Yucca Mountain and the Geologic Disposal of HighLevel Nuclear Waste

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Yucca Mountain and the Geologic Disposal of
High-Level Nuclear Waste

• Allison Macfarlane
• March 28, 2008
• Deane Conference
• Lake Forest College

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High-Level Nuclear Waste Options

• Geologic disposal best option
• Others include
• outer space (too risky)
• deep sea sediments (too much water circulation
  international waters)
• leave it where it is (interim storage sufficient
  for 100-years, not longer)
• Geologic storage will be needed for any fuel
  cycle, open or closed
• Site selection most important aspect of geologic
  disposal

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Siting a Geologic Repository

• Use multi-barrier system
• Natural and Engineered
• Siting Criteria
• Long-term tectonic stability
• Low-groundwater content and flow
• Stable geochemistry at depth, including a
  reducing environment and equilibrium between rock
  and water
• Excavatable
• Also need
• Deep enough, large perimeter/far from populations
  - but accessible to transport
• No potential for human intrusion

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Is Yucca Mountain a Reasonable Site?

• Depends on time frame
• For 1,000 years, yes
• For 10,000 years, maybe not
• Violates 2 of 4 IAEA siting criteria
• Tectonically active
• Oxidizing (not reducing) geochemical environment
  within the repository
• This requires more engineered fixes and there
  is greater uncertainty as to how the repository
  will perform over time compared to sites in other
  countries

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Volcanism

• 5 volcanoes within 20 km of Yucca Mtn
• All younger than 2 million years
• Youngest is Lathrop Wells 80,000 years
• Could a new volcanic center form under YM? 2
  possibilities
• Explosive eruption
• Magma doesnt vent but fills drifts - corrosive
  gases, thermal effects
• Current probability estimates
• DOE 5.4 x 10-9 to 4.9 x 10-8 events/yr
• NRC 10-7 to 10-8 events/yr
• Remaining Uncertainties
• buried basalts (from magnetic anomaly data)
  suggest the number of young events in the area
  could be larger than initially thought

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Oxidizing Environment Effect on Spent Fuel

• Spent Fuel - Uranium dioxide (UO2) - not stable
  under oxidizing conditions in presence of water
• Forms complexes with common species
• Complexes are highly soluble in water
• These reactions will occur within 100-1,000 years
• US only country using an oxidizing environment
  for high-level waste storage
• introduces large uncertainties for the waste and
  the canister that holds the waste
• Uncertainties multiple
• E.g., how alteration products will behave over
  time and how quickly they will release
  radionuclides

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Will Yucca Mt Be Enough?

• Statutory limit 70,000 MT
• 63,000 MT for spent fuel
• DOE EIS limit 119,000 MT
• Total spent fuel defense waste 140,000 MT
• Assumes no new reactors built
• Assumes all reactors given license extensions
• DOE required by NWPA to determine need for second
  repository between 2007-2010

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Constraints on Yucca Repository Capacity

• Waste Itself
• Volume
• Heat (age, burn-up)
• Radioactivity
• Geology of the Site
• Distribution of faults/fractures
• 2 effects mining ease and fast water pathways
• Volcanism
• Water table
• Increases in elevation to N/NW
• Lithological variation
• Repository unit thins to N/NE and WNW (must be
  gt200m)
• Presence of Lithophysae (need lt15-20
  lithophysae)
• Land ownership/Mineral rights

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Conclusions

• Best solution for high-level nuclear waste
  geologic repositories
• Yucca Mt may not be suitable for the long-term
• Tectonically active, oxidizing environment
• Most likely, well need more than Yucca Mtn
• Yucca Mts capacity will be limited by geology,
  and there might be a nuclear renaissance
• We need a Plan B for high-level waste in the US
  
• Interim storage
• Alternative sites for repositories