Natural and Engineered Barriers at the Waste Isolation Pilot Plant

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Natural and Engineered Barriers at the Waste
Isolation Pilot Plant

• Frank D. Hansen
• Sandia National Laboratories
• SAND2008-6989P

Sandia is a multiprogram laboratory operated by
Sandia Corporation, a Lockheed Martin
Company,for the United States Department of
Energys National Nuclear Security
Administration under contract DE-AC04-94AL85000.
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WIPP A Solution of a National Problem
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Waste Types/Packaging
Various Transuranic Waste Packages
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TRUPACT-II Shipping Container

• Built and maintained according to Nuclear
  Regulatory Commission standards
• Tested to ensure containment of radioactive
  materials

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Waste Types/Packaging

• Monitored by satellite tracking system
• Drivers are highly trained
• Procedures for accident prevention
• Emergency responders are trained

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Unloading Typical Waste Packages
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CH Waste in Disposal Room
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Bedded Salt Was Chosen for the Siting of the US
Defense Nuclear Wastes

• Salt can be mined easily
• Salt has a relatively high thermal conductivity
• Wide geographic distribution (many potential
  sites)
• Salt is plastic
• Salt is essentially impermeable
• Fractures in salt are self healing
• Salt has existed underground for millions of
  years
• Attributes of Natural Barrier

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Natural Barrier of the Delaware Basin
1981 First shaft completed 1996 CCA submitted
to EPA 1998 WIPP certified by EPA 1999 First
waste shipment received 2004 First
recertification 2007 Begin RH disposal
WEST
EAST
Castile Formation
Location of WIPP
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WIPP Underground Layout
Shaft Seal System
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Full Scale Behavior
Figure 2. Typical Level of Agreement between
Underground Test Results and Predicted Closure
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Salt Behavior is well Understood
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WIPP Disposal Room Evolution
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Disturbed Rock Zone around a Disposal Room
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WIPP Room Evolution at Time0 years
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WIPP Room Evolution at Time12 years
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WIPP Room Evolution at 1000 years
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Shaft Seal System Design Guidance

• Limit hazardous constituents reaching regulatory
  boundaries
• Restrict groundwater flow through the sealing
  system
• Use materials possessing mechanical and chemical
  compatibility
• Protect against structural failure of system
  components
• Limit subsidence and prevent accidental entry
• Utilize available construction methods and
  materials

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Material Specification

• Functions
• Material characteristics
• Construction
• Performance requirements
• Verification methods

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Shaft Sealing System
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Shaft Seal System Conclusions

• The WIPP shaft seal system effectively limits
  fluid flow within the seal system.
• Brine flow volumes from the Rustler downward are
  insignificant relative to the salt-column gas
  saturated pore volume and the repository pore
  volume.
• The salt column becomes an effective barrier to
  gas and brine migration by 100 years after
  closure.
• Long-term flow rates within the seal system are
  limited.

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Option D Panel Closure System
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Proposed Panel Closure System
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Definition of Barriers

• EPA defines barriers as any material or
  structure that prevents or substantially delays
  movement of water or radionuclides toward the
  accessible environment
• Barriers can be a geologic structure, a
  canister, a waste form, or a material placed over
  and around waste provided that material or
  structure substantially delays movement of water
  or radionuclides

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MgO Engineered Barrier

• MgO will act as an engineered barrier in the WIPP
  by decreasing actinide solubilities.
• Will remove CO2 and control PCO2 and pH within
  favorable ranges.
• Only engineered barrier recognized by EPA.
• Ongoing lab studies imply MgO will effectively
  remove H2O and CO2.

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Natural and Engineered Barriers Summary

• Site Selection/Characterization Studies
• Geologic mapping of surface and borehole data.
• Geophysical surveys for structure, brine pockets.
• Geochemistry/Mineralogy for geologic process
  analysis.
• Hydrology Program
• Characterize the flow and transport in subsurface
  ground water through field and lab tests and
  describe with flow models.
• Chemistry Program
• Estimate the solubility and mobility of
  radionuclides in WIPP environment through
  experiments.
• Sorption of actinides during transport.

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Natural and Engineered Barriers Summary

• Rock Mechanics and Shaft Seal Design
• Measure and predict behavior of salt around waste
  rooms
• Design an effective, impermeable shaft seal
  system using natural and man-made materials
• Performance Assessment Modeling
• Comparison to the EPA standards
• Compliance Certification Application

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Natural and Engineered Barriers Summary

• Robust Site Confirmed through Selection and
• Characterization Studies
• Natural Barriers include Salt Formation
• Room Enclosure, Fractured healing, and
  Entombment
• Favorable Hydrological Setting
• Minimal Water
• Flow Characterized and Modeled
• Engineered Barriers
• Shaft Seals and Panel Closure Systems
• MgO Assurance