Background
The Swedish Radiation Safety Authority (SSM) reviews the Swedish Nuclear Fuel Company’s (SKB) applications under the Act on Nuclear Activities (SFS 1984:3) for the construction and operation of a reposi-tory for spent nuclear fuel and for an encapsulation facility. As part of the review, SSM commissions consultants to carry out work in order to obtain information on specific issues. The results from the consultants’ tasks are reported in SSM’s Technical Note series.
Objective
This project is part of SSM:s review of SKB:s license application for final disposal of spent nuclear fuel. The assignment concerns review of creep mechanisms for copper material used for corrosion barrier in canisters for final disposal of nuclear fuel in Sweden. This work is a continuation of an earlier work in 2010-2011 reported in SSM Technical Note 2012: 13.
Summary by the author
In a previous report, SSM Technical Note 2012:13, it was concluded that SKB has presented insufficient evidence to justify their position that the phosphorus alloyed oxygen free (OFP) copper has an adequate creep ductility during long term storage. This conclusion was based on a study of grain boundary sliding in both OF and OFP copper, which showed that the basis for the SKB theory on creep brittleness, necessary for extrapolation to storage conditions, was wrong. Recently SKB has attempted to invalidate the results of the grain boundary sliding study but in the present report it has been shown that the results for oxygen free (OF) copper are consistent with SKB’s theory (which is calibrated against their results for OF copper). In the author’s view, this implies that SKB has presented insufficient explanation for why OFP material, despite having the same amount of grain boundary sliding as OF copper, remains ductile under conditions when OF behaves in a brittle creep manner. Therefore the previous conclusion stands.