Materials Aging Issues and Aging Management for Extended Storage and Transportation of Spent Nuclear Fuel (NUREG/CR-7116, SRNL-STI-2011-00005)
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Manuscript Completed: September 2011
Date Published: November 2011
R. L. Sindelar, A.J. Duncan, M.E. Dupont, P.-S. Lam,
M.R. Louthan, Jr., T.E. Skidmore
Savannah River National Laboratory
Aiken, SC 29808
R.E. Einziger, NRC Technical Project Manager
NRC Job Code J5657
Office of Nuclear Material Safety and Safeguards
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
An evaluation of potential degradation of materials in the Systems, Structures, and Components (SSCs) of dry cask storage systems (DCSS) for Independent Spent Fuel Storage Installations (ISFSIs) has been performed to identify issues in the technical bases for regulating storage well beyond the present allowable storage time of 120 years that includes 60 years pool storage and 60 years dry storage. The evaluation included low (≥45 GWd/MTU) and high burnup (HBU) (> 45 GWd/MTU up to approximately 62.5 GWd/MTU) fuel, and was performed to determine if: 1) degraded conditions could be anticipated to develop in the materials of the SSCs over an extended storage and transportation (EST) period (> 120 years); and 2) the anticipated degradation would challenge functions important to safety during storage and during post-storage transportation including fuel retrieval for final disposition.
The approach followed a general Aging Management Review process by: 1) identifying the materials of construction of the SSCs; 2) evaluating their susceptibility to degradation from environmental conditions of exposure; and 3) evaluating the potential for degradation to impact the safety functions required by the present Code of Federal Regulations for dry storage systems and spent fuel transportation in 10 CFR Part 72 and 10 CFR Part 71, respectively. The evaluation was performed using extrapolation of available data and materials degradation models with consideration of service histories of similar materials systems, and with expert judgment.
With the present materials systems and controls for a DCSS, no materials degradation phenomena were identified that would be expected, with certainty, to be operative and cause an impact sufficient to violate the safety functions for storage and transportation. However, several data/information/technology gaps were identified that would require resolution to provide a sufficient technical basis to demonstrate the continuing integrity of the SSCs and their ability to maintain functions important to safety throughout EST.
Recommendations for activities to resolve the potential materials aging issues are provided. Aging management activities for preventive maintenance and periodic condition assessments through inspections of SSCs are outlined. Additional recommended activities include materials testing and a full cask demonstration project under conditions that challenge the SSCs of the DCSS to verify the expected materials’ behavior and provide confidence that the SNF, as is presently conditioned and dry-stored, can continue to be safely stored for greater than 120 years, and handled and transported following storage.