| Abstract: |
The use of cementitious materials has been proposed in a variety of waste management systems because these materials can have a variety of desirable performance characteristics: hydraulic isolation, chemical isolation, structural stability. Cementitious barriers are commonly engineered with a goal of achieving the highest quality material possible (e.g. minimizing hydraulic conductivity, porosity, tortuosity, diffusivity). However, a single performance goal may not be optimum when practical considerations of designs and performance characteristics are considered simultaneously. In addition, laboratory-scale optimized designs may have field-scale characteristics that are less than ideal. Abstracted performance assessment calculations are used to develop risk insights for the performance of cementitious materials in waste disposal or remediation applications. The generic applications considered are the use of cements as a waste matrix (i.e., the radioactivity is incorporated into the hydrating cement matrix) and the use of cements as a resistive barrier (i.e., the radioactivity comes into contact with a hydrated cement matrix) to reduce water contact and decrease mobilization from residual radioactivity remaining in a closed waste storage tank or other system undergoing remediation. Uncertainty analysis using genetic algorithms is used to identify key variables and uncertainties. In addition, stylized calculations are performed to demonstrate the importance of conceptual model uncertainty. Designs with real features are evaluated and compared to idealized representations. |
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