2013

Kajanto, Karita

a) Background b) What should be done? c) Methods and tool a) Estimating the long term safety of a geological nuclear waste repository is a complicated computational problem. Numerous scenarios of system failure must be taken into account. Released radionuclides can be transported long distances along the groundwater of rock fractures. Sorption into the bedrock may also take place. In the case of a release of radionuclides to the groundwater, transport properties in fractures must be well known. A common approximation of rock fracture flow is flow between parallel plates. The shape of natural fractures, however, is uneven and irregular. Varying shape and size causes dispersion that affects transport. b) Study the effect of dispersion caused by variable aperture fractures to the transport and flow properties. Build models of a single rock fracture in different credible geometries. Calculate the flow field and transport of a pulse of radionuclides trough the fractures. Also, calculate the retention of nuclides caused by matrix diffusion. Compare the results to the parallelplate case. c) Numerical methods: FEM with time integration. COMSOL Multiphysics 4.2a, CAD Import Module, Subsurface Flow Module, Chemical Reaction Engineering Module.