1. Sedimentary Geology and its Potential Role in Storing Nuclear Waste By J.C. Routhier and Gabrielle Pang Catering to future generations of the nuclear family...

2. ► Long-term disposal of high-level radioactive waste ► Wastes dangerous ~ 10 000 years ► Need safe, stable storage of materials for unprecedented time periods Problem:

3. ► Remote area far from major population centers ► Arid area  Above water table  Far from major water/well sources  Long residence time of water Requirements for Safe Repositories

4. ► High geological stability  Low earthquake activity  Low volcanic activity  Few fractures  Predictable long-term homeostasis of environment Requirements (Continued)

5. ► Suitable host rocks: Clays, mudstones, shales  Fine grained  Low porosity  Laterally extensive  Homogeneous Why Sedimentary Rocks?

6. ► Clay rich sediments are best  Low hydraulic conductivity  Long residence time  Uncemented deposits retain plasticity  Self-sealing discontinuities Not this clay... More like this

7. Problems with Clay ► Clays can lose plasticity ► Radionuclides may travel faster through clay than previously predicted ► Possibility of sharp grain size changes vertically and horizontally (paths of lesser resistance)

8. Evaporite Deposits ► Both bedded and salt domes are suitable ► Transport of radionuclides in salt very slow ► Plastic behavior  self- sealing ► Higher thermal diffusivity than clay

9. Problems with Evaporites ► Beds of K and Mg-rich salts dissolve more easily than rock salt ► Can lead to pathways for easier transport of radionuclides ► Salt domes produced by density instability (possibility of later recurrence)

10. Waste Disposal around the Globe ► German repositories planned in salt domes ► Belgium, France, Spain, Switzerland, Japan use Argillaceous repositories ► Canada is planning a deposit in crystalline basement rock of the Canadian shield ► U.S. planning a major repository in Yucca mountain, Nevada.

11. Why Yucca Mountain? (the “Screw Nevada Bill”) “What you are watching is an exercise in pure politics…I am participating in a nonscientific process- sticking it to Nevada” – Rep. Al Swift, Washington

12. Why Yucca? ► Located within a thick sequence of welded rhyolitic tuff ► Welded tuff  layers of hot ash accumulate and are welded together by the surrounding heat ► Very remote area (no residents)

14. Why Yucca? ► 350m underground ► Arid desert climate (>20cm annual precip.) ► Water mobility very low in host rocks ► Surrounding area already contaminated (Weapons tests)

15. Why Yucca? ► 350m above average water table ► Closed water basin (land slopes up in all directions) ► Underlying aquifer does not supply water to population centers Follow the light...

16. Problems with Yucca ► Syzmanski Theory:  Possibility of upwelling of warm water due to deep fault movement  Upwelling dates to ~10 000 years ago  Left behind calcium carbonate deposits  Warm upwelling very dangerous to repository

17. Problems with Yucca ► Sundance fault passes through proposed repository site ► 32 other nearby faults present and recently active ► Heat production of waste could turn water into steam, produce fractures and vent radioactive gas.

18. Problems with Yucca ► Seismicity concerns  Yucca relatively close to plate boundary  Recent magnitude 5.6 earthquake in 1992 ► Volcanic concerns  Lathrop Wells Volcano (18km from proposed repository) may have been active 5k-20k years ago

19. Shh… I didn’t say nuthin’