Grimsel test site investigation phase IV; The Nagra-JAEA in situ study of safety relevant radionuclide retardation in fractured crystalline rock, 3; The RRP project final report

Alexander, W. R.*; Frieg, B.*; Ota, Kunio 

Nagra and JAEA worked together for nearly a decade on a Radionuclide Retardation Project (RRP) at Nagra's Grimsel Test Site in Switzerland with the main aim of enhancing the understanding of radionuclide transport/retardation in fractured rock. This report summarises the results of the final phase (1996-1998) of excavation project that is an integral part of RRP. It focuses on in situ characterisation of the shear zone structure and the behaviour of radionuclides that are relevant to repository post-closure safety, but are so strongly retarded by interaction with the shear zone rock that they are not expected to migrate through the dipole flow-field in experimentally reasonable time scales. The subsequent excavation of the experimental shear zone is detailed and the results of the laboratory analysis of the three-dimensional geological structure and of the distribution of injected radionuclides within the flow-field are presented.