This paper describes development and demonstration of nondestructive examination (NDE) technologies to support periodic examinations of interim dry storage system (DSS) canisters for spent nuclear fuel in the USA to verify continued safe operation and that the canister confinement is intact and performing its intended safety function. Specifically, this work relates to NDE technology development for "canister" based DSS systems, which form the majority population of DSSs in the USA for interim storage of spent nuclear fuel. Consideration of potential degradation of the welded stainless-steel canister in these systems is required for continued usage in the period of extended operation (PEO) beyond the initial license or certified term. Physical access to the canister surface is constrained due to narrow annulus spaces between the canister and the overpack, tortuous entry pathways, and high temperatures and radiation doses that can be damaging to materials and electronics related to inspections. Several activities to demonstrate NDE technologies for the inspections of different DSS systems are summarized.

This paper presents efforts to overcome challenges with empirical probability of detection (POD) estimations in the nuclear power industry through the utilization of a novel virtual flaw method. A virtual round robin (VRR) study was conducted under the Program for Investigation Of NDE by International Collaboration (PIONIC), organized by the United States Nuclear Regulatory Commission (NRC) utilizing data generated by the virtual flaw method. Analysis of results from the VRR was performed by teams from Pacific Northwest National Laboratory (PNNL), Electric Power Research Institute (EPRI), and Aalto University. Empirically derived POD estimations are presented, and challenges associated with obtaining these estimations are discussed. The virtual flaw method is introduced and some details of its implementation for the VRR activity are described. Results from POD analysis of the VRR data by PNNL, EPRI, and Aalto University are presented and a discussion regarding differences in analysis results is provided. Finally, potential future efforts to improve the application of the virtual flaw method and its estimation of POD are discussed.

This paper describes development and demonstration of remote crawling systems to support periodic examinations of interim dry storage system (DSS) canisters for spent nuclear fuel in the USA. Specifically, this work relates to robotic crawler developments for "canister" based DSS systems, which form the majority population of DSSs in the USA for interim storage of spent nuclear fuel. Consideration of potential degradation of the welded stainless-steel canister in these systems is required for continued usage in the period of extended operation (PEO) beyond their initial licensed or certified terms. Challenges with performing the periodic examinations are associated with physical access to the canister surface, which is constrained due to narrow annulus spaces between the canister and the overpack, tortuous entry pathways, and high temperatures and radiation doses that can be damaging to materials and electronics. Motivations for performing periodic examinations and developing robotic crawlers for performing those examinations remotely will be presented, and several activities to demonstrate robotic crawlers for different DSS systems are summarized.

The U.S. Nuclear Regulatory Commission (NRC) in cooperation with the nuclear industry has developed a probabilistic fracture mechanics code called xLPR (extremely Low Probability of Rupture). xLPR is a modular-based probabilistic assessment tool for determining probability of leakage and rupture for pressure boundary piping. One of the modules in xLPR is the In-Service Inspection (ISI) module which models the probability of detection (POD) and sizing performance of NDE performed during in-service inspection to account for and predict the influence of periodic inspections on the probability of component leakage and rupture. The accuracy of the ISI module in xLPR is dependent on the quality of the estimates of detection and sizing performance that are input to the module. Multiple efforts have been attempted to quantify the detection and sizing performance of NDE in the nuclear industry. These efforts include an analysis of inspection data collected as part of the industry’s Performance Demonstration Initiative (PDI) and data collected from NRC sponsored round robin studies such as PINC-Program for the Inspection of Nickel Alloy Components and PARENT-Program to Assess the Reliability of Emerging Nondestructive Techniques. Usage of a given data set in the xLPR ISI module requires understanding of which set of data is most representative for the specific scenario under consideration. A comparative analysis of detection performance data from PDI, PINC, and PARENT is provided in this paper in an effort to elucidate for users of xLPR types of applications the above mentioned data sets may be most appropriate for.

Welded stainless steel canisters are used in dry storage systems of spent nuclear fuel from commercial power reactors in the U.S. These systems were initially licensed for 20 years and may receive license renewals for 40 more years from the U.S. Nuclear Regulatory Commission (NRC). The requirements for license renewal include aging management programs (AMPs) to ensure systems, structures, and components (SSCs) continue to perform their safety function. Nondestructive examination (NDE) plays an important role in AMPs that rely on inspection to detect service degradations such as chloride-induced stress corrosion cracking (CISCC) of austenitic stainless steel canisters so that mitigation actions can be taken to manage the aging effects. The American Society of Mechanical Engineer (ASME) is currently developing a code case for the in-service inspection (ISI) of dry storage canisters. The nuclear industry is also developing inspection systems for conducting examinations of canisters. This paper is intended to summarize the on-going efforts to develop inspection systems and to evaluate the effectiveness of inspection systems to access the canister and detect flaws. This paper also documents efforts by Pacific Northwest National Laboratory (PNNL) to develop CISCC flaws on stainless steel specimens in an attempt to compare NDE responses to simulated flaws to assess the impact of flaw characteristics on the NDE performance.