Temporal variations of aqueous constituents in a water-basalt-supercalcine system: implications for the experimental assessment of nuclear waste forms

A Dickson-type rocking autoclave has been used for studying the interaction of a synthetic groundwater solution with the non-radioactive simulated nuclear-waste form supercalcine (SPC-4), and with a mixture of supercalcine plus basalt, at 300 deg and 200 deg C at 300 bars. Over the course of a month, the concentrations of the aqueous species of Mo, Na, Si, K, Rb, Al, Cr, and H+ displayed rapid change initially followed by a gradual approach to constant or nearly constant values, whereas the solids displayed very little alteration. These observations suggest that dissolution/precipitation reactions are quickly established even though the solids are very sluggish in attaining a completely altered or equilibrium state. The effects of various waste-form crystallinities and material preparations on the solution chemistry are quite different, but reproducible, and are discussed in terms of assessing potential waste forms. (author)