Part 2 of 2 Parts (Please read Part 1 first)
      The construction of a spent nuclear fuel storage canister begins with a flat piece of stainless steel that is rolled into a cylinder and then welded where the edges of the flat piece join. The heat from the welding process creates zones in the seam that experience tensile stress. Stress on these zones around the weld seam makes the seam more susceptible to corrosion from salt over time.
     Sandia received its test canisters on November 13th. Each of them will be outfitted with thirty-two electrical heaters to simulate the heat released as a result of radioactive decay. Thirty-two heating elements are used because the typical storage canister contains thirty-two spent nuclear fuel assemblies which are bundles of fuel rods. Devices called thermocouples which measure temperature and other sensors for diagnostic testing and surface sampling will also be attached to the canisters. 
     Once the setup and tests at Sandia are complete, the canisters will be repacked for shipment to a storage pad at an independent fuel storage facility on the West Coast. There the canisters will be subjected to the same real-life conditions of canisters that are currently in use.
     The Sandia team is led by managers Sylvia Saltzstein and Geoff Freeze, Durbin and includes chemists/corrosion specialists Charles Bryan and Rebeca Schaller. They will be joined by scientists from other national laboratories to monitor the test canisters and record surface deposits for three to over ten years depending on how much variation there is in the data as time passes. Durbin said, “Sodium-chloride, or salt, that settles on the surface of spent nuclear-fuel canisters can lead to chloride-induced stress corrosion cracking, and right now there is inadequate data on these surface deposits.” 
     Durbin said that in real-life storage of nuclear waste in canisters, the decay heat generated by the spent nuclear fuel creates natural convection currents around the canisters which causes outside air to be drawn across the surface of the canisters. These convection currents help to cool the spent nuclear fuel over time. As the ambient air around the canisters is drawn in, salt and other particulates in the air are pulled in as well. They can settle on the canister surface. During the Sandia tests, the electrical heaters installed inside the canisters will replicate the decay heat driven convection process without the need for real nuclear materials.
     In hot and dry conditions, salt deposits alone will not cause any serious issues. However, over time, as the level of decay heat falls and the canisters cool, water can condense on the surface of the canister and a brine can form. Durbin said, “These conditions can occur nationwide and are seen as precursors to chloride-induced, stress-corrosion cracking. Back when these canisters were being designed, people weren’t thinking about this as an issue because we had a plan for permanent disposal. The current national nuclear waste situation forces canisters to be stored onsite for the foreseeable future, which could be 100 years or longer, so stress corrosion cracking becomes more of a concern.”
     In addition to the long-term heating and surface deposition tests, the researchers at Sandia will also utilize another three canisters for tests in the laboratory to conduct research on the cracking that can be caused by salt and stress. This research will focus on the welded seams and intersections of the canisters. The effectiveness of commercially available crack repair and mitigation coatings will be tested. In order to test the seams, the team will slice the canisters into small pieces and test pieces with and without welded seams to study the precursor conditions of salt and stress to cause corrosion that results in the formation of cracks.