b'2.2 LWR CORE MATERIALSMicrostructure Evaluation of Pre and Post LOCA HBu FuelPrincipal Investigator: Rachel L. SeibertTeam Members/ Collaborator: Nathan Capps, Casey McKinney, Chad Parish, Tyler Gerczak, Jason Harp, Jesse WerdenFigure 1. Optical micrographs of two fuel rods under examination (a) as-irradiated and (b) post-simulated LOCA testing. Fuel fragmentation is clearly observed in the before and after, and the different radial zones of the HBu structure are also observableas observed under SEM following thermal etchingH igh burnup (HBu) fuel rodsindicate microstructure and fission using uranium dioxidegas release play a role in HBFF, under loss-of-coolantas experimental results indicate accident (LOCA) testing present aFission Gas Release (FGR) leads to phenomenon known as fuel frag- fuel fragmentation and pulverization. mentation relocation and dispersalTo better understand the role micro-(FFRD), in which LOCA-tested fuelstructure plays in HBFF, advanced with sufficiently HBu suffer frag- microscopy techniques are used mentation and pulverization. Alsoto assess HBu fuel before and after called high burnup fuel fragmenta- simulated LOCA testing.tion (HBFF), pulverized fuel results in a sand-like consistency and couldProject Description:prove dangerous due to its ability toCommercial UO 2fuel rods before relocate into the cladding balloonand after simulated LOCA testing region of the fuel and potentiallywere explored using advanced disperse from cladding undermicroscopy. Samples were selected rupture conditions. Previous engi- material irradiated in the North neering scale studies determinedAnna powerplant and experienced cladding behavior, pellet history,average burnups greater thanand LOCA test conditions all directly63 GWd/tU. Different burnup struc-impact pulverization severity, but dotures were observed across the radial not explain the mechanism drivingcross sections of the fuel. Scanning pulverization. Additional studieselectron microscopy (SEM) was 26 2022|AFC ACCOMPLISHMENTS'