Copper canisters for storage of nuclear waste will be exposed to creep. The canisters will be closed with friction stir welding (FSW). To describe the creep behaviour of the welds, uniaxial creep tests have been performed. A previously developed fundamental creep model for parent metal is applied to the different weld zones. The differences in microstructure and yield strength between the weld zones are taken into account. Creep strain versus time curves for the weld zones have successfully been predicted without the use of any adjustable parameters. It should be noted that the temperature range of interest of 50–100°C is deep down in the power law break down regime with Norton exponents between 25 and 100. The constitutive equations are used in FEM computations of creep in the canister weldments.