Zeolite stability constraints on radioactive waste isolation in zeolite-bearing volcanic rocks
Silicic tuffs of the southern Great Basin and basalts of the Columbia River Plateau are under investigation as potential host rocks for high- and intermediate-level radioactive wastes. Non-welded and partially welded tuffs may contain major amounts (> 50%) of the zeolite minerals: clinoptilolite, mordenite, and analcime. Densely welded tuffs and some basalt flows may contain clinoptilolite as fracture filling which limits permeability of these rocks. The cation exchange properties of these zeolite minerals allow them to pose a natural barrier to the migration of cationic species of various radionuclides in aqueous solutions. However, these minerals are unstable at elevated temperatures and at low water vapor pressures, and they may break down either by reversible dehydration or by irreversible mineralogical reactions. All of the breakdown reactions occurring with increased temperature involve a net volume reduction and evolution of fluids. Thus, they may provide both a pathway (shrinkage fractures) and a driving force (fluid pressure) for release of radionuclides to the biosphere. These reactions may be avoided by keeping zeolite-bearing horizons saturated with water and below about 85{sup 0}C. This may restrict allowable gross thermal loadings in radioactive waste repositories in zeolite-bearing volcanic rocks. 3 figures.
- Research Organization:
- Los Alamos National Lab., NM
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 59129
- Journal Information:
- Journal of Geology, Journal Name: Journal of Geology Vol. 90; ISSN JGEOAZ
- Country of Publication:
- United States
- Language:
- English
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