Hydrothermal interaction of Topopah Spring tuff with J-13 water as a function of temperature

In support of the Nevada Nuclear Waste Storage Investigations Project experiments were conducted to study the hydrothermal interaction of rock and representative of a potential repository in tuff. These experiments provided data relevant to near-field repository conditions that can be used to: assess the ability to use ''accelerated'' tests based on the SA/V (surface area/volume) parameter and temperature; allow the measurement of chemical changes in phases present in the tuff before reaction as well as the identification and chemical analysis of secondary phases resulting from hydrothermal reactions; and demonstrate the usefulness of geochemical modeling in a repository environment using the EQ3/6 thermodynamic/kinetic geochemical modeling code. Crushed tuff and polished wafers of tuff were reacted with a natural ground water in Dickson-type gold-cell rocking autoclaves which were periodically sampled under insitu conditions. Results were compared with predictions based on the EQ3/6 geochemical modeling code. Eight short-term experiments ( 2 to 3 months) at 1500C and 2500C have been completed using tuff from both drillcore and outcrop. Long-term experiments at 900C and 1500C using drillcore polished wafers are in progress. This paper will focus on the results of the 1500C and 2500C experiments using drillcore polished wafers. 11 refs., 4 figs