Conceptual Structure of Performance Assessments Conducted for the Waste Isolation Pilot Plant
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CONCEPTUAL STRUCTURE OF PERFORMANCE ASSESSMENTS CONDUCTED FOR THE WASTE ISOLATION PILOT PLANT J. C. HELTON*, M. G. MARIETTA AND R. P. RECHARD** *Arizona State University, Tempe, AZ, 85287 **Sandia National Laboratories, Albuquerque, NM87185 ABSTRACT The Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico is being developed by the U.S. Department of Energy as a disposal facility for transuranic waste. In support of this project, Sandia National Laboratories is conducting an ongoing performance assessment (PA) for the WIPP. The ordered triple representation for risk proposed by Kaplan and Garrick is used to provide a clear conceptual structure for this PA. This presentation describes how the preceding representation provides a basis in the WIPP PA for (1) the definition of scenarios and the calculation of scenario probabilities and consequences, (2) the separation of subjective and stochastic uncertainties, (3) the construction of the complementary cumulative distribution functions required in comparisons with the U.S. Environmental Protection Agency's standard for the geologic disposal of radioactive waste (i.e., 40 CFR Part 191, Subpart B), and (4) the performance of uncertainty and sensitivity studies. Results obtained in a preliminary PA for the WIPP completed in December of 1991 are used for illustration. INTRODUCTION The Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico is being developed by the U.S. Department of Energy as a disposal facility for In support of this project, Sandia National Laboratransuranic waste.[1-3] tories is conducting an ongoing performance assessment (PA) for the WIPP.[4,5] At present, a PA is carried out each year to summarize what is known about the WIPP and to provide guidance for future work. [6-8] It is anticipated that these iterative PAs will continue until the WIPP is either licensed for the disposal of transuranic waste or found to be unsuitable for such disposal. The WIPP is a complex facility, with the result that carrying out a PA is a large undertaking. Successful organization and execution of this undertaking requires a clear conceptual structure for the PA. This presentation provides an overview of the conceptual structure currently used in PAs for the WIPP and illustrates this structure with results from a PA completed in approximately December of 1991.[8-11] CONCEPTUAL BASIS FOR STRUCTURE OF WIPP PERFORMANCE ASSESSMENT As proposed by Kaplan and Garrick,[12] the outcome of a PA can be represented by a set R of ordered triples of the form
R -{(Si, psi, cSi), i-1 ... , nS},
(1)
where Si is a set of similar occurrences, pSi is the probability that an occurrence in the set Si will take place, cSi is a vector of consequences associated with Si, nS is the number of sets selected for consideration, and the sets Si have no occurrences in common (i.e., the Si are disjoint sets).
Mat. Res. Soc. Symp. Proc. Vol. 294. ý11993 Materials Research Society
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This representation formally decomposes the outcome of a PA into what can happen
(the
Si),
how
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