Hydrothermal Interaction of Topopah Spring Tuff With J-13 Water as a Function of Temperature

Abstract

AbstractIn support of the Nevada Nuclear Waste Storage Investigations Project experiments were conducted to study the hydrothermal interaction of rock and water 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 150°C and 250°C have been completed using tuff from both drillcore and outcrop. Long-term experiments at 90°C and 150°C using drillcore polished wafers are in progress. This paper will focus on the results of the 150°C and 250°C experiments using drillcore polished wafers.