Summary discussion of the 1996 performance assessment for the Waste Isolation Pilot Plant

The Waste Isolation Pilot Plant (WIPP) is under development by the US Depar tment of Energy (DOE) for the geologic disposal of transuranic waste. The c onstruction of complementary cumulative distribution functions (CCDFs) for total radionuclide release from the WIPP to the accessible environment is d escribed. The resultant CCDFs (i) combine releases due to cuttings and cavi ngs, spallings, direct brine release, and long-term transport in Rowing gro undwater; (ii) fall substantially to the left of the boundary line specifie d by the US Environmental Protection Agency's (EPA's) standard 40 CFR 191 f or the geologic disposal of radioactive waste; and (iii) constitute an impo rtant component of the DOE's successful Compliance Certification Applicatio n to the EPA for the WIPP. Insights and perspectives gained in the performa nce assessment (PA) that led to these CCDFs are described, including the im portance of: (i) an iterative approach to PA; (ii) uncertainty and sensitiv ity analysis; (iii) a clear conceptual model for the analysis; (iv) the sep aration of stochastic (i.e. aleatory) and subjective (i.e, epistemic) uncer tainty; (v) quality assurance procedures: (vi) early involvement of peer re viewers, regulators, and stakeholders; (vii) avoidance of conservative assu mptions; and (viii) adequate documentation. Published by Elsevier Science L td.