Calibration and Reliability in Groundwater Modelling: Credibility of Modelling

(Proceedings of ModelCARE 2007 Conference, held in Denmark, September 2007). IAHS Publ. 320, 2008, 278-283.

The influence of the experimental set-up and the model approach on the determination of diffusion coefficients for radionuclides in laboratory column experiments

Wilfried Pfingsten

Waste Management Laboratory, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

wilfried.pfingsten@psi.ch

Abstract One- and two-dimensional modelling is used to estimate the differences between diffusion coefficients deduced from laboratory diffusion experiments for tracers with different sorption characteristics. Depending on sample thickness, filter thickness, heterogeneous tracer injection and extraction, and heterogeneous sorption processes on the sample and filter material, differences are calculated for differently sorbing radionuclides. It is shown that for non-sorbing radionuclides, thin filters and samples, 1- and 2-D analysis of diffusion experiments yield similar results. For weakly/strongly sorbing radionuclides, where thinner samples are generally used in the experiments to reduce the experimental time, and where reactions with filters increase, the precise determination of the diffusion coefficients becomes more difficult.

Key words diffusion coefficient; model set-up; heterogeneous sorption; data interpretation; 1-D modelling; 2-D modelling