The performance of PLUS7 for grid to rod fretting

Fuel and fuel assembly components, resulting in degradation and unexpected failures by a variety of mechanisms, have been challenged by power up-rates, longer cycles, and higher fuel duty and discharge burnup. GTRF1 is the predominant fuel failure mechanism in the U.S. Therefore, U.S. is trying to mitigate GTRF failures. As such efforts, new fuel designs, pool side assembly repairs, fuel management, and coolant flow paths have been implemented or changed. Despite significant efforts, it is apparent that GTRF failures still occur and jeopardize the defect-free. With this experience, efforts are still needed to understand the fundamental and synergistic mechanisms and their relative sensitivities to GTRF failures to further develop mitigation and define margins. Materials and designs of fuel cladding and assembly components, grid-to-rod clearance, and flow-induced vibration are all major variables to GTRF failures This current understanding is rather qualitative and thus experimental and post-irradiation examinations and more-detailed modeling are needed to quantitatively assess various parameters that contribute to GTRF induced failures. As such activities, EPRI contracted to KHNP. The contract name is 'Margin assessment of PLUS7 Fuel for GTRF mitigation'. This paper describes the results of the project. It is an initial effort to conduct a margin assessment of advanced fuel designs for mitigation of GTRF. A Lead Test Assembly (LTA) of the 16 x 16 PLUS7TM fuel design manufactured by Korea Nuclear Fuel (KNF) was discharged in 2007 after three cycles in Ulchin-3 (UCN-3) and was examined in the hot cell at the Korea Atomic Energy Research Institute (KAERI).