This document summarizes a presentation given by Kathleen Economy from the EPA on the EPA's regulatory perspective on the Waste Isolation Pilot Plant (WIPP) radioactive waste repository. It discusses how the EPA initially certified WIPP in 1998 and requires recertification every 5 years. It notes how understanding of salt behavior and waste characteristics has increased significantly since then. The EPA is focusing its review on ensuring models accurately capture near-term salt behavior based on new data, which increases confidence in long-term performance predictions. Challenges include determining what new information needs to be incorporated into performance assessments during recertification.

1. 7th US/German Workshop on Salt Repository
Research, Design, and Operation
Kathleen Economy
U.S. Environmental Protection Agency
Washington, DC USA
Washington, DC
September 7-9, 2016

2. WIPP and the Safety Case –
A Regulator’s Perspective
Kathleen Economy
U.S. Environmental Protection Agency
Washington, DC USA
Presented at:
7th US/Germany Workshop on Salt Repository Research, Design and Operation
Crystal City, Virginia USA
September 7-9, 2016

3. EPA’s Review and Considerations Related to the WIPP Repository
 1996 – DOE submits license application to EPA, EPA evaluated the
available information
 1998 - EPA issues certification to DOE after modifications were made to
the application
 1999 – First waste emplaced at WIPP
 Once first waste emplaced a periodic 5-year recertification required
 Recertification needs to include updated information
 Two Cases Evaluated for WIPP
 Undisturbed Case - The base case, a wide compliance margin
 Disturbed Case – Drilling due to oil, gas, and mineral exploration
 Requires human intrusion from drilling be incorporated into analysis
 Multiple intrusions assumed, number dependent upon updated drilling
rates

4. Since WIPP’s 1998 Certification
 With 20+ years of operation, a larger and more sophisticated
knowledge base exists on salt and other components
 Many more ‘Mores’
 More and deeper understanding of salt behavior post excavation
 More experimental data on actinide chemistry in repository
environment
 More knowledge of waste characteristics
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5. A Component of Reviewing WIPP PAs
1990s Data
 Developed parameter distributions,
end-points, means intended to cover
uncertainties
 Post 1990s - Significantly more data,
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Conservative Probability Distribution
Developed Due to Limited Data
1980’s – 90’s
Limited Available Data
Time/Experience
Current data and Distributions
‘New Data’
Post 1990s - Significantly more data, therefore
parameter distributions have less uncertainty

6. Challenges in the EPA’s Five Year Recertification Review
 Parameters ranges and values and assumptions considered as acceptable in
the past may now not be considered as suitable due to increased knowledge
 Need to periodically reevaluate that which was suitable in past PAs is still
suitable and applicable in the required PA updates
 Evolving information presents challenges to the developer and regulator:
 What is reasonable and suitable in periodically updating repository
Performance Assessments?
 What are the “tipping points” for including new information and conducting
new analyses?
 What should the regulator (EPA) require versus accepting or depending on
what the operator (DOE) provides?
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7. EPA is Looking at Near-Term Behavior of Salt
 EPA evaluating how relevant experimental data are updated in the array
of PA input parameters to capture initial conditions
 Now, there is a higher level of confidence in ‘nailing’ what will happen
within 100 to 500 years post-closure
 First assure confidence in near-term time predictions
 From there predict onward to 10,000 years
 Increased focus on near-term behavior boosts level of confidence in
predictions of long term performance
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