Director. Additionally, PNNL recognizes Mr. Tom Sowinski as the DOE Technical Manager and Mr. Carl Sink as the HQ Program Director. PNNL would like to thank Mr. Grandy for his guidance and technical direction throughout the course of this effort. The Technical Team would also like to thank our colleagues at ANL for working jointly with PNNL staff over the course of this collaborative effort. At PNNL, the authors wish to thank Ms. Katie Holton for her coordination and support of PNNL project logistics and for her help in handling travel-related reporting. The Team is indebted to Mr. Royce Mathews (also a co-author on this TLR) for providing in-Lab support across the entire spectrum of technical activities conducted on this project. In addition, the Team would like to express their thanks to Mr. Clyde Chamberlin, who was very responsive to our needs as we required his expertise in developing and employing an effective procedure for polishing the faceplate of the prototype probes, prior to insodium testing. The Team would also like to extend their gratitude to Ms. Lori Bisping for all of her hard work in providing administrative and financial reporting support to this project. Working with the PICS system can be challenging, and Lori's expertise and efficiency are second to none. Finally, the PNNL technical team would like to extend their thanks to Ms. Kay Hass for her ongoing support, attention to detail, and technical editing expertise in preparing and finalizing this Technical Letter Report.

In this effort, an assessment of bulk ultrasonic (UT) and eddy current (ECT) methods and techniques is performed for inspecting the surfaces of dry cask storage systems (DCSSs) canisters. Some DCSS canisters (especially those located in coastal environments) will be exposed to environmental conditions, which can cause atmospheric stress corrosion cracking (SCC). Information collected from the field and from laboratory studies has not been able to rule out the possibility of atmospheric SCC in DCSS canisters, although no occurrences of atmospheric SCC in DCSS canisters have been detected. UT and ECT methods and techniques are already used to inspect nuclear power plant components and this experience, along with their relative maturity, makes these methods and techniques likely frontrunners for near-term application to examination of dry storage canister surfaces. In this report, the results of several performance reliability studies for UT and ECT are reviewed. The detection, depth-sizing, and lengthsizing results are documented and summarized to quantitatively estimate the adequacy of UT and ECT for inspecting dry storage canister surfaces. In addition, this effort focuses on the implementation of NDE methods and techniques in the Holtec HI-STORM 100 system and the Transnuclear NUHOMS horizontal storage modules and considers environmental compatibility, accessibility constraints, and NDE sensor deployment options for these systems.v

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