Relaxation of OFP copper

Oxygen-free phosphorus-doped (OFP) copper is a prime candidate outer shell (overpack) material to protect the spent fuel canisters against corrosion in the underground repository. As the canister and its copper shell are subject to internal heating by residual activity of the contents, it is possible that with sufficient loads or strains from e.g. thermal, handling or other sources shell will creep to some extent. In this work the isothermal uniaxial relaxation behaviour of OFP copper is considered from the point of view of basic relaxation modelling and experimental model validation. Validation is considered necessary before extending the modelled relaxation behaviour to multi-axial cases and finite element analysis (FEA) of the canister (overpack) details. The initial candidate relaxation models were selected for the expected performance at relatively low temperatures and likely tolerance of transients when implemented to FEA. The initial experiment however shows little difference between the selected models, and further testing appears necessary. Nevertheless, classical relaxation models appear to provide fair agreement with to the observed low temperature relaxation in OFP copper