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Alpha-Recoil Effect on the Dissolution of Betafite: Rapid Natural Annealing of Radiation Damage Within A Metamict Phase

Published online by Cambridge University Press:  28 February 2011

Y. Eyal ,
G. R. Lumpkin  and
R. C. Ewing
Y. Eyal
Affiliation:
Department of Nuclear Engineering, Technion - Israel Institute of Technology, Haifa 32000, Israel
G. R. Lumpkin
Affiliation:
Department of Geology, University of New Mexico, Albuquerque, New Mexico 87131, USA
R. C. Ewing
Affiliation:
Department of Geology, University of New Mexico, Albuquerque, New Mexico 87131, USA
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Abstract

Betafite, a radioactive mineral, is the Ti-rich member of the pyrochlore group, A1–2B2X6Y0–1, (Fd3m, Z = 8), where A = Ca, Na, U, Th, REE (rare earth elements), Y, Ba, Sr, Bi, Pb; B = Nb, Ti, Ta, Zr, Sn, Fe: X = oxygen; Y = 0, OH and F. The pyrochlore structure (or structural derivatives, e.g. zirconolite in SYNROC) is a common constituent of polyphase, crystalline radioactive waste forms. Naturally occurring minerals with this structure often occur in the metamict state. Therefore, a principal concern is the effect of alpha-recoil damage on the structure and dissolution behavior of synthetic, analogue, waste-form phases which contain actinides.

We describe the dissolution behavior of 238U, 234U, 232Th, 230Th and 228Th in betafite during leaching in a bicarbonate-carbonate solution. Results indicate enhanced leaching of recently produced alpha-recoil damage as evidenced by the more rapid dissolution rate of 228Th relative to 232Th and 230Th, and only slightly enhanced leaching of older damage as evidenced by a small increase in the dissolution rate of 234U relative to 238U. These experiments demonstrate that individual alpha-recoil tracks are preserved for some time as disordered regions of higher chemical reactivity in already fully-damaged, aperiodic structures. We estimate an annealing time for the alpha-recoil tracks of 2,000 ± 1,300 yr in the metastable, aperiodic structure. Similar alpha-recoil tracks should be formed and annealed in other aperiodic nuclear waste forms, such as borosilicate glass.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 50: Symposium STOCKHOLM – Scientific Basis for Nuclear Waste Management IX , 1985 , 379
Copyright
Copyright © Materials Research Society 1985

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References

1. Lumpkin, G. R. and Ewing, R. C., in Scientific Basis for Nuclear Waste Management VIII, edited by Jantzen, M., Stone, J. A. and Ewing, R. C. (Materials Research Society, Pittsburgh, 1985) pp. 647–654.Google Scholar
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