In Sweden spent nuclear fuel is planned to be placed 500 m down in the bedrock. The spent nuclear fuel will be contained in copper canisters. The reason behind the selection of copper is its thermodynamic stability against corrosion in the depository. The copper will be exposed to mechanical loading and will be plastically deformed due to creep. The canisters will be sealed by friction stir welding. Since the canisters have to survive intact for many thousands of years, the properties of the welds are critical. Oxygen free P-doped copper (Cu-OFP) is selected for its excellent creep ductility properties and corrosion resistance. In this thesis work creep ductility behavior of friction stir welded copper chosen at different areas of the weld is evaluated by using the test slow strain rate tensile test. Samples are chosen at different weld areas namely weld, cross weld and HAZ. A sum of 21 specimens is tested. These tests are achieved at three various strain rates and each rate are carried out at three different temperatures. The strain rates used for tests are 1e-4, 3e-6 and 1e-7 [1/s]. The samples are strained until rupture, 20% and 5% of the gauge length. Yield strength and tensile strength are usually decreasing with increasing temperature and at higher temperature the material can be easily deformed. Few strange behaviors are also observed for the samples from HAZ areas at strain rate 1e-7[1/s]. The experimental results are justified by using the Knock-Mecking model. The parametersand ω were evaluated by curve fitting method.

Materials intended for disposal of spent nuclear fuel require a particular combination of physical and chemical properties. The driving forces and mechanisms underlying the material’s behavior must be scientifically understood in order to enable modeling at the relevant time- and length-scales. The processes that determine the mechanical behavior of copper canisters and iron inserts, as well as the evolution of their mechanical properties, are strongly dependent on the properties of various defects in the bulk copper and iron alloys. The first part of the present thesis deals with precipitation in the cast iron insert. A nodular cast iron insert will be used as the inner container of the spent nuclear fuel. Precipitation is investigated by computing effective interaction energies for point defect pairs (solute–solute and vacancy–solute) in bcc iron using first-principles calculations. The main considered impurities in the iron matrix include 3sp (Si, P, S) and 3d (Cr, Mn, Ni, Cu) solute elements. By computing interaction energies possibility of formation of different second phase particles such as late blooming phases (LBPs) in the cast iron insert is evaluated. The second part is devoted to the fundamentals of dislocations and their role in plastic deformation of metals. Deformation of single-crystal copper under high strain rates is simulated by employing dislocation dynamics (DD) method to examine the effect of strain rate on mechanical properties as well as dislocation microstructure development. Creep deformation of copper canister at low temperatures is studied. The copper canister will be used in the long-term storage of spent nuclear fuel as the outer shell of the waste package to provide corrosion protection. A glide rate is derived based on the assumption that at low temperatures it is controlled by the climb rate of jogs on the dislocations. Using DD simulation creep deformation of copper at low temperatures is modeled by taking glide but not climb into account. Moreover, effective stresses acting on dislocations are computed using the data extracted from DD simulations. / <p>QC 20170428</p>