Uncertainty and Sensitivity Analysis for Gas and Brine Migration at the Waste Isolation Pilot Plant: Fully Consolidated Shaft

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Abstract
Uncertainty and sensitivity analysis techniques based on Latin hypercube sampling, partial correlation analysis, stepwise regression analysis, and examination of scatterplots are used in conjunction with the BRAGFLO model to examine two-phase flow (i.e., gas and brine) at the Waste Isolation Pilot Plant, which is being developed by the U.S. Department of Energy as a disposal facility for trans-uranic waste, to provide insights on factors that are potentially important in showing compliance with applicable regulations of the U.S. Environmental Protection Agency. Specific regulations include “Petitions to Allow Land Disposal of a Waste Prohibited Under Subpart C of Part 268” (40 CFR 268.6), which implements the Resource Conservation and Recovery Act and establishes maximum environmental concentrations for regulated chemicals such as volatile organic compounds (VOCs) and heavy metals, and “Environmental Standards for the Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive Wastes” (40 CFR 191, Subpart B), which places a probabilistic limit on allowable radioactive releases from a disposal facility over a 10 000-yr time period. The primary topics investigated are (a) gas production due to corrosion of steel, (b) gas production due to microbial degradation of cellulosics, and (c) gas migration into anhydrite marker beds in the Salado Formation, which is the host unit into which the waste will be emplaced. Gas production and movement is of particular importance in establishing compliance with 40 CFR 268.6 because of its influence on the movement of VOCs. Important variables identified in the analysis include (a) initial brine saturation of the waste, (b) stoichiometric terms for corrosion of steel and microbial degradation of cellulosics, and (c) gas barrier pressure in the anhydrite marker beds.