Natural analogue evidence for controls on radionuclide uptake by fractured crystalline rock

Fractured Crystalline Rocks (FCR) are being considered in several countries as hosts for radioactive waste repositories. In FCR, radionuclides may be transported relatively rapidly by bulk groundwater flow through open fractures, but much more slowly diffusion porewater the rock matrices. Rock matrix (RMD) is of aqueous phase, between fractures and Sorption or co-precipitation on fracture surfaces walls pores causes further radionuclide retardation. RMD important a repository's safety case has been investigated many published short-term (to few years) laboratory in-situ experiments. To improve understanding over longer timescales, we evidence natural radioelements, radioelement analogues, five exemplar fractured crystalline samples aged c. 70 Ma 455 Ma. The sample suite consisted two Borrowdale Volcanic Group (BVG) meta-tuff from northwest England, Carnmenellis Granite southwest England Toki central Japan. Uptake loss studied elements limited to an altered damage zone each sample, coupled mineral alteration processes. These zones most extensive (a tens millimetres) samples. We also found unstable primary igneous minerals persist immediate wallrocks granite samples, suggesting that were not permanently water saturated these Although only small was studied, results show while some kinds others it negligible. Site-specific information therefore needed determine how reliance can placed when developing case.