b'In-Pile LOCA Testing at TREATPrincipal Investigator: Robert ArmstrongTeam Members/ Collaborators: Colby Jensen, Charles Folsom, Nicolas Woolstenhulme, Devin Imholte, and Changhu XingThe TREAT TWIST deviceI n recent years, the U.S. nuclearclosely with industry and national energy industry has set goals forlaboratory researchers, the fuel life is designed to be thelicensing fuel burnup beyondhistory and corresponding micro-future LWR fuel safetycurrent limits of 62 GWd/t [1],structure as well as the specific LOCA testing device with world- targeting up to ~75 GWd/t. Industryconditions of relevance have been a leading, unique capabilityhas identified Loss of Coolant Accidentmajor focus for guiding design. In to investigate high(LOCA) performance of high burnupparticular, the fuel conditions related burnup fuel performancefuel, in particular fuel fragmentationto potential rod failures occur shortly during LOCA (FFRDrelocation and dispersal (FFRD), asafter the blowdown event with a behaviors) supportingan issue requiring additional researchcladding heat up rate driven largely industry goals to achieveand development (R&D) support.by relatively high stored energy in the burnup extension. Additionally, the closure of the Haldenfuel, a more dynamic condition than research reactor has left no possibili- has ever been evaluated via integral ties for in-pile LOCA testing. Workingexperiments previously. Therefore, the Advanced Fuels Campaign (AFC) is developing in-pile LOCA testing capabilities in the Transient Reactor Test Facility (TREAT) to support the burnup extension goals and investi-gate high burnup fuel behaviors while establishing unique in-pile LOCA test capabilities.Project DescriptionTo support in-pile LOCA testing in TREAT, an experiment vehicle known as the Transient Water Irradiation System in TREAT (TWIST) is being developed. TWIST will be used as a consolidated water reactor testing system in the TREAT facility. The TWIST design is based on previous LOCA device concepts from recent years with the goal of better representing fuel condi-tions starting from normal operations fuel through the LOCA event. TWIST consists of a pressurized static water Figure 1. TWIST design rendering144 2021|AFC ACCOMPLISHMENTS'