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Hydration structures of U(III) and U(IV) ions from ab initio molecular dynamics simulations

Journal of Chemical Physics

Leung, Kevin L.; Nenoff, T.M.

We apply DFTU-based ab initio molecular dynamics simulations to study the hydration structures of U(III) and U(IV) ions, pertinent to redox reactions associated with uranium salts in aqueous media. U(III) is predicted to be coordinated to 8 water molecules, while U(IV) has a hydration number between 7 and 8. At least one of the innershell water molecules of the hydrated U(IV) complex becomes spontaneously deprotonated. As a result, the U(IV)-O pair correlation function exhibits a satellite peak at 2.15 Å associated with the shorter U(IV)-(OH -) bond. This feature is not accounted for in analysis of extended x-ray absorption fine structure and x-ray adsorption near edge structure measurements, which yield higher estimates of U(IV) hydration numbers. This suggests that it may be useful to include the effect of possible hydrolysis in future interpretation of experiments, especially when the experimental pH is close to the reported hydrolysis equilibrium constant value. © 2012 American Institute of Physics.

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TYPE Journal Article YEAR 2012
DOIOSTIScopus

Low-temperature sintering Bi-Si-Zn-oxide glasses for use in either glass composite materials or core/shell 129I waste forms

Journal of the American Ceramic Society

Garino, Terry J.; Nenoff, T.M.; Krumhansl, James L.; Rademacher, David R.

Spent nuclear fuel contains 129I, which is of particular concern due to its very long half-life, its potential mobility in the environment, and its deleterious effect on human health. In spent fuel reprocessing schemes under consideration, a gas stream containing 129I2 would be passed through a bed of Ag-loaded zeolites such as Ag-mordenite (Ag-MOR). We have investigated the use of a low-temperature sintering bismuth-silicon-zinc- oxide glass powder mixed with either AgI or AgI-MOR to produce dense glass composite material waste forms that can be processed at 550°C, where AgI volatility is low. We have demonstrated that when fine silver flake is added to the mixture, any adsorbed I2 released during heating of AgI-MOR reacts with the silver to form AgI in situ. Furthermore, we have shown that mixtures of the glass with the AgI-MOR or AgI are durable in aqueous environments. Finally, we have developed a process to fabricate core/shell waste forms where the core of AgI-MOR or AgI and glass is encased in a shell of glass that protects the core from contact with the environment. To prevent cracking of the shell due to thermal expansion mismatch between the core and shell, amorphous silica was added to the shell to form a composite with a lower coefficient of thermal expansion. © 2011 The American Ceramic Society.

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TYPE Journal Article YEAR 2011
OSTIScopus
Results 251–275 of 347
Results 251–275 of 347