Dissolution kinetics of pyrochlore ceramics for the disposition of plutonium
ABSTRACT Single-pass flow-through experiments were conducted on a set of non-radioactive TiO2-based ceramics at 90°C and pH = 2 to 12. The specimens contained 27.9 to 35.8 mass% CeO2 as a surrogate for UO2 and PuO2. Pyrochlore and Hf-rutile and pyrochlore, zirconolite, and Hf-rutile constituted the major phases in the “pure phase” pyrochlore and pyrochlore-baseline ceramics, respectively. Results from dissolution experiments between pH = 2 to 12 indicate a shallow pH-dependence with an ill-defined minimum. Element release rates determined from experiments over a range of sample surface areas (S) and flow rates (q) indicate that dissolution rates become independent of q/S values at 10-8 to 10-7 m•s-1. Dissolution rates dropped sharply at lower values of q/S, indicating rates that are subject to solution saturation effects as dissolved constituents become concentrated. Forward dissolution rates were 1.25•10-3 (±0.299) and 5.54•10-3 (±1.26) (esd) g/(m2•d) for “pure phase” pyrochlore and pyrochlore-baseline ceramics, respectively. Dissolution rates obtained in other laboratories compare well to the findings of this study, once the rate data are placed in the context of solution saturation state. These results make progress towards an evaluation of CeO2 as a surrogate for UO2 and PuO2 as well as establishing a baseline for comparison with radiation-damaged specimens.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 876844
- Report Number(s):
- PNNL-SA-47458; AMMIAY; NN6001020; TRN: US0601450
- Journal Information:
- American Mineralogist, 91(1):39-53, Vol. 91, Issue 1; ISSN 0003-004X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
DISSOLUTION
CHEMICAL REACTION KINETICS
PLUTONIUM OXIDES
PYROCHLORE
ZIRCONOLITE
TITANIUM OXIDES
CERIUM OXIDES
URANIUM OXIDES
PHASE STUDIES
WASTE FORMS
Pyrochlore
dissolution
kinetics
experimental