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The Crystalline-Amorphous Transformation in Natural Zirconolite: Evidence for Long-Term Annealing

Published online by Cambridge University Press:  10 February 2011

Gregory R. Lumpkin
Affiliation:
Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234, Australia
Katherine L. Smith
Affiliation:
Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234, Australia
Mark G. Blackford
Affiliation:
Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234, Australia
Reto Gieré
Affiliation:
Dept. of Earth and Atmospheric Sciences, Purdue Univ., West Lafayette, IN 47907-1397, USA
C. Terry Williams
Affiliation:
Dept. of Mineralogy, The Natural History Museum, Cromwell Rd., London SW7 5BD, UK
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Abstract

Dose-age relationships have been determined by analytical and transmission electron microscopy (AEM and TEM) for the onset dose and critical amorphization dose of a suite of natural zirconolites. Together with a preliminary investigation of the thermal histories of the zirconolite-bearing rocks, the results indicate that valid estimates of D0 (intercept dose at t = 0) and K (annealing rate constant) are obtained and that the host rocks experienced temperatures on the order of 100-200 °C averaged over time. The natural samples are therefore best suited as radiation damage analogues for waste forms stored under deep borehole conditions where temperatures of 100-450 °C are expected. Our results indicate that the critical amorphization (or saturation) dose of zirconolite will increase by a factor of approximately 2 or more as a result of storage at elevated temperature. The effect of long-term annealing on the critical amorphization dose is only important for times in excess of 107-108 years due to the low annealing rate constant of 10−9/yr.

Type
Research Article
Copyright
Copyright © Materials Research Society 1998

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