Prediction of the long-term performance of crystalline nuclear waste form phases from studies of mineral analogues

Lumpkin, GR; Smith, KL; Blackford, MG; McGlinn, PJ; Gieré, R; Williams, CT

Prediction of the long-term performance of crystalline nuclear waste form phases from studies of mineral analogues

Date

1994-05-01

Authors

Publisher

Institution of Engineers, Australia

Abstract

This investigation outlines the use of natural analogues as a means of assessing the long-term performance of actinide host phases in crystalline nuclear waste forms. We employed several analytical techniques to study the mineral zirconolite, an important actinide host phase in Synroc and tailored ceramics. The following conclusions were reached: 1) Natural zirconolite experiences a crystalline to aperiodic transformation at doses of approximately 10 to 10 alpha/mg (0.08-1.0 dpa), consistent with the results of accelerated damage testing on synthetic zirconolite. 2) Damage microstructures are consistent with the accumulation and overlap of alpha-recoil collision cascades, resulting in aperiodic domains which increase in volume as a function of dose. 3) There is evidence for long-term annealing of alpha-recoil damage in zirconolite at a rate 2-5 times slower than in the structurally related mineral pyrochlore. 4) Analysis of data from the only documented natural zirconolites to show hydrothermal alteration [resulting from F- and P-rich aqueous fluids at T = 500-600 degrees C and P = 2 kb, Giere and Williams (14)], suggests that Th and U were released to the fluid phase. 5) The effects of low temperature alteration of radiation damaged zirconolite by a Si-rich ground water or fluid phase were identified in the oldest (2.5 x 10 yr) sample in our research collection. Alteration involved incorporation of Si along microfractures at the expense of Ca, Ti, and Fe, but Th and U remained immobile. In this same sample, there is evidence for migration of at least 50% of the radiogenic Pb from both unaltered and altered areas of zirconolite. Most of the Pb may have been retained within the sample as fine precipitates of galena (PbS).

Keywords

Actinides, Ground water, Radioactive wastes, Zirconolite, Crystals, Waste forms, Minerals, Synthetic rocks

Citation

Lumpkin, G. R., Smith, K. L., Blackford, M. G., McGlinn, P., Giere, R., & Williams, C. T. (1994). Prediction of the long-term performance of crystalline nuclear waste form phases from studies of mineral analogues. In Proceedings, 9th Pacific Basin Nuclear Conference: Nuclear energy, science and technology Pacific partnership, Sydney, Australia, 1-6 May 1994, (pp. 879-885). Barton, ACT: Institution of Engineers, Australia.