Understanding the Risk of Chloride Induced Stress Corrosion Cracking of Interim Storage Containers for the Dry Storage of Spent Nuclear Fuel: Evolution of Brine Chemistry on the Container SurfaceIn the US spent nuclear fuel is likely to remain in interim dry storage until a permanent disposal solution has been developed and placed into operation. The majority of current dry storage systems consist of a welded 304 stainless steel container located within a concrete or steel overpack. The welded container serves as the primary confinement barrier protecting the fuel from the outside environment. The containers are passively cooled utilizing ambient air drawn through the overpack and across the container surface. A portion of the atmospheric aerosols carried by the air are deposited on the container surface. These include soluble salts the composition of which varies with geographic location but which is some cases are chloride bearing. With time as the canister surface cools these salts will deliquesce to form a potentially corrosive chloride-rich brine. As austenitic stainless steels are prone to chloride-induced stress corrosion cracking (CISCC) the concern has been raised that SCC may significantly impact long-term canister performance.Although the susceptibility of austenitic stainless steels to CISCC is well known uncertainties exist in terms of the environmental conditions that exist on the surface of the storage containers the electrochemical properties of the storage containers themselves and the residual stress states that will exist at the container welds. While a diversity of salts are present in atmospheric aerosols many of these are not stable when placed onto a heated surface. Given that the surface temperature of any container storing spent nuclear fuel will be well above ambient it is likely that the salts once deposited on the surface may decompose or upon deliquescence brine components may degas. This is especially true of ammonium salts common components of aerosols at inland sites. In the case ammonium chloride this results in the formation of ammonia and hydrochloric acid gasses which readily diffuse from the surface. In the case of mixed salts similar emissions are expected once deliquescence occurs. For example a mixture of ammonium sulfate and sodium chloride will upon deliquescence degas ammonia and hydrochloric acid with a precipitate of sodium sulfate left behind. Through such a mechanism chloride could be removed from the surface. To characterize this effect relevant single and multi-salt mixtures are being evaluated as a function of temperature and relative humidity to establish the rates of degassing as well as the likely final salt and brine chemistries that will remain on the canister surface.AcknowledgementsSandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation a wholly owned subsidiary of Lockheed Martin Corporation for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.