Adaptation: The Key to Successful Interim Storage is Anticipating Change

Historically, engineering structures have been in use far beyond their original intended life-spans. One particularly notable example is the Eiffel Tower in Paris, France, which was originally intended to be dismantled after 20 years, but still stands 124 years after it was constructed. In the United States, dry storage systems (DSSs) for spent nuclear fuel have been renewed for 20 years beyond an initial 20-year licensing period. Since 2011, the initial and renewal license terms of DSSs have been increased up to 40 years. Similar to the Eiffel Tower, these passive structures were intended to be used for a set time period, but have been successfully operated for time periods longer than planned. DSSs, which are required to meet regulatory requirements regarding criticality, containment, shielding and fuel retrievability, may include materials that have the potential for degradation or potential failure over an extended time span. Continued safe and successful operation of DSSs require an effective aging management program, which includes inspection, maintenance, and mitigation of potential age related degradation of the systems, structures, and components important to safety. Therefore, designers should consider designs and materials that anticipate degradation of these systems and components to ensure adequate protection of the public and the environment over extended storage time frames. This paper discusses a potential adaptive approach to DSS design that allows for inspection, maintenance, and mitigation of DSS material degradation. This approach does not rely on fuel geometry for criticality control, rather it allows for fuel reconfiguration under the assumption that the fuel cladding degrades by some unidentified mechanism over an extended time frame. This adaptive approach (which may require changes in regulatory requirements) also proposes that the canister (not the fuel assemblies) is the retrievable waste form and emphasizes the advantages of designing contingency containers ready for fabrication immediately prior to canister shipment if canister damage or degradation warrant. Finally, additional considerations for more robust overpack designs that permit easier inspection of the overpack and canister are discussed. The views expressed herein are those of the author and do not constitute a final judgment or determination of the matters or the acceptability of any licensing action that may be under consideration by the U.S. Nuclear Regulatory Commission. (author)