Experimentally verified model based predictions for integrity of copper overpack: Annual report 2017

In this annual report of the project “Experimentally verified model based predictions for integrity of copper overpack” (PRECO2017) the status of the experimental and modelling activities and results has been summarised up to the end of January 2018. The testing program and related activities have been continued and partly modified to support the assessment and verification of the long term integrity of the protective copper (Cu-OFP) overpack of the canister. To consider more discontinuous uniaxial behaviour, creep tests with stepwise increasing load and stress dips were conducted, and the results were compared with those from normal constant load creep testing. In general, the transients especially from stepwise increase in loading can consume a part of the deformation capacity and shorten creep (or creep-fatigue) life. The relaxation testing programme has continued with cyclic relaxation tests. The relaxation testing aims at developing a relaxation model for the FE calculation. It is expected that with the relaxation model the stress and strain distributions will be different when compared to the FE results with a traditional creep model only. The results of continuing multiaxial (notched bar) creep testing program suggest notch weakening, or life reduction by tensile multiaxiality. The 10.000h testing of a CT specimen from the modified welding (FSW) process with argon protective atmosphere is complete and the specimen is going to be investigated by metallography to study the behaviour of the oxide particles.