51316-7653-Understanding the Risk of CISCC of Interim Storage Containers for the Dry Storage of Spent Nuclear Fuel: Residual stresses in typical welded containers

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Product Number: 51316-7653-SG

ISBN: 7653 2016 CP

Author: David Enos

Publication Date: 2016

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Understanding the Risk of Chloride Induced Stress Corrosion Cracking of Interim Storage Containers for the Dry Storage of Spent Nuclear Fuel: Residual Stresses in Typical Welded ContainersIn 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.While 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. Evaluation of the residual stresses present in typical storage systems is being conducted on a full scale mockup produced late in 2014. Designs from the three primary vendors in the US for welded stainless steel interim storage systems (Areva-TN Holtec and NAC) were reviewed to determine materials and methods of construction and a single canister design was selected. A cylinder (without end plates) was produced replicating the TransNuclear NUHOMS 24P design. This container design is employed at the Calvert Cliffs nuclear power station which was the first site surveyed by EPRI to determine the dust composition on the surface of the containers (Gellrich 2013). Deep-hole drilling the contour method and x-ray diffraction are being used to characterize the stress distributions for the mockup welds.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.