Preliminary Performance-Based Analyses Relevant to Dose-Based Performance Measures for Proposed Geologic Repository at Yucca Mountain (NUREG-1538)

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• NUREG-1538
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Publication Information

Manuscript Completed: August 1999
Date Published: October 2001

Edited by:
T. J. McCartin, M. P. Lee

Division of Waste Management
Office of Nuclear Material Safety and Safeguards
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Center for Nuclear Waste Regulatory Analyses
6220 Culebra Road
San Antonio, TX 78228-5155

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Abstract

The National Academy of Sciences' (NAS') Committee on Technical Bases for Yucca Mountain (Nevada) Standards recommended that standards for the disposal of high-level radioactive waste (HLW) at Yucca Mountain should: (1) set a limit on the risk to individuals; (2) use the critical group approach, as defined by the International Commission on Radiological Protection; (3) define the critical group using present knowledge and cautious, reasonable assumptions; (4) use a time period for conducting compliance assessment that includes the period of greatest risk; and (5) use a stylized calculation to assess whether the repository's performance would be substantially degraded as a consequence of a postulated intrusion. The staff and its technical assistance contractor-the Center for Nuclear Waste Regulatory Analyses-have undertaken a series of focused technical analyses to better understand the NAS recommendations and their implementation within the U.S. Nuclear Regulatory Commission's HLW performance assessment program. Overall, the staff believes that it will be able to integrate a dose-based approach into its regulatory framework and supporting guidance. The staff was able to: (1) tentatively identify characteristics for two potential receptor groups-"farming" and "residential" (non-farming)-using information for lifestyles and water-use practices presently occurring in the Yucca Mountain area and in other, similar, environments; (2) ascertain the potential for reducing radionuclide concentrations in ground water caused by dispersive transport processes (reduction of 1 to 75 times) and borehole mixing in a pumping water well (reduction of 1 to 50 times); (3) describe an approach to implement a dose calculation for the residential [mean dose of 30 millirem (mrem)] and farming (mean dose of 10 mrem) receptor groups; (4) describe an approach to implement a dose calculation for direct disruption of the repository from volcanic activity (probability weighted dose of about 1 mrem); (5) describe an approach to a stylized calculation for human intrusion; and (6) evaluate the time dependence of radiological hazard of HLW by comparison with naturally concentrated uranium in an ore body (after 10,000 years the relative radiological hazard of HLW has decreased by 99.9 percent and is within less than an order of magnitude of the hazard of the hypothetical ore body).