Thermal Stability of Zeolitic Tuff from Yucca Mountain, Nevada

Bish, David L.; ,

Thermal Stability of Zeolitic Tuff from Yucca Mountain, Nevada

by David L. Bish, Los Alamos Natl Lab, United States,

Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1990

Abstract:

Thermal models of the potential repository at Yucca Mountain, Nevada, suggest that rocks near the potential host rock will experience elevated temperatures for at least 1000 yr. In order to assess the effects of elevated temperatures on zeolitic tuffs, the thermal stabilities of the zeolites clinoptilolite and mordenite, common in the rocks at Yucca Mountain, were investigated using a combination of high-temperature X-ray powder diffraction, thermogravimetric and differential scanning calorimetric analysis, and long-term heating experiments. Clinoptilolite undergoes an anisotropic decrease in volume upon heating or dehydration, accompanied by evolution of water. Mordenite experiences a relatively minor decrease in volume, accompanied by evolution of water. The details of the thermal behavior of both zeolites are dependent on exchangeable cation composition and the water fugacity of the environment. Long-term (years) heating to 200?C causes irreversible collapse of the clinoptilolite structure that is also composition dependent; sorptive properties are only slightly affected.

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