Lessons Learned from Characterization, Performance Assessment, and EPA Regulatory211 Review of the 1996 Actinide Source Term for the Waste Isolation Pilot Plant

摘要

The Waste Isolation Pilot Plant (WIPP) is a US Department of Energy (DOE)211u001efacility for the permanent disposal of transuranic waste from defense activities. 211u001eIn 1996, the DOE submitted the Title 40 CFR Part 191 Compliance Certification 211u001eApplication for the Waste Isolation Pilot Plant (CCA) to the US Environmental 211u001eProtection Agency (EPA). The CCA included a probabilistic performance assessment 211u001e(PA) conducted by Sandia National Laboratories to establish compliance with the 211u001equantitative release limits defined in 40 CFR 191.13. An experimental program to 211u001ecollect data relevant to the actinide source term began around 1989, which 211u001eeventually supported the 1996 CCA PA actinide source term model. The actinide 211u001esource term provided an estimate of mobile dissolved and colloidal Pu, Am, U, Th, 211u001eand Np concentrations in their stable oxidation states, and accounted for effects 211u001eof uncertainty in the chemistry of brines in waste disposal areas. The 211u001eexperimental program and the actinide source term included in the CCA PA 211u001eunderwent EPA review lasting more than 1 year. Experiments were initially 211u001econducted to develop data relevant to the wide range of potential future 211u001econditions in waste disposal areas. Interim, preliminary performance assessments 211u001eand actinide source term models provided insight allowing refinement of 211u001eexperiments and models. Expert peer review provided additional feedback and 211u001econfidence in the evolving experimental program. By 1995, the chemical database 211u001eand PA predictions of WIPP performance were considered reliable enough to support 211u001ethe decision to add an MgO backfill to waste rooms to control chemical conditions 211u001eand reduce uncertainty in actinide concentrations, especially for Pu and Am. 211u001eImportant lessons learned through the characterization, PA modeling, and 211u001eregulatory review of the actinide source term are (1) experimental 211u001echaracterization and PA should evolve together, with neither activity completely 211u001edominating the other, (2) the understanding of physical processes required to 211u001edevelop conceptual models is greater than can be represented in PA models, (3) 211u001eexperimentalists should be directly involved in model and parameter abstraction 211u001eand simplification for PA, and (4) external expert review should be incorporated 211u001eearly in a project to increase confidence long before regulatory reviews begin.