Development of stable solidification technique of ALPS sediment wastes by apatite ceramics (Contract research); FY2020 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Tokyo Institute of Technology*

JAEA-Review 2021-077, 217 Pages, 2022/03

JAEA-Review-2021-077.pdf:12.34MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2020. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2019, this report summarizes the research results of the "Development of stable solidification technique of ALPS sediment wastes by apatite ceramics" conducted in FY2020. The present study aims to establish an apatite solidification process of radioactive sediment wastes, which were generated from the ALPS process manipulating the large amount of contaminated water from Fukushima Daiichi Nuclear Power Station. In FY2020, the synthetic scheme and elemental composition were updated to precipitation method to accept the actual ALPS sediment wastes in engineering scale. The synthesis of apatite or phosphate wastes and their molding conditions were surveyed, and the relations among elemental compositions, structures and chemical properties were clarified.

Development of phosphate modified CAC cementitious systems with reduced water content for the immobilization of radioactive wastes

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.

Heat treatment of phosphate-modified cementitious matrices for safe storage of secondary radioactive aqueous wastes in Fukushima Daiichi Nuclear Power Plant

Irisawa, Keita; Taniguchi, Takumi; Namiki, Masahiro; Garca-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.

Uptake of cadmium by synthetic mica and apatite; Observation by micro-PIXE

Kozai, Naofumi; Onuki, Toshihiko; Komarneni, S.*; Kamiya, Tomihiro; Sakai, Takuro; Oikawa, Masakazu*; Sato, Takahiro

Nuclear Instruments and Methods in Physics Research B, 210, p.513 - 518, 2003/09

https://doi.org/10.1016/S0168-583X(03)01088-7

This study examined removal of cadmium from solution by two materials with high sorptivity for cadmium: a synthetic mica named Na-4 mica and an apatite. At an initial Cd concentration of 110M and a starting pH of 3, the distribution coefficient of Na-4 mica for Cd (8.410ml/g) was one order of mgnitude of higher than that of apatite (8.210ml/g). On the other thand, micro-PIXE anaysis for a mixture of equal mass of Na-4 mica and apatite contacted with Cd solution under the same conditions revealed that Cd was selectively taken up by the apatite in the mixture, while Cd was not detected on the Na-4 mica in the mixture. This result by micro-PIXE analysis is not what is expected from the above distribution coefficient values of Na-4 mica and apatite. This result can be explained by irreversibility of the uptake and the difference in kinetics of the uptake by the Na-4 mica and apatite.

Development of solidification techniques with minimised water content for secondary radioactive aqueous wastes in Fukushima, 3; Effects of phosphates on calcium aluminate cement under hydrothermal conditions

Garca-Lodeiro, I.*; Gao, Y.*; Chavda, M.*; Irisawa, Keita; Meguro, Yoshihiro; Kinoshita, Hajime*

no journal, ,