A probabilistic study of the effect of retardation factor uncertainty using a compartment model for radionuclide release into the biosphere

The effect of retardation factor uncertainty with reference to the results of a compartment model, representing radionuclide release into the biosphere from a disposal facility, is studied through the application of polynomial chaos theory. We review the derivation of the working equations and apply the polynomial chaos expansion to these equations. The uncertainty in the retardation factor typically covers several orders of magnitude and stems from uncertainties in the distribution coefficient, these large uncertainties make any quantitative analysis of radionuclide release highly problematic. In this paper, we assume that the uncertainty in the retardation factor is fully described by a log-uniform distribution. We compare results using polynomial chaos against a semi-analytical solution for a short decay chain and present numerical results from polynomial chaos applied to a longer generic decay chain.