Technical Report NTB 85-55
Final Report of the Migration in a Single FractureExperimental results and evaluation
Three fractures in granitic rock have been investigated by hydraulic testing and by migration tests with non-sorbing as well as with sorbing tracers. The sorbing tracers were Cs, Sr, Eu, Nd, Th and U.
The fractures are located in drifts at 360 m depth in the Stripa mine in mid Sweden. The fractures are clearly visible in the drifts. There is natural water flow in the fractures. Injection took place at 5 – 10 m distance from the roof of the drifts. The water was collected at 10 – 15 locations on every fracture as it intersects the drift. Injection and collection of water was done during more than 7 months in one of the fractures. The fracture where the sorbing tracers were injected was excavated after the test and the surface of the fracture was analysed for the tracers. The tracers were also analysed for, to a depth of up to 5 mm in the rock matrix.
The results show that there is distinct channelling in the plane of the fractures. The channels make up 5 – 20 % of the fracture. The fissure (or channel) widths are much (order(s) of magnitude) larger than what can be deduced from hydraulic testing assuming laminar flow in a smooth slit.
None of the sorbing tracers arrived at the collection points with the water. The sorbing tracer Sr migrated less than was originally expected. Cs, Eu, and U were found in highest concentrations very near the injection point. Nd and Th could not be found on the fracture surface because of the high natural background.
