The Use of Natural Uranium Decay Series Studies in Support of Understanding Redox Conditions at Potential Radioactive Waste Disposal Sites

ABSTRACTUranium is a redox-sensitive element which occurs naturally in the bedrock and groundwaters in Fennoscandia, and can be used, in conjunction with its decay series descendants, to indicate groundwater redox conditions. Not only can contemporary conditions be characterised, but evidence of past changes (e.g. during the last glaciation some 10 ka ago) can be preserved in minerals which coat the fracture walls along groundwater pathways. Uranium decay series data for groundwaters and solid fracture phases from the site of the Äspö Hard Rock Laboratory and its near vicinity are presented and discussed in the context of redox conditions.