Transport of radioactive substances in the non-saturated underground zone as demonstrated by means of physico-chemical pilot experiments and mathematical transport models

The aim of this R and D project was to include the non-saturated underground zone into the investigation of flow and transport processes by means of mathematic-numerical modelling. Only by taking into account seepage and transport processes in the non-saturated zone is it possible in the event of accidents to make forecasts of propagation behaviour and to effectively plan relief and decontamination measures. Corresponding models, which can simulate these processes either one or two-dimensionally (in vertical and horizontal direction) were acquired and in part developed further. The work has not yet been finalized, for one thing because of the inherent complexity of the subject and for another because the modelling of natural processes in the non-saturated zone is still the object of research. This holds true especially of the two-dimensional calculation of transport processes, which makes high demands on the calculation algorithms employed as to speed of calculation and convergence of the solution. The laboratory work carried out with a view to the determination of the sorption term also revealed the enormous amount of time required in many cases for experiments in the non-saturated zone.(orig.)