Sensitivity analyses of a geological repository for radioactive waste disposal in clay

The performance assessments of the possible geological disposal of radioactive wastes in the Boom clay layer at the Mol site have been complemented recently with sensitivity studies within the framework of the CEC's EVEREST project. For the clay layer various elements of conceptual model uncertainty are evaluated. The results obtained with a simplified one-dimensional model are compared with the results obtained from a more complicated three-dimensional model, which takes into account the anisotropy of the diffusion in the clay layer. The influence of solubility limits in the near field on the releases of radionuclides from the clay layer is demonstrated. Also the potential influence of complexation of actinides by fulvic acids is evaluated. For the aquifer system the degree of complication, that is needed to ensure a realistic modelling of the transport, is being tested. The spreading of the contamination by the radionuclides in the aquifers is simulated and the influence of the location of future water wells on the resulting doses is evaluated. Stochastic calculations are performed to assess the influence of the uncertainties in the model parameters on the calculated dose rates. The influence of the expected changes of future climate on the behavior of the repository system is taken into account as well as their impact on the uncertainties in the parameters of the geosphere models. A sensitivity analysis is carried out to rank the considered model parameters. For the case of the exploitation scenario the consequences of the use of water pumped from a water well sunk in the deep underlying aquifer are analyzed. The calculations show that the extent of the contamination in the aquifer is limited by rediffusion of radionuclides into the host clay and the deeper clay layers. Calculations show that the consequences resulting from the poor sealing scenario depend on the distance between the disposed waste and the access shaft