Mechanical performance of integrally bonded copper coatings for the long term disposal of used nuclear fuel

The preferred method for disposal of used nuclear fuel is underground emplacement in a Deep Geological Repository (DGR). Many countries have light water reactor fuels which require large Used Fuel Container or Canister (UFC) designs weighing up to 25 ton for containment. In contrast, Canada exclusively uses heavy water reactor fuel, which is substantially smaller. This has led the Nuclear Waste Management Organization (NWMO) to create a novel UFC, which uses standard pressure vessel grade steel for structural containment and a thick, integrally bonded copper coating applied to the exterior surface for corrosion protection. Currently, the coating is applied using two different methods: electrodeposition and gas dynamic cold spray. This novel copper coating needs to be fully validated to ensure adequate mechanical strength and chemical resistance for use under repository conditions. Detailed mechanical and corrosion testing programs were undertaken. Mechanical tests indicated that adhesion strengths exceeded 45 MPa and tensile properties were comparable to wrought copper. A Finite Element Model (FEM) of the copper-steel composite was created and validated using three point bend tests. This model accurately predicts the response of the composite, including large deformation and debonding failure mechanisms. Now validated, this model will be used to assess the performance of the coating on the full-scale UFC under simulated DGR loading conditions.