Appraisal of nuclear waste isolation in the vadose zone in arid and semiarid regions (with emphasis on the Nevada Test Site)

Abstract

An appraisal was made of the concept of isolating high-level radioactive waste in the vadose zone of alluvial-filled valleys and tuffaceous rocks of the Basin and Range geomorphic province. Principal attributes of these terranes are: (1) low population density, (2) low moisture influx, (3) a deep water table, (4) the presence of sorptive rocks, and (5) relative ease of construction. Concerns about heat effects of waste on unsaturated rocks of relatively low thermal conductivity are considered. Calculations shov; that a "standard" 2000-acre repository with a thermal loading of 40 kw/acre in partially saturated alluvium or tuff would experience an average temperature rise of less than 100°C above the initial temperature. The actual maximum temperature would depend strongly on the emplacement geometry. Concerns about seismicity, volcanism, and future climatic change are also mitigated. The conclusion reached in this appraisal is that unsaturated zones in alluvium and tuff of arid regions should be investigated as comprehensively as other geologic settings considered to be potential repository sites. DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom mendation, or favoring by the United States Government or any agency thereof. Figure A12. Thermal conductivities of quartz-rich, consolidated sand stones * 115 Figure A13. Ratio of the effective thermal conductivity of unsaturated rock to that of the saturated rock deduced from different weighting models 117 Figure A14. increase in repository temperature in a dry rock medium based on geometric mean model 118 xi LIST OF TABLES Table 1. Thermal conductivities of alluvium 23 Table 2. Thermal and mechanical properties of alluvium 24 Table 3. Principal advantages and concerns of waste isolation in the unsaturated zone of Basin and Range alluvial-filled valleys * 47 Table 4. Ranges of sorption ratios in tuff from Yucca Mountain and Jackass Flats • 55TeJale 5. Thermal and mechanical properties of tuff 57 Table 6. General stratigraphy of Yucca Mountain in the vicinity of drill hole UE25a-1 69 Table 7. Comparison of advantages and concerns of locating a repository in various tuff units 82 Table 8. Hydraulic properties of tuffaceous units ..... 87 Table 9. Assets, concerns, and unknowns of siting a repository in tuffaceous rock above the water table at Yucca Mountain 88 Table 10. Major advantages and concerns of waste isolation in unsaturated and saturated regimes 93 Tabl...

Fixed-fugacity option for the EQ6 geochemical reaction path code

“…This document describes a capability that has been added to the EQ6 code that permits the eval uation of chemical reactions occurring in the un saturated zone. Since oxidizing conditions are ex pected in the unsaturated zone at Yucca Mountain (Roseboom, 1983;Wollenberg et al, 1983), the ex change of 0 2 and C0 2 should be especially sig nificant. The unsaturated zone can be conceptual ized as a large external reservoir containing 0 2 and CC* 2 at fixed fugacities.…”