Development of a methodology of geochemical sensitivity analysis for performance assessment

The objective of this geochemical sensitivity analysis is to formulate criteria for valid simplification of radionuclide transport models used in performance assessment. In the past, limitations in available models, data, and computer codes have necessitated the use of simplified representations of radionuclide chemistry and water/rock interactions in analyses of high-level waste (HLW) repositories. The validity of these simplifying approximations is a crucial element in the design of performance assessment methods and must be assessed relative to the appropriate performance measure and ranges of physicochemical parameter values. In this paper, we illustrate the complementary roles played by (1) simple transport models designed to bound the radionuclide discharge over wide ranges of physicochemical conditions, (2) detailed geochemical models that provide a structured method to obtain reliable information about solute/rock/water interactions, and (3) sensitivity and uncertainty analysis techniques used to assess the significance of errors in both data and models