Journal of the Ceramic Society of Japan
Online ISSN : 1348-6535
Print ISSN : 1882-0743
ISSN-L : 1348-6535
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Crystallization of molybdenum oxide phase from simulated high-level waste glass under slow cooling
Toru SugawaraToshiaki OhiraAyaka SekineMaki AdachiHitomi Sato
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2022 Volume 130 Issue 12 Pages 933-942


In the vitrification of high-level radioactive waste, it is important to understand the crystallization behavior because precipitation of molybdenum (Mo) phase reduces the chemical durability of the waste form. In this study, the crystallization of Mo phase under slow cooling conditions was investigated with glasses of SiO2–B2O3–Al2O3–CaO–Na2O–MoO3 systems and simulated high-level waste (HLW) compositions. When the B2O3 in the glass decreases and the Al2O3 increases, the phase separation of Na2MoO4 and the crystallization of powellite (CaMoO4) were promoted. The waste components included in the HLW glass has the effect of increasing the MoO3 solubility and suppressing crystallization. Furthermore, it was found that the suppressing effect was further enhanced by addition of rare earth element oxides. In contrast, there was no suppressing effect of addition of V2O5 on the crystallization of powellite. The precipitation of the Na2MoO4 is mainly related to liquid-liquid immiscibility, while the crystallization of powellite depends on the multiple factors, an equilibrium MoO3 solubility at high temperature, nucleation and growth rates under slow-cooling and crystallization of Ca-silicate phase. The compositional effects on the crystallization can be described using the melt viscosity.

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