2014:43 Technical Note, Workshop on general corrosion of copper

This report describes the outcome of the workshop organized by SSM on general corrosion of copper that was held in Stockholm on the 26-27th of August, 2013. The report summarizes the issues discussed and extracts the essential viewpoints that have been expressed. It should not be considered as a comprehensive record of all the discussions at the workshop and individual statements made by workshop participants should be regarded as opinions rather than SSM’s point of view.

Based on the information, arguments and analyses presented in the workshop, it has been concluded that no safety-significant impacts on the general corrosion rate of canisters or the number of canisters failing by corrosion are clearly evident for either intact buffer or eroded buffer situations. The reason for the absence of sensitivity to possible erosion of buffer arises from several factors, most notably from the assumed application of criteria for the rejection of deposition-holes (i.e., rejecting holes with high groundwater inflow rates from fractures). 

Low erosion rates would be another mitigating factor regarding the safety-significance of any impacts for the eroded buffer case, especially where extreme speculative alternative models or combinations of alternative models are considered.  These erosion rates are expected to be extremely low for the currently reported distributions in fracture flow rates and fracture apertures at Forsmark.  Therefore, significant buffer erosion to allow advective flow conditions would only occur in a few deposition holes during a far-future glaciation, at a time when the radioactivity of the spent fuel will have greatly decreased.