2018 | AFC ACCOMPLISHMENTS 92 Modified Burst Testing of ATF Cladding Materials Principal Investigator: M. Nedim Cinbiz Collaborators: N.R. Brown, R.R. Lowden Jr., M. Gussev, K. Linton, K.A.Terrani Accident tolerant fuel (ATF) cladding candidates must maintain or extend the safety envelope of current light-water reactors (LWRs) not only during severe accident conditions, but also during postulated design-basis accidents, such as a reactivity-initiated accident (RIA). During an RIA, the removal of the control rods from the LWR’s core causes a prompt increase of the fission- rate density until the reactor is shut down.The deposited energy in the fuel increases the fuel temperature, which causes fuel thermal expansion. If the fuel and cladding are in contact before or during the RIA, this expansion imposes a mechanical deformation on the cladding’s inner surface.This interaction, termed the pellet-cladding mechanical interaction (PCMI), occurs in milliseconds. During an RIA, cladding deformation may surpass the design limits of future ATF-installed LWRs.To address this issue, this study investigates the mechanical response of ATF cladding candidates under PCMI- like conditions over RIA time scales. Figure 1. (a) Schematics of the novel optical metrology technique, including a camera, a telecentric lens system, and first-surface mirrors. (b) Projections of SiC/SiC composite sample on the camera. The sample was dyed with black and white paint to create speckle patterns. (c) A schematic of the MBT for the PCMI-type loading.