Application of phosphate modified CAC for incorporation of simulated secondary aqueous wastes in Fukushima Daiichi NPP, 1; Characterization of solidified cementitious systems with reduced water content

Garcia-Lodeiro, I.*; Lebon, R.*; Machoney, D.*; Zhang, B.*; Irisawa, Keita  ; Taniguchi, Takumi ; Namiki, Masahiro*; Osugi, Takeshi  ; Meguro, Yoshihiro  ; Kinoshita, Hajime*

Processing of contaminated water from Fukushima Daiichi Nuclear Power Plant (NPP) results in a large amount of radioactive aqueous wastes, with a significant amount of radioactive strontium (Sr) and inorganic salts (mainly chlorides). It is challenging to condition these wastes using the conventional cementation because of the significant contamination and associated risk of hydrogen gas generation. The present study investigates the applicability of calcium aluminate cement (CAC) modified with phosphates (CAP) for incorporation of simulated secondary aqueous wastes. The use of CAP system is interesting because it may allow the reduction of water content, and the risk of hydrogen gas generation, since the solidification of this systems does not solely rely on the hydration of clinker phases. CAC and CAP pastes were prepared intermixing with different secondary aqueous wastes (concentrated effluent, iron co-precipitation slurry and carbonate slurry) and cured at either 35C or 90C in open systems for 7 days. Overall, the incorporation of the simulated wastes did not significantly alter the development of CAP or CAC, maintaining the integrity of their microstructure. However, because of the high Cl content in the simulated wastes, CAC system showed formation of the Friedel's salt (CaAl(OH)Cl(HO)). On the other hand, formation of chlorapatite-type phase was detected in the CAP systems cured at 90C.