Microtomography-based Inter-Granular Network for the simulation of radionuclide diffusion and sorption in a granitic rock.
Field investigation studies, conducted in the context of safety analyses of deep geological repositories for nuclear waste, have pointed out that in fractured crystalline rocks sorbing radionuclides can diffuse surprisingly long distances deep into the intact rock matrix; i.e. much longer distances than those predicted by reactive transport models based on a homogeneous description of the properties of the rock matrix. Here, we focus on cesium diffusion and use detailed micro characterisation data, based on micro computed tomography, along with a grain-scale Inter-Granular Network model, to offer a plausible explanation for the anomalously long cesium penetration profiles observed in these in-situ experiments. The sparse distribution of chemically reactive grains (i.e. grains belonging to sorbing mineral phases) is shown to have a strong control on the diffusive patterns of sorbing radionuclides. The computed penetration profiles of cesium agree well with an analytical model based on two parallel diffusive pathways. This agreement, along with visual inspection of the spatial distribution of cesium concentration, indicates that for sorbing radionuclides the medium indeed behaves as a composite system, with most of the mass being retained close to the injection boundary and a non-negligible part diffusing faster along preferential diffusive pathways.
['Iraola|Aitor|A|', 'Trinchero|Paolo|P|', 'Voutilainen|Mikko|M|', 'Gylling|Björn|B|', 'Selroos|Jan-Olof|JO|', 'Molinero|Jorge|J|', 'Svensson|Urban|U|', 'Bosbach|Dirk|D|', 'Deissmann|Guido|G|']
D002588:Cesium Radioisotopes D003198:Computer Simulation D004058:Diffusion D005844:Geology D008962:Models, Theoretical D016062:Porosity D011850:Radioactive Waste D011868:Radioisotopes D012822:Silicon Dioxide D014875:Water Pollutants, Radioactive D055114:X-Ray Microtomography
Anomalously long cesium penetration Diffusion experiment Grain-scale model Heterogeneity of sorption sites