Executive summary of phase 2

The second phase of the Stripa project included the continued development of methods and techniques for repository site investigations. The crosshole investigations demonstrated that it is possible to characterize fractures in crystralline rock with a reliability and realism not obtained before. At the investigated site at Stripa, it was shown that groundwater flow is concentrated within a few major fractures that were idenfified by geophysical methods. The work at Stripa has shown that it is possible to collect and analyze data that enable one to determine the type of distribution and its parameters for each of the essential geometrical and hydraulic properties of the fracture system, and hence compare one site with another as part of experience builing in safety assessment studies. The migration experiment demonstrated that the groundwater flow could be very unevenly distributed in the rock. The hydrogeochemical investigations at Stripa also indicated that a new type of solute source must be considered - fluid inclusions in the host rock. The age of the solutes may be entirely different from the age of the groundwater. Sealing and redirection of the groundwater flow away from man made openings in the rock was tested at Stripa and found to be feasible as shown in the various plugging and sealing experiments. The use of Na bentonite in the form of suitably shaped blocks of highly compacted powder has been found to be very practical for sealing off boreholes, shafts and tunnels in repositories