b'TWIST LOCA Device Assembly and CommissioningPrincipal Investigator: Colby JensenTeam Members/Collaborators: Klint Anderson, Cindy Fife, Connor Michelich, Todd Birch, Ashley Lambson, Charles Folsom, Robert Armstong, Clint Wilson, Kelly Ellis, Changhu Xing, Nicolas WoolstenhulmeThe completedL oss of coolant accident (LOCA)heating, with achievable rod powers testing is critical to supportand temperatures prototypic of LOCA ongoing efforts to extend theevents. Figure 1 shows the TWIST assembly andallowable fuel burnup limits in lightexperiment assembly, including the commissioning of thewater reactors (LWRs). This testingcapsule and expansion tank.TWIST device providesalso allows continued research the U.S. with a LOCAon fuel fragmentation relocationThe TWIST capsule was designed to and HBu LWR transientand dispersal (FFRD). To addressbe the LWR testbed for TREAT experi-test device to performindustry needs, and to help elimi- ments with pre-irradiated fuel and is critical safety testing fornate capability gaps resulting fromplanned to be used for LOCA and reac-advancing LWR fuel. the closure of the Halden Boilingtivity-initiated accident (RIA) experi-Water Reactor (HBWR), a LOCAments on High-Burnup (HBu) fuel. testing device was developed for useThe TWIST capsule accommodates in the Transient Reactor Test Facilityrodlets with fueled lengths ranging (TREAT). The final design for thisfrom 25 to 50 cm and features a state-device has been completed, compo- of-the-art instrumentation package nents have been fabricated, the firstto collect relevant time-dependent experiment has been assembled, anddata for post-test analysis of the the commissioning of the device hasexperiment. The commissioning test commenced in TREAT. instrumentation package includes an electroimpedance sensor to detect Project Description: phase change events in the water The Transient Water Irradiationand cladding radial dimension, a System in TREAT (TWIST) providespyrometer, thermocouples to measure a controlled environment in whichcladding and surrounding environ-a blow-down event can be simulatedment temperatures, optical pressure by actuating a valve to release watersensors, and an acoustic emission from the upper capsule containingsensor to detect cladding rupture. a fuel specimen into an expansionThe design also includes options to tank below. The approach will fillmeasure either the fuel centerline the in-pile LOCA testing gap lefttemperature or rodlet pressure.by HBWR and adds capability toThe commissioning test series in study stored energy heating effectsTREAT will be executed with fresh resulting in temperature ramp ratefuel specimens to demonstrate and effects, never evaluated before onqualify the TWIST system in prepara-irradiated LWR fuels. These behaviorstion for HBu experiments, confirm are expected to play important rolespower coupling in all planned experi-in FFRD, the primary challenge toment configurations, and provide extending the regulatory burnup limitdetailed thermal hydraulic validation. beyond 62 GWd/t. The unique designTesting of pre-irradiated fuels in of the TWIST device allows highlyTWIST for the High burnup Experi-representative testing using nuclear 102 2023|AFC ACCOMPLISHMENTS'