Mitigating Stress Corrosion Cracking in Spent Nuclear Fuel Dry Storage Casks

Stainless steel dry storage canisters are used to store nuclear waste. Recent work has shown that these containers are susceptible to corrosion and cracking under the environmental conditions when stored for prolonged periods. The weldments of the canisters are vulnerable to stress corrosion cracking, raising the potential for the catastrophic release of radioactive materials. We use a novel, highly effective coating system to protect the stainless-steel nuclear waste dry storage canisters. This coating system contains active corrosion inhibitors and has excellent barrier properties to prevent moisture and chloride attack. The inhibitors stop the stress corrosion cracking and pitting on stainless steels and will ensure extended corrosion protection for the life of the dry storage canisters. In the successful Phase I and II projects, we demonstrated the effectiveness of this approach in laboratory testing on stainless steel U-bends. The test pieces were sensitized to make them vulnerable to stress corrosion cracking and then coated. The U-bend testing showed that we can prevent the stress corrosion cracking of the sensitized steel and extended to the time-to-failure compared to both bare stainless (currently used on the canisters) and a control coating without our inhibitors. We also demonstrated that the coating can maintain its excellent physical properties and corrosion protection after exposure to heat and high radiation doses equivalent to at least 100 years on the canister surface. Application demonstrations and regulatory approval of this protective coating will enable commercialization of this corrosion inhibition technology. We will collaborate with a major manufacturer of dry cask storage systems, and the main designer, manufacturer, and operator of inspection robots for these systems. The ultimate goal is to apply our coating remotely to a canister section with the concrete overpack in place. We will develop and validate a remote application system for the coating and integrate this system with an inspection robot that can enter the concrete overpack and maneuver over the canister surface. The coating properties will be assessed to make sure the remotely applied coating is comparable to our current lab coatings. We will simultaneously demonstrate the ability of our coating to prevent stress corrosion cracking by performing outdoor exposure testing of bare and coated samples for at least 15 months. This procedural and performance data will support regulatory approval of the coating. This corrosion-inhibiting coating system is applicable for nuclear waste dry storage containers and can also be used for stainless steels in chemical and power plants, where stress corrosion cracking can and has caused disastrous failures to occur unexpectedly.