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Oxidative Alteration of Spent Fuel in a Silica-Rich Environment: SEM/AEM Investigation and Geochemical Modeling

Published online by Cambridge University Press:  10 February 2011

Yifeng Wang  and
Huifang Xu
Yifeng Wang
Affiliation:
Sandia National Laboratories, 4100 National Parks Highway, Carlsbad, New Mexico88220. E-mail: ywang@sandia.gov
Huifang Xu
Affiliation:
Department of Earth and Planetary Sciences, The University of New Mexico, Albuquerque, New Mexico87131. E-mail: hfxu@unm.edu
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Abstract

Correctly identifying the possible alteration products and accurately predicting their occurrence in a repository-relevant environment are the key for source-term calculations in a repository performance assessment. Uraninite in uranium deposits has long been used as a natural analog to spent fuel in a repository because of their chemical and structural similarity. In this paper, a SEM/AEM investigation has been conducted on a partially alterated uraninite sample from a uranium ore deposit of Shinkolobwe of Congo. The mineral formation sequences were identified: uraninite → uranyl hydrates → uranyl silicates → Ca-uranyl silicates or uraninite → uranyl silicates → Ca-uranyl silicates. Reaction-path calculations were conducted for the oxidative dissolution of spent fuel in a representative Yucca Mountain groundwater. The predicted sequence is in general consistent with the SEM observations. The calculations also show that uranium carbonate minerals are unlikely to become major solubility-controlling mineral phases in a Yucca Mountain environment. Some discrepancies between model predictions and field observations are observed. Those discrepancies may result from poorly constrained thermodynamic data for uranyl silicate minerals.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 608: Symposium QQ – Scientific Basis for Nuclear Waste Management XXIII , 1999 , 67
Copyright
Copyright © Materials Research Society 2000

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References

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