[en] Simulated spent fuel, simulated defense high-level waste, and simulated and ⁹⁹Tc-doped commercial high-level waste (PNL 76-68) were reacted with groundwater, both in the presence and absence of basalt, simulating expected conditions for a nuclear waste repository located in basalt in gold bag sampling autoclaves at temperatures between 90⁰ and 300⁰C, at 30 MPa pressure. During the course of the experiments, samples of the fluid phase were periodically withdrawn from the autoclaves and were analyzed for pH as well as major, minor, and trace cations and anions. At 200 and 300⁰C, all dissolved species displayed either steady-state concentrations or decreasing concentrations after the first 1000 h. At 100⁰C, some dissolved components had not reached steady-state concentrations after 6000 h. Solids characterization suggests that the formation of secondary alteration phases such as alkali feldspar, smectite clays, scapolite, and a variety of uranium-bearing silicate phases, imposes solubility limits on the release of many analog elements of potential radionuclides. These steady-state (or solubility) concentration limits can be coupled with measured hydrologic flow rates to calculate radionuclide release rates from the waste form for a nuclear waste repository in basalt. The experimentally determined steady-state concentrations of analog elements are compared to calculated solubilities for individual elements. In many cases, the experimentally determined concentrations are several orders of magnitude higher than the calculated solubility concentrations. Possible reasons for these discrepancies include invalid assumptions on stable alteration solids, temperature differences, and kinetic effects. The steady-state concentrations reported in this document provide realistic and defensibly conservative data that can be used on a preliminary basis for evaluating waste form performance both alone and in the presence of basalt