Hydrothermal interaction of solid wafers of Topopah Spring Tuff with J-13 water and distilled water at 90, 150, and 250{sup 0}C, using Dickson-type, gold-bag rocking autoclaves

The Nevada Nuclear Waste Storage Investigations Project has conducted experiments to study the hydrothermal interaction of rock and water representative of a potential high-level waste repository at Yucca Mountain, Nevada. The results of these experiments help define the near-field repository environment during and shortly after the thermal period that results from the emplacement of nuclear waste. When considered in conjunction with results contained in companion reports, these results can be used to assess our ability to accelerate tests using the surface area/volume parameter and/or temperature. These rock-water interaction experiments were conducted with solid polished wafers cut from both drillcore and outcrop samples of Topopah tuff, using both a natural ground water and distilled water as the reacting fluid. Pre- and post-test characterization of the reacting materials was extensive. Post-test identification and chemical analysis of secondary phases resulting from the hydrothermal interactions were aided by using monoliths of tuff rather than crushed material. All experiments were run in Dickson-type, gold-bag rocking autoclaves that were periodically sampled at in situ conditions. A total of nine short-term (up to 66-day) experiments were run in this series; these experiments covered the range from 90 to 250{sup 0}C and from 50 to 100 bar. The results obtained from the experiments have been used to evaluate the modeled results produced by calculations using the geochemical reaction process code EQ3/6. 31 refs., 37 figs., 7 tabs.