Basalt glass: an analogue for the evaluation of the long-term stability of nuclear waste form borosilicate glasses

Abstract

The long-term stability of nuclear waste form borosilicate glasses can be evaluated by understanding the processes that effect the long-term alteration of glass and by comparing laboratory alteration of synthetic basalt and borosilicate glasses with the observed stability of naturally occurring basaltic glasses in diverse geologic environments. This paper presents detailed electron microprobe analyses of naturally altered basaltic glasses (with maxi mum ages of 10,000 to 20 million years) from low-temperature environments. These results are compared to laboratory data on the corrosion of a synthetic basaltic glass in MCC-1 tests (90*C, a SA/V of 0.1 cm" 1 and time periods up to 182 days), MCC-2 tests (190 o C, a SA/V of 0.1 cm" 1 and time periods up to 210 days) and hydration tests in saturated water vapor (2-in°C , an es.tima.ted SA/V of-U06 cm" 1 and time periods up to 63 days). /uditionally, laboratory induced hydration alteration of synthetic basalt and borosilicate glasses is compared. These preliminary experiments provide evidence that the alteration processes observed for natural basalt glasses are relevant to understanding the alteration of nuclear waste glass, as both appear to react via similar processes.

Natural Glasses

“…Therefore, in the last decades many studies have been devoted to get information from natural analogues, in order to corroborate predictive models of the long-term processes which affect the stability of radioactive waste repositories, since they provide the opportunity to examine processes occurring over geological timescales (natural basalt provide data on the alteration behavior of amorphous materials over tens or hundreds of thousands years) (e.g. [35][36][37][38]).…”

“…Byers et al [37] reported that the alteration of basalt glasses in nature is driven by a hydrolytic dissolution/re-precipitation mechanism which results in the formation of welldefined iron-rich aluminosilicate surface layers (palagonite). Natural glass alteration is also accompanied by the precipitation of authigenic cements (e.g., zeolites, clay minerals), and the clay mineralization observed on natural glasses is very similar to that produced on laboratory altered glasses [39,40].…”

Basaltic dykes in evaporites: a natural analogue

“…Several studies have shown that similar alteration products form on both nuclear waste and natural glasses in spite of differences in the chemical composition between natural basalt and synthetic HLW borosilicate glass (Malow et al 1984;Byers et al 1985;Crovisier et al 1992;Lutze & Grambow 1992;Petit 1992;Abdelouas et al 1994;Daux et al 1997).…”