An approach to the assessment of high-level radioactive waste containment. I: Waste package degradation

A description is presented of the various models (i.e. thermal, chemical environment, humid-air and aqueous corrosion) used in the engineered barrier system performance assessment code (EBSPAC) to represent processes that govern the failure of waste packages (WPs) and, ultimately, the release of radionuclides from the engineered barrier system (EBS). These models are specifically adapted to the US Department of Energy (DOE) WP design, adopted in 1996, for the proposed repository at Yucca Mountain (YM), NV. The design consists of a double-wall overpack composed of two concentric containers of different metallic materials in a horizontal drift emplacement. EBSPAC was developed to deterministically evaluate the performance of the engineered barriers and to be used as the source term module incorporated in the Center for Nuclear Waste Regulatory Analyses (CNWRA)/Nuclear Regulatory Commission (NRC) total performance assessment (TPA) code. EBSPAC essentially consists of two separate codes. The code dealing with WP failure calculations is the focus of this paper and the other, dealing with radionuclide release, is described in a companion paper. An example problem is presented to illustrate the results obtained with the code analyzing the influence of several critical input parameters, related to the repository and EBS designs and the resulting environmental conditions, on WP failure.

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