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Optimization of sintered AgI-mordenite composites for129I storage

International Nuclear Fuel Cycle Conference, GLOBAL 2013: Nuclear Energy at a Crossroads

Garino, Terry J.; Nenoff, Tina M.; Rodriguez, Mark A.; Mowry, Curtis D.; Rademacher, David X.

The thermal processing of a proposed durable waste form for 129I was investigated. The waste form is a composite with a matrix of low-temperature sintering glass that encapsulates particles of AgI-mordenite. Ag-mordenite, an ion-exchanged zeolite, is being considered as a capture medium for gaseous 129I2 as part of a spent nuclear fuel reprocessing scheme under development by the US Department of Energy/Nuclear Energy (NE). The thermal processing of the waste form is necessary to densify the glass matrix by viscous sintering so that the final waste form does not have any open porosity. Other processes that can also occur during the thermal treatment include desorption of chemisorbed I2, volatilization of AgI and crystallization of the glass matrix. We have optimized the thermal processing to achieve the desired high density with higher AgI-mordenite loading levels and with minimal loss of iodine. Using these conditions, 625°C for 20 minutes, the matrix crystallizes to form a eulytite phase. Results of durability tests indicate that the matrix crystallization does not significantly decrease the durability in aqueous environments.

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TYPE Conference YEAR 2013
OSTIScopus

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

Journal of Chemical Physics

Leung, Kevin; Nenoff, Tina 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
Results 251–275 of 357
Results 251–275 of 357