b'4.2 TREAT LOCA TESTINGTREAT LOCA Testing and Large Experiment CapabilityPrincipal Investigators: Colby JensenTeam Members/Collaborators: Todd Pavey, Cindy Fife, Klint Anderson, Nicolas Woolstenhulme, and Colby JensenIdaho NationalT he Halden Boiling WaterA modified TWIST capsule has Reactor (HBWR) in Norwayalso been developed to support was a key resource forReactivity Initiated Accident (RIA) Laboratory establishesassessing nuclear fuels and materialstesting of longer length fuel rods capability to conductbehavior to address performancethan currently possible in the Static LOCA testing in TREATissues and answer regulatory ques- Environment Rodlet Transient Test recovering the gap losttions. When HBWR was shutdownApparatus (SERTTA) capsule. The by shutdown of thein 2018 the capability to conductTWIST capsule is equipped with Halden Boiling WaterLoss of Coolant Accidents (LOCA) instate-of-the-art instrumentation Reactor in Norway. a test reactor was lost. The Advancedto collect relevant data for post-Fuels Campaign has developed thetest analysis. The TWIST capsule Transient Water Irradiation Systemcompleted the first commissioning in TREAT (TWIST) experimenttest at the end of FY23 with three capsule to restore the LOCA testingadditional experiments to follow in for the industry. To commission theFY24. This is a critical step towards TWIST capsule in the Transientconducting LOCA experiments Reactor Test Facility (TREAT), theto investigate fuel fragmentation, reactor was modified for largerelocation, and dispersal for high experiment capability to allow inser- burnup light water reactor fuels.tion of the Big-Broad Use SpecimenTo support TWIST capsule and Transient Experiment Rig (Big- future experiments a large experi-BUSTER) in the center of the reactorment capability was established core. While TWIST commissioningin TREAT after several years of will be the first use of Big-BUSTER,planning and design. The large it is planned for use by all experi- experiment capability included ments for the foreseeable future,a new retro fit shield plug, new with backward compatibility withmoderator assemblies to convert existing capsules, making a notablethe core from four-inch by eight-shift in experimental approaches ininch experiment opening to a TREAT to loop-scale testing. ten-inch diameter experiment Project Description: opening, replacing BUSTER with The TWIST capsule provides a staticBig-BUSTER and a newly design water environment surrounding theand fabricated neutronic equivalent fuel rod with the ability to rapidlydevice (NED). The larger experi-drain the water from the capsulements allow for more room in the into a flask via an electronic blow- experiment capsules to enhance down valve during the transientthe experiments with new state-of-to simulate a LOCA on a fuel rod.the-art instrumentation and allow 200 2023|AFC ACCOMPLISHMENTS'