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Irisawa, Keita; Namiki, Masahiro*; Taniguchi, Takumi; Garcia-Lodeiro, I.*; Kinoshita, Hajime*
Cement and Concrete Research, 156, p.106758_1 - 106758_8, 2022/06
Times Cited Count：12 Percentile：61.72(Construction & Building Technology)Cementation of aqueous radioactive waste contaminated with a significant 
Sr is challenging, and utilization of calcium aluminate cement (CAC) modified with sodium polyphosphate (CAP) is interesting. The present study investigated solidification and stabilization of Sr
and Cl
ions in CAC and CAP cured in open system at 90
C and in closed system at 20C. A leaching test showed that Sr ion could be stabilized more effectively in the CAP than in the CAC. On the other hand, the CAC cured at 20C had the best stabilization for Cl ion among the samples. Friedel's salt formed in the CAC may have contributed to the immobilization of Cl ion. Although the stabilization of Cl ion by CAP was less effective than CAC, it was significantly improved by the thermal treatment. The results may suggest that Cl ion in the CAP was incorporated in the poorly crystalline apatite structure.
Irisawa, Keita; Garcia-Lodeiro, I.*; Kinoshita, Hajime*
Cement and Concrete Research, 128, p.105951_1 - 105951_7, 2020/02
Times Cited Count：11 Percentile：39.28(Construction & Building Technology)This study investigated characteristics of a calcium aluminate cement modified with a phosphate (CAP) by changing an amount and concentration of mixing solution with sodium polyphosphate. When the amount of mixing solution was increased with a constant amount of sodium polyphosphate, an enhanced consumption of monocalcium aluminate was observed compared with gehlenite in calcium aluminate cement (CAC). Formation of gibbsite, Al(OH)
, was also increased as a hydration product in the CAP and the possible reduction of water in the amorphous gel phase. When the amount of mixing solution was increased with a constant concentration of sodium polyphosphate, the enhanced consumption of monocalcium aluminate was not observed. Neither gibbsite nor any other crystalline hydration products were identified in this series. In addition, unreacted sodium polyphosphate remained in the system. The increased formation of gibbsite and the possible reduction of water from the amorphous gel phase appears to contribute to the improvement of the microstructure in the products.
Garcia-Lodeiro, I.*; Irisawa, Keita; Meguro, Yoshihiro; Kinoshita, Hajime*
Proceedings of 15th International Congress on the Chemistry of Cement (ICCC 2019) (Internet), 10 Pages, 2019/09
The immobilization of low or intermediate-level radioactive wastes in cements is a common practise. Grout, a mixture of Portland cement and supplemental cementitious materials, is commonly used to encapsulate the wastes. However, the conventional cementing process based on portland cement has the risk of hydrogen gas generation, due to the radiolysis of the water intrinsically present in the cement matrix both in the pore solution and the hydrated products. The addition of phosphates to calcium aluminate cement (CAC) is interesting because this system sets and hardens via the acid-based reaction, between the acid phosphate solution and the basic CAC cement. Due to this different mechanism of reaction, it would be possible to generate a solid cementitious product with a reduced water content, which can be beneficial to minimize the risk of hydrogen gas generation associated with the radiolysis of water by radioactive wastes. The present study investigates the effect of water reduction on a phosphate modified CAC systems at different temperatures (35C, 60C, 95C, 110C,180C) in the initial 7 days of curing. Experimental results indicate that these phosphate-based cements do not form the conventional CAC crystalline hydration products in the condition tested, but provide a structural integrity despite a significant amount of water loss. The results also suggest the formation of hydroxyapatite in samples cured at 95C.
Garcia-Lodeiro, I.*; Lebon, R.*; Machoney, D.*; Zhang, B.*; Irisawa, Keita; Taniguchi, Takumi; Namiki, Masahiro*; Osugi, Takeshi; Meguro, Yoshihiro; Kinoshita, Hajime*
Proceedings of 3rd International Symposium on Cement-based Materials for Nuclear Wastes (NUWCEM 2018) (USB Flash Drive), 4 Pages, 2018/11
Garcia-Lodeiro, I.*; Irisawa, Keita; Jin, F.*; Meguro, Yoshihiro; Kinoshita, Hajime*
Cement and Concrete Research, 109, p.243 - 253, 2018/07
Times Cited Count：32 Percentile：68.83(Construction & Building Technology)Irisawa, Keita; Taniguchi, Takumi; Namiki, Masahiro; Garc
a-Lodeiro, I.*; Osugi, Takeshi; Sakakibara, Tetsuro; Nakazawa, Osamu; Meguro, Yoshihiro; Kinoshita, Hajime*
Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 6 Pages, 2017/04
A solidification technique with minimized water content is being developed using phosphate cements for the safe storage of secondary radioactive wastes in the Fukushima Daiichi Nuclear Power Plant. Conventional cement systems become solidified via hydration reactions, and need a certain water content. Phosphate cement systems, however, become solidified via an acid-base reaction, and so they only require water mainly for reasons of workability. A reduced water content of phosphate cement systems is beneficial for the immobilization of the radioactive wastes from mitigating the potential to generate hydrogen gas by the radiolysis of water by radioactive wastes. The current study investigated the water content and mineralogy of calcium aluminate cement (CAC) and phosphate-modified CAC (CAP) cured in open systems at 60, 90 and 120 C and in a closed system at 20 C as a reference case. Water contents in both the CAC and the CAP were seen to decrease as curing progressed. For 
90 C, the CAP contained less water than CAC. Free water in CAC converted to structural water by heat treatment, but this was not the case for CAP. An orthophosphate hydrate salt, a precursor phase of hydroxyapatite, was found in CAP when cured at 20 and 60 C, and a mixture of the orthophosphate hydrate salt and hydroxyapatite, Ca
(PO
)
(OH)
, were formed in the CAP when cured at 90 C. Phosphate products in CAP cured at 120 C appears to consist of a different phosphate phase compared with the CAP cured at 20, 60 and 90 C.
Kaminaga, Masanori; Haga, Katsuhiro; Kinoshita, Hidetaka; Terada, Atsuhiko*; Koikegami, Hajime*; Hino, Ryutaro
Proceedings of 11th International Conference on Nuclear Engineering (ICONE-11) (CD-ROM), 7 Pages, 2003/04
1MW pulsed spallation neutron source using a mercury target will be constructed in order to produce high-intensity neutrons for use in the fields of life and material sciences. The mercury target is proposed using a high-energy (3.0GeV) proton beam with a current of 0.333mA and operating at 25 Hz with a pulse duration less than 1
s. A cross flow type (CFT) mercury target has been designed in order to distribute mercury flow according to an axial heat generation distribution caused by spallation reaction, based on the thermal hydraulic analytical results of 3GeV, 1MW proton beam injection by using the STAR-CD code. This paper presents the final CFD analytical results. In the analysis, an inlet temperature of 50C and an inlet mercury velocity of 1.0m/s were assumed. As results, a maximum velocity of 2.48m/s was observed near the front end of the outlet plenum and a maximum of 125.5C was observed near the beam window where the volumetric heat generation rate was relatively large. The maximum temperature is far below the mercury saturation temperature of 356C under atmospheric pressure. This result satisfied the thermal-hydraulic design criteria of "Maximum mercury temperature in the target shall be less than 300C".
Garca-Lodeiro, I.*; Jin, F.*; Irisawa, Keita; Meguro, Yoshihiro; Kinoshita, Hajime*
no journal, ,
Garca-Lodeiro, I.*; Gao, Y.*; Chavda, M.*; Irisawa, Keita; Meguro, Yoshihiro; Kinoshita, Hajime*
no journal, ,
Taniguchi, Takumi; Irisawa, Keita; Ito, Yuzuru; Namiki, Masahiro; Osugi, Takeshi; Abe, Tomohisa; Sato, Junya; Sakakibara, Tetsuro; Nakazawa, Osamu; Meguro, Yoshihiro; et al.
no journal, ,
no abstracts in English
Garca-Lodeiro, I.*; Lebon, R.*; Mahoney, D.*; Zhang, B.*; Irisawa, Keita; Osugi, Takeshi; Nakazawa, Osamu; Kinoshita, Hajime*
no journal, ,
Garca-Lodeiro, I.*; Lebon, R.*; Mahoney, D.*; Zhang, B.*; Irisawa, Keita; Osugi, Takeshi; Nakazawa, Osamu; Kinoshita, Hajime*
no journal, ,
Leaching tests have been conducted on CAC and CAP systems prepared with minimised water content, containing simulated secondary aqueous wastes to investigate their feasibility as wasteforms. In CAC, the effect of reduction in water content on leaching was small whereas CAP system indicated a significant benefit of reduction in water content. CAP appears to be beneficial to retain alkaline earth elements such as Sr, when cured at elevated temperatures.
PO and (NaPO)
as a phosphate source for development of magnesium phosphate cementsGarca-Lodeiro, I.*; Kai Wuen, O.*; Irisawa, Keita; Nakazawa, Osamu; Kinoshita, Hajime*
no journal, ,
Garcia-Lodeiro, I.*; Irisawa, Keita; Lebon, R.*; Mahoney, D.*; Zhang, B.*; Taniguchi, Takumi; Namiki, Masahiro*; Osugi, Takeshi; Meguro, Yoshihiro; Kinoshita, Hajime*
no journal, ,
Irisawa, Keita; Garca-Lodeiro, I.*; Osugi, Takeshi; Nakazawa, Osamu; Meguro, Yoshihiro; Kinoshita, Hajime*
no journal, ,
In order to reduce hydrogen gas explosion and leakage risks for these wastes, we are aiming to develop phosphate cements with minimised water content. The present study investigates roles of phosphate modification on mineral formation in calcium aluminate cement.
Irisawa, Keita; Mcgahan, M.*; Meguro, Yoshihiro; Kinoshita, Hajime*
no journal, ,
Irisawa, Keita; Yeung, S. W.*; Suriwong, P.*; Kinoshita, Hajime*
no journal, ,
In order to evaluate the applicability of calcium aluminate phosphate (CAP) cement as a matrix for nuclear wastes, we investigated the compositional effects on the CAP cement focusing on the caesium incorporation. The CAP samples were prepared by mixing calcium aluminate cement (CAC) with the aqueous solution of (NaPO) and CsNO. CsNO re-precipitated in the conventional CAC sample, suggesting a limited interaction of CAC with CsNO. The increase in the polyphosphate content limited the conventional hydration of CAC and the relative amount of CsNO re-precipitation. This is interesting as it may show a potential interaction between CAP matrix and CsNO.
and ClIrisawa, Keita; Taniguchi, Takumi; Namiki, Masahiro*; Garca-Lodeiro, I.*; Osugi, Takeshi; Nakazawa, Osamu; Kinoshita, Hajime*
no journal, ,
no abstracts in English
