Development and Implementation of an In-situ Repair Method for ISFSI Canisters - 21028

A remote, robotic method for mitigation of damage to an Independent Spent Fuel Storage Installation (ISFSI) canister has been developed and successfully tested at San Onofre Nuclear Generating Station (SONGS). It is currently ready for implementation in a vertical system if required will be ready in 2020 for implementation in a horizontal canister system if needed. The project was in response to a State of California Coastal Commission requirement to demonstrate a canister repair technology at SONGS. There is currently no degraded canister requiring the use of this technology. It is developed purely as a mitigation strategy. Southern California Edison (SCE) is the primary owner/operator of SONGS. SCE made the decision in 2017 (check date please) to proactively manage and fund a project to develop the mitigation strategy discussed here to address the Coastal Commission Requirement. SCE chose WDPMS to lead the effort. Development of the robotic system included miniaturizing existing metallic overlay technology and combining it with robotics previously used at SONGS for inspection. The metallic overlay process (also known as 'cold spray') is a mature technology. However, it had to be miniaturized and optimized for use at SONGS. This paper provides details on the development, testing and on-site implementation of the robotic overlay system. The background leading to the development of the process will be discussed. The development of ASME Code Case N-860[1], which would provide guidance in decision making for implementation of the Metallic Overlay process is also included Mitigation methods were initially researched by EPRI, and several projects funded by the Department of Energy's Nuclear Energy University Program (NEUP) are on-going. However, a fully developed mitigation method, which would allow in-situ repair of a loaded fuel canister was not available prior to the SONGS project. It is considered highly unlikely that significant degradation requiring mitigation would occur during the initial license period (approximately 20 years) of loaded spent fuel canister operation. A renewed license for spent fuel storage canister operation (after the initial 20-year period) requires the implementation of an Aging Management Program for the loaded fuel canisters, which includes periodic visual inspection requirements of selected canisters. There have been several ISFSI canister systems which have been granted renewed licenses. As part of the renewals, several canisters have been visually inspected across the United States, with all canisters in very good condition, and none requiring mitigation. The inspection results are consistent with the conclusions of NUREG-2214, 'Managing Aging Processes In Storage (MAPS) Report', published in 2019, which analyzed potential canister (and ISFSI System) degradation methods over 60 years of operation, and provides guidance for the future licensing, operation, and inspection of ISFSI systems long term. The metallic overlay process has been developed in advance of a specific need. It is a proactive measure intended to allow efficient response in the event that mitigation is required at San Onofre. (authors)