2014:08 Technical Note, Review of Long-Term Redox Evolution of Groundwater and Potential Influence of Oxygenated Glacial Meltwater in SR-Site

The Swedish Radiation Safety Authority (SSM) is reviewing an application submitted by the Swedish Nuclear Fuel and Waste Management Company (SKB) in 2011 to construct, possess, and operate a deep geologic repository for spent nuclear fuel at the Forsmark site in the municipality of Östhammar, Sweden.  SKB has presented details of its long-term safety assessment, SR-Site, in a main report (SKB, 2011, TR-11-01) and in multiple supporting technical documents that are cited by the main report.  In developing the safety case for SR-Site, SKB identified the presence of reducing conditions in groundwater as an important safety function that contributes to the optimum performance of the disposal system.  SKB stated that a fundamental requirement for the barrier effect provided by the copper canister is to avoid corrosion of the canister by oxygen. SKB also identified reducing groundwater conditions as a safety function related to the retardation of radionuclides with respect to maintaining a low dissolution rate for spent nuclear fuel in contact with water, low elemental solubilities of certain radionuclides, and high sorption coefficients (Kd values) for certain radionuclides.

The objective of this technical review is to determine if SKB’s representation of future redox conditions in a deep geologic repository at the Forsmark site is defensible and whether there are factors unaccounted for in SKB’s analysis that may significantly alter the range of represented conditions. The review examined the basis for SKB models for long-term redox evolution of groundwater at the Forsmark site, with an emphasis on the potential ingress of oxygenated glacial meltwater to repository depth.  Key considerations were the adequacy of SKB data for the intended application, the validity of the SKB models for redox evolution, and the adequacy of SKB’s conceptual understanding and treatment of uncertainties