuke; Mitsui, Seiichiro
no journal, ,
It is known that the cementation of bentontie may cause the reduction of swelling pressure. However, fundamental mechanism of this reducing swelling pressure has not been well understood. To understand the mechanism, it is essential to identify the cementitious materials and observe the changes in microstructure associated with cementation. In this study, the microstructural observation and swelling tests were conducted on several bentonite ores collected from Tsukinuno Mine in Yamagata Prefecture, Japan, as natural analog of cementation, and the relationship between petrographic texture and swelling pressure was discussed. Thin sections of bentonite ores were prepared by dry polishing technique to observe flat surfaces in micro scales. Scanning electron microscopy (SEM) demonstrated the widespread distribution of authigenic, a few micron silica in the matrix of montmorillonite. Transmission electron microscopy (TEM) revealed that the micro silica minerals (commonly quartz and less commonly amorphous silica) adhered to the edge of montmorillonite grains. These observations suggest that the adherence of these cementitious materials to montmorillonite prevents water access to the interlayer of montmorillonite and swelling, resulting in a decrease in swelling pressure. While these microstructures were observed commonly in all samples collected from several bentonite beds, the relative abundance of montmorillonite and micro silica minerals varied among different beds. It is possible that the swelling pressure in the cemented bentonite is affected by the relative abundance of montmorillonite and cementitious materials.
Mitsui, Seiichiro; Kawakita, Ryohei; Ishidera, Takamitsu
no journal, ,
Evaluation of geological disposal deals with long-term time scales of hundreds to tens of thousands of years. On the other hand, our experiments are limited to about 20 years at the longest, and it is possible that the long-term phenomena assumed in geological disposal have not been sufficiently simulated. Regarding the corrosion behavior of carbon steel overpacks, the corrosion depths over time in immersion tests for several to ten years can be approximated by a power law. From the fact that a protective corrosion product film, such as siderite, was observed on the surface of the test piece, it is believed that this can be explained by the passive effect of the corrosion product film on the corrosion reaction. However, the effect cannot be applied to the long-term corrosion behavior based solely on the results of immersion tests. Through natural analogue studies, we concluded that the passive effect of the corrosion product film can explain long-term corrosion behavior exceeding hundreds of years.
Saito, Akito*; Kawakita, Ryohei*; Sakuma, Hiroshi*; Oda, Chie; Honda, Akira; Sato, Tsutomu*
no journal, ,
To understand the swelling behavior of NH
-montmorillonite (MMT), the expandability of monoionic Na-, K- and NH-MMT was investigated by XRD under controlled relative humidity (RH) conditions and molecular dynamics (MD) calculations. XRD results indicate that the expansion properties of NH-MMT are similar to that of K-MMT for RH 
30%. At RH 
30%, however, NH-MMT expands further and has a larger basal spacing than both Na- and K-MMT. MD calculation results showed that NH-MMT reaches a one-layer hydration state under lower RH conditions than that of Na- and K-MMT, and was entirely consistent with the above observations by XRD. It was also confirmed that an irregular motion of interlayer NH
could result from bonds between H atoms of the NH ion and the base O atoms of MMT. This irregular motion enabled the basal spacing of NH-MMT to increase and consequently, to expand further under low RH conditions.
Anraku, Sohtaro; Kawakita, Ryohei; Hanamachi, Yuji*; Mitsui, Seiichiro; Sasamoto, Hiroshi; Mihara, Morihiro
no journal, ,
To evaluate the observed alteration of bentonite and secondary mineral formation by OPC or HFSC near the interface, 1D reactive transport models were constructed using the Cement And Bentonite Alteration due to REactive Transport (CABARET) computer modelling code. Supporting calculations for initial hydration of OPC or HFSC were conducted using PHREEQC to generate the initial porewater compositions. JAEA's Thermodynamic DataBase for geochemical reaction was used in all calculations. Modeling of OPC and Kunigel V1 interaction resulted in depletion of Ca in OPC by portlandite dissolution and depletion of Si in Kunigel V1 by chalcedony dissolution leading to C-S-H gel precipitation at the interface, which were confirmed by XRD. Clogging of the interface by the precipitation of C-S-H gel at 80
C, however, limited diffusion and therefore the alteration of Kunigel V1. Coupling between diffusion coefficients and low porosities requires further data and validation to improve the simulation. The temperature dependence of dissolution rates of the C-S-H gel and chalcedony also needs to be confirmed. Modeling of HFSC and Kunigel V1 interaction showed significantly less alteration of the Kunigel V1 from the significantly less alkaline HFSC porewater, which is also consistent with the experiments. Modelled changes in HFSC resulted in an increase in porosity at the interface by the dissolution of C-A-S-H gel and ettringite, and in Kunigel V1 by the slight dissolution of chalcedony. To evaluate the elevated temperature effect in HFSC hydration, it is important to use a C-A-S-H gel model and to confirm the extents of pozzolanic reaction of silica fume and fly ash, which are currently based on measurements at room temperature.
Kawakita, Ryohei*; Saito, Akito*; Sakuma, Hiroshi*; Anraku, Sohtaro; Oda, Chie; Mihara, Morihiro; Sato, Tsutomu*
no journal, ,
no abstracts in English
derived from TRU waste containing nitrateKawakita, Ryohei; Sasamoto, Hiroshi; Mihara, Morihiro
no journal, ,
no abstracts in English
Kawakita, Ryohei; Anraku, Sohtaro; Hanamachi, Yuji*; Mitsui, Seiichiro; Sasamoto, Hiroshi; Mihara, Morihiro
no journal, ,
Cement and bentonite materials are to be used in a repository for the geological disposal of radioactive wastes in Japan. Cement will provide structural support to the repository and will be in close contact with bentonite. Understanding the interactions between these two materials is necessary to improve repository design and ensure long-term safety. Ordinary Portland Cement (OPC) is widely used for construction, however, there are concerns that its high pH 13 porewater could cause significant alteration of bentonite. JAEA has therefore developed a High-content Fly ash Silica fume Cement (HFSC) to lower the pH of cement porewater. Studies on HFSC and bentonite interactions are, however, limited. In addition, elevated temperatures can be expected in the repository by the combination of radiolytic heating and geothermal gradients. Temperature affects mineral reaction rates and their overall stability, but such thermal effects have not yet been studied in detail in the context of cement and bentonite interactions. Laboratory scale experiments were therefore conducted to investigate the interactions between OPC or HFSC and compacted bentonite (Kunigel V1; dry density = 1.37 Mg/m
) at repository relevant temperatures of 50C and 80C.
Ishiwata, Tobimaru*; Kikuchi, Ryosuke*; Otake, Tsubasa*; Sato, Tsutomu*; Kawakita, Ryohei; Takayama, Yusuke; Mitsui, Seiichiro
no journal, ,
Bentonite clay is planned to be used as a buffer material in the geological disposal of high-level radioactive wastes. The swelling property of bentonite is expected to keep low permeability and control the migration of radionuclides thereby ensuring the safety of geological disposal. In the long-term, however, cementation of bentonite may degrade the swelling property where secondary minerals precipitate and adhere to the montmorillonite component of bentonite. In the present study, natural bentonite ores were investigated as analogues to cementation of bentonite in geological disposal. The images of SEM and EPMA were integrated into "mineral map", which could visually illustrate the distributions of individual mineral grains including fine cementitious minerals. Finally, multi regression analysis (MRA) was used to investigate correlation between petrographic parameters and swelling pressure. MRA showed swelling pressure of bentonite increases with the content of montmorillonite, and decreases with the total perimeter of accessary minerals. This suggests that the presence of secondary minerals can inhibit the swelling of montmorillonite and the area of contact between montmorillonite and secondary minerals might be a key parameter.
