Evaporative chemical evolution of natural waters at Yucca Mountain, Nevada

The authors report results from experiments on the evaporative chemical evo lution of the two major types of natural waters present at Yucca Mountain, Nevada. The first is represented by J13 well water, a dilute Na-HCO3-CO3 wa ter similar to saturated horizons in volcanic tuffs across the western Unit ed States. The second is represented by Ca-Cl-SO4-rich pore water that has a higher dissolved ion content, from the unsaturated zone above the reposit ory horizon. Data include anion and cation analysis and qualitative mineral identification for a series of open system experiments, with and without c rushed tuff present, conducted at sub-boiling temperatures (75-85 degreesC) . This work is motivated by a need to characterize the chemistry of concent rated aqueous films that might form on engineered components at the potenti al high-level, nuclear-waste repository at Yucca Mountain, Nevada and lead to electrochemical corrosion. The experiments indicate the evolution of hig h pH, Na-HCO3-CO3 brines from J13-like waters and the evolution of near neu tral pH brines from the pore water compositions. The minerals recovered aft er complete evaporation of the J13 water alone experiments include amorphou s silica, aragonite, calcite, halite, niter, thermonatrite and, possibly, g ypsum, anhydrite and hectorite. Tachyhydrite and gypsum were observed to fo rm in equivalent experiments with pore waters from the unsaturated zone. (C ) 2001 Elsevier Science Ltd. All rights reserved.