INTRAVAL phase 2, test case Mol. Simulation of the underground migration experiment

Abstract

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Mathematical models are frequently used in risk analysis for underground disposal of nuclear waste. The validity of these models is examined in an international validation project INTRAVAL. RIVM participates in INTRAVAL project for the validation of the code METROPOL, a groundwater flow and solute transport program developed at RIVM. Within INTRAVAL several test-cases have been formulated. One of these test cases is an in-situ migration experiment in an argillaceous formation at 220 meters depth at Mol, Belgium. This experiment has been set up to examine whether parameters derived from laboratory experiments may be used for long term predictions on a larger scale. The present report describes the simulations of the experiment with the METROPOL code and it discusses an analytical solution of the problem. The simulation results indicate that the model concept of the METROPOL code provides an adequate description of the tracer migration in the Boom clay at the Mol site. However, to prevent discretization errors, a fine mesh is required to model the process in areas where steep concentration gradients are expected. Application of fine meshes leads to a larger number of nodal points and, consequently, to an increase of required computer memory and CPU time consumption. With respect to the parameters from the laboratory tests, it is shown these can be used for long term predictions of problems at field scale.