Modeling of Radiation Effects on the Chemical Durability of Nuclear Waste Forms (Leaching, Radioactive Glass Damage)
Ougouag, Abderrafi Mohammed El Amine
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https://hdl.handle.net/2142/70899
Description
Title
Modeling of Radiation Effects on the Chemical Durability of Nuclear Waste Forms (Leaching, Radioactive Glass Damage)
Author(s)
Ougouag, Abderrafi Mohammed El Amine
Issue Date
1984
Department of Study
Nuclear Engineering
Discipline
Nuclear Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Nuclear
Abstract
In solidified forms incorporating high level nuclear waste, the long-term effects of radiation on chemical durability are attributed to the accumulation of atomic displacements; the latter are caused mainly by the recoiling nuclei, or (alpha)-recoils, accompanying the emission of (alpha)-particles resulting from the presence of actinides in the waste. Two techniques, actinide doping and ion implantation, have been preferentially used to study the effects of (alpha)-decay aging on the leachability of waste forms. Some of the results obtained by ion implantation have negative implications about the long-term durability of glassified forms; these results, however, have not been supported by those obtained by actinide doping. In this work, an attempt has been made to interpret and reconcile the results yielded by the two accelerated radiation-aging techniques, in order to better predict the long-term effects of radiation on the leachability of actual nuclear waste glasses. As a starting point, it is assumed that the implanted ions and (alpha)-recoils register latent tracks that etch faster than the surrounding undamaged waste form. This model allows the successful interpretation of the leaching trends observed when ion-implanted specimens are exposed to aqueous solutions. However, the model predicts similar trends for the actinide-doped specimens even when the differences between the two techniques with regard to geometry and statistics applicable to the distribution of damage are taken into account. Therefore, to explain the different results yielded by the two approaches, other specific phenomena induced by the respective experimental conditions have to be considered. Two of those have been retained: (i) the differences in the kinetics governing the accumulation of reactive defects, and (ii) the dissimilarities in stress buildup in the irradiated specimens. Accounting for the differences in the kinetics of damage ingrowth arising from the much higher dose rates realized in ion implantation experiments, leads to predicted trends that are physically correct at low and high fluxes and fluences. Differences in stress buildup are shown to arise from the dissimilarity in directionality between the two irradiation techniques. The predicted buildup and release of stress accurately reproduce the experimental results. From this study, it is concluded that the occurrence of sudden increase in dissolution rates observed from some ion-implanted glasses do not imply similar increases for actual waste glasses contacted by ground water.
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