Mitigating Stress Corrosion Cracking in Spent Nuclear Fuel Dry Storage Casks

Stainless steel dry storage canisters DSCC are used for the storage of nuclear waste. Recent work has shown that these containers are susceptible to stress corrosion cracking under conditions that will be present underground, where a combination of chloridecontaining dusts and deliquesce leads to a concentrated aggressive aqueous environment. Under these conditions, the weldments of AISI 304/316 are vulnerable to stress corrosion cracking, a potentially catastrophic event. Better corrosion protection is required to ensure longterm safe storage of nuclear waste in dry storage casks. TDA Research will use a novel, highly effective coating system to protect the stainlesssteel nuclear waste dry storage casks. This coating system has excellent barrier properties to prevent moisture and chloride attack and also contains active corrosion inhibitors. The active inhibitors are designed to stop stress corrosion cracking and pitting on AISI 304/316 steels and will ensure extended corrosion protection for the life of the dry storage casks. In the successful Phase II project, we demonstrated the effectiveness of this approach in laboratory testing on AISI 304 stainless steel Ubends. The test pieces were sensitized to make them vulnerable to stress corrosion cracking and then coated with the protective system. The Ubend testing showed that we can prevent the stress corrosion cracking of the sensitized steel and extended to the timetofailure over both bare stainless as is used on the cask now and over a control coating without TDA’s inhibitors. The coating had excellent adhesion and resistance to boric acid. In the Phase II project we will optimize the technology and validate it for the DSCC environmental conditions. We will maximize the corrosion efficacy of our active inhibitor package and incorporate them into an advanced coating formula in collaboration with a commercial coating manufacturer. The new corrosion inhibitor coating will be rigorously tested for corrosion resistance performance, heat and radiation resistance, chemical resistance, adhesion and durability. Finally, we will demonstrate application of our coating on a dry storage canister. This corrosioninhibiting coating system is applicable for nuclear waste dry storage containers and can also be used for austenite stainless steels in chemical and power plants. Stress corrosion cracking can cause disastrous failure to occur unexpectedly, even with a minimal overall loss of material.