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Journal Articles

Mechanism of alkalinity lowering and chemical equilibrium model of high fly ash silica fume cement

Hoshino, Seiichi; Negishi, Kumi*; Honda, Akira

Konkurito Kogaku Rombunshu, 25, p.97 - 107, 2014/05

A pH lowering mechanism of highly flyash contained silicafume cement (HFSC) in Region I and the chemical equilibrium model of HFSC incorporating the mechanism were studied. As a result, it is suggested that the dissolution and precipitation behavior of SO$$_{4}$$$$^{2-}$$ partially contributes to the pH lowering of HFSC in Region I. A chemical equilibrium model of HFSC incorporating alkali (Na, K) adsorption, which was supposed as another contributing factor of pH lowering effect, was also developed, and immersion experiment of HFSC was analyzed using the model. The calculated results by the developed model were in agreement with the experiment results. From the above results, it was concluded that the pH lowering of HFSC in Region I was attributed to both of the dissolution and precipitation behavior of SO$$_{4}$$$$^{2-}$$ and the alkali adsorption.

Journal Articles

Modeling of diffusive mass transport in micropores in cement based materials

Yamaguchi, Tetsuji; Negishi, Kumi*; Hoshino, Seiichi; Tanaka, Tadao

Cement and Concrete Research, 39(12), p.1149 - 1155, 2009/12

 Times Cited Count:22 Percentile:36.2(Construction & Building Technology)

In order to predict long-term leaching behavior of cement constituents in safety assessments of radioactive waste disposal, we modeled diffusive mass transport in micropores cement based materials. Based on available knowledge on the pore structure, we developed a transport porosity model that enables us to estimate effective porosity available for diffusion (transport porosity) in cement based materials. We microscopically examined the pore structure of hardened cement pastes to partially verify the model. Effective diffusivities of tritiated water in hardened cement pastes were also obtained experimentally, and were shown to be proportional to the estimated transport porosity. We successfully modeled the effective diffusivity in cement based materials consistent with previously acknowledged pore diffusion model.

JAEA Reports

Evaluation method of pH elevation due to reaction between hydrates of ordinary Portland cement and saline groundwater

Masuda, Kenta; Oda, Chie; Nakanishi, Hiroshi*; Sasaki, Ryoichi*; Takase, Toshio*; Akagi, Yosuke*; Fujita, Hideki*; Negishi, Kumi*; Honda, Akira

JAEA-Research 2008-104, 194 Pages, 2009/03

JAEA-Research-2008-104.pdf:9.43MB

Saline groundwater contains high concentrations of chloride ions, which possibly elevate the pH of cement pore water by reacting with hydrogarnet and producing Friedel's salt. Calcium aluminate hydrates and portlandite, which can be found in hydrated ordinary Portland cement (OPC), were immersed in a sodium chloride solution, which had concentrations similar to those found in seawater.

Journal Articles

Modeling of pH elevation due to the reaction of saline groundwater with hydrated ordinary Portland cement phases

Honda, Akira; Masuda, Kenta; Nakanishi, Hiroshi*; Fujita, Hideki*; Negishi, Kumi*

Materials Research Society Symposium Proceedings, Vol.1124, p.365 - 372, 2009/00

Journal Articles

The Influence of nitrate on dissolution behavior of cement hydrates

Fujita, Hideki*; Negishi, Kumi*; Osawa, Tsutomu*; Honda, Akira

Semento, Konkurito Rombunshu, (61), p.262 - 269, 2008/02

The influence of sodium nitrate on dissolution of cement hydrates was investigated by flow through experiment. Dissolution of portlandite was accelerated in NaNO$$_{3}$$ solution of 1 mol dm$$^{-3}$$ than in ion exchanged water. The acceleration of portlandite dissolution attributed to impact of ionic strength on the activities of aqueous species, because Ca concentration in 1 mol kg$$^{-1}$$ NaNO$$_{3}$$ solution equilibrated with portlandite was estimated to be 1.5 times as high as that in pure water. After flow through experiment, compressive strength fell down and porosity was higher than blank test using pure water. However low permeabilities were contradictory kept during NaNO$$_{3}$$ solution flowing. Dense existence of Na was possible to cause the low permeability during NaNO$$_{3}$$ solution flowing.

Journal Articles

Development and verification of a reactive transport model for long-term alteration of bentonite-cement-seawater systems

Yamaguchi, Tetsuji; Yamada, Fumika; Negishi, Kumi*; Hoshino, Seiichi; Mukai, Masayuki; Tanaka, Tadao; Nakayama, Shinichi

Physics and Chemistry of the Earth, 33(Suppl.1), p.S285 - S294, 2008/00

It is important to assess long-term alteration of engineered barrier composed of bentonite and cement for the safety assessment of radioactive waste disposal. In order to promote our development of the assessment methodologies, we developed a secondary mineral formation model for cement based materials and a hydraulic conductivity model for bentonite buffer materials. These models were verified by comparing with experimental observations. We also calculated changes in mineralogy of bentonite buffer materials and accompanying changes in the hydraulic conductivity over 10,000 y. We identified the temperature as an important factor dominating the alteration of the buffer. We also identified that the alteration is limited by slow kinetics of the dissolution of montmorillonite and by the diffusive mass transfer. Our calculation showed that the mineralogical change proceeds rather fast during the initial 1,000 y and slows down afterwards, and that salinity of the groundwater has both positive and negative effects on the hydraulic conductivity.

Journal Articles

Experimental study on long-term safety assessment considering uncertainties for geological disposal of radioactive wastes; JAERI status at 2005

Yamaguchi, Tetsuji; Sakamoto, Yoshifumi; Iida, Yoshihisa; Negishi, Kumi; Taki, Hiroshi; Akai, Masanobu; Jinno, Fumika; Kimura, Yuichiro; Ueda, Masato; Tanaka, Tadao; et al.

Proceedings of International Conference on Nuclear Energy System for Future Generation and Global Sustainability (GLOBAL 2005) (CD-ROM), 6 Pages, 2005/10

no abstracts in English

Journal Articles

Long-term alteration of bentonite; For safety evaluation of deep geological disposal

Tanaka, Tadao; Sakamoto, Yoshifumi; Yamaguchi, Tetsuji; Takazawa, Mayumi; Akai, Masanobu; Negishi, Kumi; Iida, Yoshihisa; Nakayama, Shinichi

JAERI-Conf 2005-007, p.105 - 110, 2005/08

Highly alkaline environments induced by cementitious materials in radioactive waste repositories are likely to dissolve and to alter montmorillonite, the main constituent of bentonite buffer materials. For the prediction of the long-term variations in permeability of compacted sand-bentonite mixtures, long-term alteration of bentonite should be quantified based on information accumulated by using the compacted or powdered bentonite materials, with batch experiments or column experiments. In this study, we summarize distinctive information obtained from various experimental systems, and propose functional and effective integration of experimental approaches to prediction of bentonite alteration.

Journal Articles

Data acquisition on migration of radionuclides under deep geological environments

Iida, Yoshihisa; Taki, Hiroshi; Yamaguchi, Tetsuji; Tanaka, Tadao; Negishi, Kumi; Nakayama, Shinichi

JAERI-Conf 2005-007, p.230 - 235, 2005/08

A variation in data should be quantitatively incorporated in a probabilistic safety assessment of radioactive waste disposal. We focus our experimental efforts on parameters that induce major uncertainties in the radionuclide migration analysis and that have not been quantitatively assessed. Possible sources of uncertainty includes increase in ionic strength of groundwater caused by intrusion of seawater and/or dissolution of sodium nitrate in TRU waste, highly alkaline conditions originating from cementitious materials, and a variation of porewater composition accompanied with corrosion of. This study is a summary of current status of our investigations for solubility and diffusion.

Journal Articles

Experimental and modeling study to predict long-term alteration of bentonite buffer materials with alkaline groundwater

Takazawa, Mayumi; Negishi, Kumi; Sakamoto, Yoshifumi; Akai, Masanobu; Yamaguchi, Tetsuji; Iida, Yoshihisa; Tanaka, Tadao; Nakayama, Shinichi

JAERI-Conf 2005-007, p.236 - 241, 2005/08

no abstracts in English

Journal Articles

Experimental study for predicting long-term performance of radioactive waste disposal, 2; Experimental data acquisition on radionuclide migration

Yamaguchi, Tetsuji; Negishi, Kumi; Ebashi, Katsuhiro; Inagaki, Shingo*; Shibata, Mitsunobu*; Tanaka, Tadao; Nakayama, Shinichi

JAERI-Conf 2004-011, p.139 - 140, 2004/07

Uncertainties should be quantitatively assessed in a long-term assessment of radioactive waste disposal. We focus our experimental efforts on parameters that induce major uncertainties in the radionuclide migration analysis and that have not been quantitatively understood. Solubility of radionuclides, diffusion in bentonite buffer material and sorption on rocks were investigated to quantify the uncertainties associated with the parameters and to minimize the uncertainties.

JAEA Reports

Study on the Alteration of Hydrogeological and Mechanical Properties of the Cementitious Material II

Takei, Akihiko*; Owada, Hitoshi*; Fujita, Hideki*; Negishi, Kumi*; Hibiya, Keisuke*; Yokozeki, Kosuke*; Watanabe, Kenzo*

JNC-TJ8400 2003-047, 120 Pages, 2003/02

JNC-TJ8400-2003-047.pdf:4.46MB

We acquired the water permeation properties and also mechanical characteristics of the altered specimen that produced by permeation or immersing as the fundamental data.

JAEA Reports

Study on the Alteration of Hydrogeological and Mechanical Properties of the Cementitious Material II

Takei, Akihiko*; Owada, Hitoshi*; Fujita, Hideki*; Negishi, Kumi*; Hibiya, Keisuke*; Yokozeki, Kosuke*; Watanabe, Kenzo*

JNC-TJ8400 2003-046, 282 Pages, 2003/02

JNC-TJ8400-2003-046.pdf:8.26MB

We acquired the water permeation properties and also mechanical characteristics of the altered specimen that produced by permeation or immersing as the fundamental data.

JAEA Reports

The Effect of Nitrates on the Alteration of the Cementitious Material II

Takei, Akihiko*; Owada, Hitoshi*; Fujita, Hideki*; Negishi, Kumi*

JNC-TJ8400 2003-042, 67 Pages, 2003/02

JNC-TJ8400-2003-042.pdf:4.7MB

TRU waste includes various chemical compounds such as nitrates. The influence of the chemical compounds on the performance of the barrier system should be estimated. In this study, we estimated the influence of sodium nitrate and also that of the chemical compounds derived from the sodium nitrate to the degradation of the cementitious material. 1) Evaluation of the influence of nitrate ion on the alteration of the cementitious material Alteration of characteristics of cementitious material was evaluated by the water permeation test using sodium nitrate solution. The calcium concentration of sodium nitrate solution permeated sample was higher than that of blank. The result indicates that sodium nitrate solution will accelerate the alteration of cementitious material. the permeation test was continued by using the ion-exchanged water as the permeation-water. As the results, the chemical and physical characteristics of the samples approached to those of blanks.2) Evaluation of the influence of ammonia on the alteration of the cementitious material Alteration of characteristics of cementitious material in nitrate and ammonia solution was evaluated by the water permeation test using 1mol/liter-sodium-nitrate and 0.5mol/liter-ammonia solution (denoted as NH-solution in the following). The calcium concentration of NH-solution permeated sample was higher than that of blank and the value of the calcium concentration was almost the same as that of the sodium nitrate solution case. The alteration range by the calcium leaching of the solid phase of the NH-solution case shows similar trend to that of the sodium nitrate solution case. The acceleration of the calcium dissolution was considered from this result. And the change of the water-permeability indicated the same trend with sodium-nitrate-solution case. From these results we confirmed that ammonia solution would not influence the alteration of cementitious solution.

JAEA Reports

The Effect of Nitrates on the Alteration of the Cementitious Material II

Takei, Akihiko*; Owada, Hitoshi*; Fujita, Hideki*; Negishi, Kumi*

JNC-TJ8400 2003-041, 152 Pages, 2003/02

JNC-TJ8400-2003-041.pdf:7.93MB

TRU waste includes various chemical compounds such as nitrates. The influence of the chemical compounds on the performance of the barrier system should be estimated. In this study, we estimated the influence of sodium nitrate and also that of the chemical compounds derived from the sodium nitrate to the degradation of the cementitious material. 1) Evaluation of the influence of nitrate ion on the alteration of the cementitious material Alteration of characteristics of cementitious material was evaluated by the water permeation test using sodium nitrate solution. The calcium concentration of sodium nitrate solution permeated sample was higher than that of blank. The result indicates that sodium nitrate solution will accelerate the alteration of cementitious material. the permeation test was continued by using the ion-exchanged water as the permeation-water. As the results, the chemical and physical characteristics of the samples approached to those of blanks. 2) Evaluation of the influence of ammonia on the alteration of the cementitious material Alteration of characteristics of cementitious material in nitrate and ammonia solution was evaluated by the water permeation test using 1mol/liter-sodium-nitrate and 0.5mol/liter-ammonia solution (denoted as NH-solution in the following). The calcium concentration of NH-solution permeated sample was higher than that of blank and the value of the calcium concentration was almost the same as that of the sodium nitrate solution case. The alteration range by the calcium leaching of the solid phase of the NH-solution case shows similar trend to that of the sodium nitrate solution case. The acceleration of the calcium dissolution was considered from this result. And the change of the water-permeability indicated the same trend with sodium-nitrate-solution case. From these results we confirmed that ammonia solution would not influence the alteration of cementitious solution.

Oral presentation

Development of a coupled mass-transport/chemical reaction code for simulating variation in hydraulic conductivity of bentonite buffer in radioactive waste disposal

Yamada, Fumika; Yamaguchi, Tetsuji; Maeda, Toshikatsu; Mizuno, Tsuyoshi; Sakamoto, Yoshifumi*; Negishi, Kumi*; Tanaka, Tadao; Iida, Yoshihisa

no journal, , 

no abstracts in English

Oral presentation

Investigation of pH elevation caused by reaction between cement hydrates and saline water

Nakanishi, Hiroshi; Honda, Akira; Oda, Chie; Sasaki, Ryoichi; Fujita, Hideki*; Negishi, Kumi*; Takase, Toshio*; Akagi, Yosuke*

no journal, , 

no abstracts in English

Oral presentation

Experimental research for long term evaluation on radioactive waste disposal; Progress in 2006

Tanaka, Tadao; Yamaguchi, Tetsuji; Iida, Yoshihisa; Kimura, Yuichiro; Taki, Hiroshi; Fujiwara, Takeshi; Ueda, Masato*; Mukai, Masayuki; Yamada, Fumika; Mizuno, Tsuyoshi; et al.

no journal, , 

no abstracts in English

Oral presentation

Diffusivity in hardened cement paste altered by contacting aqueous carbonate solutions

Hoshino, Seiichi; Yamaguchi, Tetsuji; Mukai, Masayuki; Yamada, Fumika; Negishi, Kumi*; Tanaka, Tadao; Nakayama, Shinichi

no journal, , 

no abstracts in English

Oral presentation

Experimental research for long term evaluation on radioactive waste disposal; Progress in 2007, Approach to modeling of alteration of cement based materials

Hoshino, Seiichi; Yamada, Fumika; Negishi, Kumi*; Mukai, Masayuki; Iida, Yoshihisa; Yamaguchi, Tetsuji; Tanaka, Tadao; Nakayama, Shinichi

no journal, , 

no abstracts in English

23 (Records 1-20 displayed on this page)