Non-Conservative Assumptions in the 1992 Performance Assessment for the Waste Isolation Pilot Plant
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Non-Conservative Assumptions in the 1992 PerformanceAssessment for the Waste Isolation Pilot Plant R. H. Neill and W. W.-L. Lee Environmental Evaluation Group, 7007 Wyoming NE, # F-2, Albuquerque, NM 87109 USA
ABSTRACT Performance/safety assessments have been conducted for the Waste Isolation Pilot Plant, a repository for transuranic waste in salt. We challenge two key assumptions in the 1992 Performance Assessment that led to non-conservative results. The predicted release rate of radionuclides appears underestimated due to the use of expert elicited solubilities. The overall release has been underestimated due to the use of improperly elicited human intrusion probabilities.
INTRODUCTION The Waste Isolation Pilot Plant (WIPP) is a federal repository intended for disposal of defense-generated transuranic (TRU) waste, including hazardous waste components such as heavy metals and volatile organics. The U. S. Congress assigned the Environmental Protection Agency (USEPA) the responsibility of establishing standards for the safe disposal of high-level and transuranic waste, and the task of certifying that the proposed repository complies with the standards. To demonstrate that such disposal will be safe, Sandia National Laboratories has prepared a series of performance assessments for the Department 1 of Energy (USDOE) to predict long-term system safety under a range of conditions. The Environmental Evaluation Group (EEG) performs independent technical analyses of WIPP to protect the health and environment of the people of New Mexico. This paper examines and challenges several key assumptions in the latest performance assessment.
WIPP & TRU Transuranic waste consists primarily of material (rags, tools, equipment and sludges) with a-radioactivity greater than 3.7 x 106 Bq/kg (100 nCi/g). Prior to 1970, most transuranic waste was buried at shallow depths at the generator sites. From 1970 through 1992, about 106,000 m 3 of transuranic waste were placed in retrievable storage, with a total activity of about 6.84 x 1016 Bq. 2 It is this retrievably stored transuranic waste that is destined for disposal at the WIPP. The WIPP is located in southeastern New Mexico, 40 km east of Carlsbad. The repository is in bedded salt of the Permian age, some 650 m below ground surface, in salt 600 m thick. Work on WIPP began in 1974 and several miles of drifts and tunnels have been 3 constructed. The Department of Energy plans to ultimately dispose 178,000 m of contact3 handled transuranic waste with 3.3 x 1017 Bq, along with 7100 m of remote-handled waste with 1.85 x 1017 Bq.
WIPP PERFORMANCE ASSESSMENT Before waste can be placed at the WIPP, the USEPA must certify that the WIPP will comply with USEPA's environmental standards for the disposal of high-level and transuranic
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wastes. 3 The USEPA's standards specify that for all nuclides, their cumulative releases to the accessible environment for 10,000 years after disposal from all significant processes and even
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