United States Nuclear Regulatory Commission - Protecting People and the Environment

Hydrologic Uncertainty Assessment for Decommissioning Sites: Hypothetical Test Case Applications (NUREG/CR-6695, PNNL-13375)

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Publication Information

Manuscript Completed: January 2001
Date Published:
February 2001

Prepared by:
P.D. Meyer and R.Y. Taira
Pacific Northwest National Laboratory
P.O. Box 999
Richland, Washington 99352

T.J. Nicholson, NRC Project Manager

Prepared for:
Division of Risk Analysis and Applications
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code W6933

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Introduction

This report uses hypothetical decommissioning test cases to illustrate an uncertainty assessment methodology for dose assessments conducted as part of decommissioning analyses for NRC-licensed facilities. This methodology was presented previously in NUREG/CR-6656. The hypothetical test case source term and scenarios are based on an actual decommissioning case and the physical setting is based on the site of a field experiment carried out for the NRC in Arizona. The emphasis in the test case was on parameter uncertainty. The analysis is limited to the hydrologic aspects of the exposure pathway involving infiltration of water at the ground surface, leaching of contaminants, and transport of contaminants through the groundwater to a point of exposure. The methodology uses generic parameter distributions based on national or regional databases for estimating parameter uncertainty. A Bayesian updating method is used in one of the test case applications to combine site-specific information with the generic parameter distributions. Sensitivity analyses and probabilistic simulations are used to describe the impact of parameter uncertainty on predicted dose. Emphasis is placed on understanding the conceptual and computational behavior of the dose assessment codes as they are applied to the test cases. The primary code used in these applications was RESRAD v. 6.0, although DandD v. 1.0 results are also reported. The methods presented and the issues discussed are applicable to other codes as well.

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