Comparison of experimental and model data for the evaporation of a synthetic Topopah Spring Tuff pore water, Yucca Mountain, USA

摘要

We evaporated a synthetic Topopah Spring Tuff water representative of one type of pore water at Yucca Mountain, NV to determine the chemical controls on brine compositions that may contact the engineered barrier-system component (waste package and drip shield) surfaces at the designated high-level radioactive waste repository. At 95°C, the dilute water evolved towards a concentrated brine that contained about 45 mol% Cl, 7 mol% NO_3, 43 mol% Na, 4 mol% K, and less than 1 mol% each of SO_4, Ca, Mg, HCO_3, F, and Si. All measured ions in the condensed vapor were below detection limit, indicating no gas volatilization at these conditions. Geochemical modeling of the solution chemistry and identification of solids suggest that fluorite, bassanite (or other calcium sulfates), pentasalt, sepiolite (or an amorphous Mg-silicate) and halite are the principle chemical controls on the composition of "sulfate" brines. Corrosiveness of these waters will be minimized by the precipitation of F, Ca, and Mg during evaporation.