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Total System Performance Assessment: Enhanced Design Alternative IV

Description: The purpose of this calculation is to document total system performance assessment modeling of Enhanced Design Alternative (EDA) Feature IV. Total System Performance Assessment (TSPA) calculations for EDA IV are based on the TSPA-VA Base Case which has been modified with a quartz sand invert, quartz sand backfill, line loading and 21 PWR waste packages that have 2-cm thick titanium grade 7 corrosion resistant material (CRM) drip shields that are placed over a 30 cm thick carbon steel (A5 16) waste package with an integral filler material (CRWMS M&O 1999a & 1999b). This document details the changes and assumptions made to the VA reference Performance Assessment Model (CRWMS M&O 1998a) to incorporate the design changes detailed for EDA IV. The performance measure for this evaluation is the expected value dose-rate history at 20 km from the repository boundary.
Date: June 23, 1999
Creator: Mattie, P.D.
Partner: UNT Libraries Government Documents Department

Methods and Techniques Used to Convey Total System Performance Assessment Analyses and Results for Site Recommendation at Yucca Mountain, Nevada, USA

Description: Total System Performance Assessment (TSPA) is used as a key decision-making tool for the potential geologic repository for high level radioactive waste at Yucca Mountain, Nevada, USA. Because of the complexity and uncertainty involved in a post-closure performance assessment, an important goal is to produce a transparent document describing the assumptions, the intermediate steps, the results, and the conclusions of the analyses. An important objective for a TSPA analysis is to illustrate confidence in performance projections of the potential repository given a complex system of interconnected process models, data, and abstractions. The methods and techniques used for the recent TSPA analyses demonstrate an effective process to portray complex models and results with transparency and credibility.
Date: April 13, 2001
Creator: Mattie, P. D.; McNeish, J. A.; Sevougian, D. S. & Andrews, R. W.
Partner: UNT Libraries Government Documents Department

Methodology Used for Total System Performance Assessment of the Potential Nuclear Waste Repository at Yucca Mountain (USA)

Description: The U.S. Department of Energy and its contractors are currently evaluating a site in Nevada (Yucca Mountain) for disposal of high-level radioactive waste from U.S. commercial nuclear plants and U.S. government-owned facilities. The suitability of the potential geologic repository is assessed, based on its performance in isolating the nuclear waste from the environment. Experimental data and models representing the natural and engineered barriers are combined into a Total System Performance Assessment (TSPA) model [1]. Process models included in the TSPA model are unsaturated zone flow and transport, thermal hydrology, in-drift geochemistry, waste package degradation, waste form degradation, engineered barrier system transport, saturated zone flow and transport, and biosphere transport. Because of the uncertainty in the current data and in the future evolution of the total system, simulations follow a probabilistic approach. Multiple realization simulations using Monte Carlo analysis are conducted over time periods of up to one million years, which estimates a range of possible behaviors of the repository. The environmental impact is measured primarily by the annual dose received by an average member of a critical population group residing 20 km down-gradient of the potential repository. In addition to the nominal scenario, other exposure scenarios include the possibility of disruptive events such as volcanic eruption or intrusion, or accidental human intrusion. Sensitivity to key uncertain processes is analyzed. The influence of stochastic variables on the TSPA model output is assessed by ''uncertainty importance analysis'', e.g., regression analysis and classification tree analysis. Further investigation of the impact of parameters and assumptions is conducted through ''one-off analysis'', which consists in fixing a parameter at a particular value, using an alternative conceptual model, or in making a different assumption. Finally, robustness analysis evaluates the performance of the repository when various natural or engineered barriers are assumed to be degraded. The objective of ...
Date: March 15, 2001
Creator: Devibec, E.; Sevougian, S.D.; Mattie, P.D.; McNeish, J.A. & Mishra, S.
Partner: UNT Libraries Government Documents Department