Sedimentary Geology and its Potential Role in Storing Nuclear Waste

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

• Long-term disposal of high-level radioactive
  waste
• Wastes dangerous 10 000 years
• Need safe, stable storage of materials for
  unprecedented time periods

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Requirements for Safe Repositories

• Remote area far from major population centers
• Arid area
• Above water table
• Far from major water/well sources
• Long residence time of water

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Requirements (Continued)

• High geological stability
• Low earthquake activity
• Low volcanic activity
• Few fractures
• Predictable long-term homeostasis of environment

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Why Sedimentary Rocks?

• Suitable host rocks Clays, mudstones, shales
• Fine grained
• Low porosity
• Laterally extensive
• Homogeneous

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Why Sedimentary Rocks?

• Clay rich sediments are best
• Low hydraulic conductivity
• Long residence time
• Uncemented deposits retain plasticity
• Self-sealing discontinuities

Not this clay...
More like this
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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)

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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

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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)

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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.

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

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(No Transcript)
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Why Yucca?

• 350m underground
• Arid desert climate (gt20cm annual precip.)
• Water mobility very low in host rocks
• Surrounding area already contaminated (Weapons
  tests)

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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...
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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

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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.

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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

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Shh I didnt say nuthin