Prediction of thermodynamic property of Pu-zircon and Pu-pyrochlore

Xu, Hulfang; Wang, Yifeng
July 2000
AIP Conference Proceedings;2000, Vol. 532 Issue 1, p363
Academic Journal
Due to its high durability, zircon is often present as a heavy mineral in natural environments and is the oldest mineral that has been dated on the earth. There are four zircon structure phases of M[sup 4+]SiO[sub 4] occurring in nature: zircon (ZrSiO[sub 4]), hafnon (HfSiO[sub 4]), thorite (ThSiO[sub 4]), and coffinite (USiO[sub 4]). These phases may form solid solution. Recent interest in zircon minerals stems from the study of highly durable radioactive waste forms. Crystalline phases of M[sup 4+]SiO[sub 4] with zircon structure have been proposed as a durable ceramic waste form for immobilizing actinides such as Pu, Np, and U. To predict the behavior of zircon-based waste forms in a geologic repository environment as well as to optimize the fabrication of those waste forms, the thermodynamic and kinetic properties for zircon mineral phases have to be determined. In this paper, we use a linear free energy relationship to predict the Gibbs free energies of formation of Pu-bearing phases (Xu et al., 1999). The calculated results show that the PuSiO[sub 4] phase with zircon structure is unstable with respect to oxides of PuO[sub 2] and quartz. However, the PuSiO[sub 4] phase will be stable with respect to oxides of PuO[sub 2] and silica glass at low temperature. © 2000 American Institute of Physics.


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