ABSTRACT. A borosilicate glass, containing 25 wt. % of simulated high-level radioactive waste has been reacted with water at 350 ~ and 500 bars for 14 and 48 days using large-volume 'cold-seal' high-pressure equipment. Under these conditions the glass crystallizes a suite of mineral phases including: albite, NaA1Si3Os; aegirine, NaFeSi206; riebeckite, Na2Fez(Fe,Mg)aSisOE2(OH)2; zektzerite, LiNaZrSirOls; barium strontium molybdate, (Ba,Sr) MOO4; stillwellite, (Nd,Ce,La)BSiOs; willemite, ZnzSiO4; smectite; a lithium-sodium borosilicate hydrate; melilite (fikermanite), Ca2MgSi20 7. A description of the morphology of these phases is given, together with a number of chemical analyses. The implications of the incorporation of waste species in these mineral phases to the disposal of high-level radioactive waste is discussed. K E V W O R D S:radioactive waste, borosilicate glass, albite, aegirine, riebeckite, zektzerite, stillwellite, willemite, smectite, melilite.
An essential component of any assessment of HLRW geological disposal options is the quantitative prediction of radionuclide release rates from the near-field over time spans of the order of 103-106 years. Fundamental to this assessment is the investigation of the interaction of potential wasteforms with groundwater under repository conditions of temperature, pressure, and groundwater flow-rate. Consequently, many studies world-wide have been initiated to examine the kinetics of wasteform dissolution over a wide range of physical and chemical conditions. Although these studies have provided a considerable amount of invaluable data on wasteform-fluid interactions, they have tended to focus on breakdown of the wasteform itself, and not on the fate of released waste components in the nearfield. For example, effects of saturation of species in solution, precipitation of secondary minerals or amorphous gels, and the effect of host rock chemistry on the products (solid and fluid) of waste-fluid interaction have largely been ignored or even specifically excluded in laboratory experiments. This is despite growing evidence from source term modelling studies which suggest that the above processes may well be the chief factors in governing rates of radionuclide release from the near-field, bearing in mind the limited availability of ground
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