Status of integrated performance assessment of the waste packages and engineered barrier system

Performance assessment of the engineered barrier system for a nuclear waste repository combines information from relevant disciplines and predicts the net long-term performance of the EBS in unites of regulatory goals for performance. The performance assessment models are specific to the proposed Yucca Mountain, Nevada site. Early assessments are used for project planning and feedback. The EBS scenarios activity develops the scenarios and the consequent event sequences. Initial model development for single waste packages indicates that the radionuclide release rate performance is sensitive to the water flux, element solubilities, and/or the mode of water contact with the waste. The latter in turn depends on local scale hydrology and the modes of corrosion for the container material. For the release rate summed over waste packages, variations among waste packages and their near-field environments are anticipated. These variations place demands on data acquisition and modeling, as well as modulate the impact of localized changes of conditions. Sampling in uncertainty assessment is a subsequent step in examining the reliability of predictions made in the performance assessments. Advances made in sampling methods are referenced. 14 refs., 6 figs