Development of cold spray technology for copper coating of carbon steel used fuel container prototypes for CANDU fuel

The NWMO, in collaboration with the National Research Council (NRC), is investigating the use of cold spray technology to copper coat the NWMO proposed carbon steel Used Fuel Container (UFC) dedicated to the storage of used CANDU fuel in a Deep Geological repository (DGR). Copper coating is applied to the external surfaces of UFCs for corrosion protection. In this report, a summary of the preliminary research and development program activities to assess the viability of using the cold spray technology is presented. Results from the tests are documented and applied to demonstrate and optimize the application of copper coating on a full-scale UFC prototype. Research to date has included the different tasks required to successfully apply copper coatings of various thicknesses on steel substrates of varied dimensions: from small coupons for corrosion studies to larger pieces for mechanical tests, key geometric parts of the UFCs such as the hemispherical heads, and a full-scale UFC prototype, including its weld closure. Activities involved: (i) powder selection, (ii) general coating development, (iii) UFC coating optimization, and (iv) prototyping. Reference spraying and annealing conditions were established and coating quality and properties were validated on different substrate geometries and compositions. Results also indicated that powder manufacturing and robust handling procedures are key considerations for reliability and consistency of coating properties. A clear path to manufacturing copper coatings on UFCs via cold spray deposition was developed, including details on (i) process parameter scale-up adjustment, (ii) spray set up and pattern development, (iii) coating joining procedure, and (iv) coating machining. The program was successful in demonstrating the potential use of cold spray technology for the protection of UFCs by achieving the manufacture of a full-scale prototype to NWMO specifications. However, further extensive validation work will be required prior to the implementation of cold spray coatings for UFC manufacture. (author)