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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
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 and the alkali adsorption.
Yamaguchi, Tetsuji; Negishi, Kumi*; Hoshino, Seiichi; Tanaka, Tadao
Cement and Concrete Research, 39(12), p.1149 - 1155, 2009/12
Times Cited Count：29 Percentile：65.2(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.
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.
Honda, Akira; Masuda, Kenta; Nakanishi, Hiroshi*; Fujita, Hideki*; Negishi, Kumi*
Materials Research Society Symposium Proceedings, Vol.1124, p.365 - 372, 2009/00
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
solution of 1 mol dm
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
NaNO 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 solution flowing. Dense existence of Na was possible to cause the low permeability during NaNO solution flowing.
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.
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
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.
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.
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
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.
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.
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.
Takei, Akihiko*; Owada, Hitoshi*; Fujita, Hideki*; Negishi, Kumi*
JNC TJ8400 2003-042, 67 Pages, 2003/02
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.
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.
; *; Owada, Hitoshi*; *; *
JNC TJ6400 2003-001, 44 Pages, 2003/02
JNC-TJ6400-2003-001.pdf:3.09MB
None
; *; Owada, Hitoshi*; *; *
JNC TJ6420 2002-007, 28 Pages, 2002/03
JNC-TJ6420-2002-007.pdf:0.38MB
None
*; Owada, Hitoshi*; Fujita, Hideki*; *
JNC TJ8400 2002-033, 60 Pages, 2002/02
JNC-TJ8400-2002-033.pdf:1.97MB
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. Since the temperature of the deep-underground is higher than that of the near surface and a part of the TRU waste generates the heat accompanied with the decay of the radioactive nuclides, the influences of the heat to the barrier material also should be taken into account. In this study, we estimated the influence of sodium nitrate and also that of the leachate from the ROBE-waste (borate-solidified body of concentrated low-level liquid waste) to the degradation of the cementitious material. We also obtained the mineralogical data of cementitious mineral after alteration in elevated temperature conditions. Results in this year are described below. (1)Alteration of characteristics of cementitious material in nitrate solution were evaluated by the water permeation test using sodium nitrate solution. The enhancement of the alteration of cementitious material due to sodium nitrate was observed. The dissolution quantity of the calcium of sodium nitrate solution permeated sample was larger than that of deionized water permeated sample (denoted as "blank" in following). Hydraulic conductivity of sodium nitrate solution permeated sample was lower than blank, but after changing permeation liquid from sodium nitrate solution to deionized water, hydraulic conductivity rose quickly. The increase of porosity and the decrease of compressive strength were observed in the case of sodium nitrate solution compared with blank. In the nitrate solution, sulfate type and carbonate type of AFm changed into the nitrate type AFm. The nitrate type AFm altered to the carbonate type AFm when the nitrate concentration was lowered. (2)The influence of the leachate from the two types of ROBE-waste on the dissolution of the cementitious material was evaluated by the leaching experiments. Dissolution of the calcium from the ...
*; Owada, Hitoshi*; Fujita, Hideki*; *; *; Yokozeki, Kosuke*; *
JNC TJ8400 2002-029, 79 Pages, 2002/02
JNC-TJ8400-2002-029.pdf:1.58MB
We acquired the water permeation properties and also mechanical characteristics of the altered specimen that produced by permeation or leaching as the fundamental data for the evaluation in "Study on the system development for evaluating long-term alteration of hydraulic field in Near Field" that had been carried out separately. The results in this year are shown below. (1)Hardened cement paste specimens with W/C=85% and 105% were altered and characterized after permeation. Permeability of altered part was increased, as permeated water increased. Porosity was increased at the upper part of altered specimens, and compressive strength that means the properties from altered part of specimens were decreased after water-permeation. Adequate correlations are estimated between compressive strength and porosity, permeability, Vickers hardness. From the chemical properties, it is presumed these physical changes were caused by dissolution of portlandite. (2)Hardened cement paste specimens with W/C=40 to 105% were immersed into deionized water and alteration behavior under diffusion condition was investigated. As a result, after 12 weeks, porosity was increasing and Vickers hardness was decreasing at the altered area. And the water permeability and the compressive strength at the deteriorated area were simulated from relations between water permeability, compressive strength, porosity, Vickers hardness and leaching ratio of calcium. These results suggest that two methods (permeation and leaching) make up for fault of each other. It is necessary to prepare additional data, to clarify the relations between each alteration factor.
