Study of creep in annealed copper with slow strain rate tensile tests

In Sweden it is planned to use copper canisters for depositing nuclear fuel waste at a depth of 500 metres in the bedrock. As a corrosion barrier, the copper canister must be of very high quality and remain intact for 100,000-year. In the repository the copper material will be deformed by creep. Up to 5% creep strain will occur at 75-90ºC. The copper must be able to withstand this deformation. To study this phenomenon, extensive conventional creep testing has been performed. It has also turned out that slow strain rate tensile tests are quite valuable and it is now proposed that new test series are performed.

Low oxygen copper with about 50 ppm phosphorous will be used throughout the tests. The strain rates will be between 10-7 and 10-3 s-1. The temperatures will be chosen as 20, 75, 125 and 175ºC. The tests will be performed in a newly developed test machine with modern software.

For a few selected specimens, in particular those at low strain rates, light optical microscopy will be carried out The main task of the metallography is to verify that the cavity formation is consistent with that in previous creep tests.

The graduation thesis will be performed at the department of Materials Science and Engineering, KTH during a period of 5 months. The work will take place in close collaboration with SKB (The Swedish Nuclear Fuel and Waste Management Corporation). Prof. Rolf Sandström will act as supervisor.