b'4.1 IN-REACTOR LOCA TESTING CAPABILITYIn-Reactor LOCA Testing CapabilityPrincipal Investigator: Nicolas Woolstenhulme Team Members/ Collaborators: Colby Jensen, Charlie Folsom, Klint Anderson, Leigh-Ann AstleTWIST will enableT he unexpected closure ofin TREAT. It was shown that this the Halden Boiling Watercapability would need to provide Reactor eliminated the onlyadequate heat transfer conditions unprecedented in- in-reactor Loss of Coolant Accidentfor a test rod during a brief part reactor experiment(LOCA) testing capability availableI power transient in TREAT in capabilities inin the western world. This capabilityorder to develop representative manipulating thermalwould have been key in continuedpre-LOCA thermomechanical hydraulic and nuclearresearch about Fuel Fragmentationgradients and stored energy in the heating conditionsRelocation and Dispersal (FFRD),test rod. Then, this device would to simulate LOCAespecially with ongoing efforts toneed to significantly reduce heat conditions. extend the allowable fuel burnuptransfer conditions and support a limits in Light Water Reactorlonger part II power transient to (LWR). Thankfully LOCA testingelevate rod cladding temperature programs, based on hot cell furnaceand create balloon, burst, and FFRD capabilities at Studsvik Sweden andbehaviors. After comparing options Oak Ridge National Lab, continuedincluding a flowing water loop, to investigate these behaviorsnatural circulation capsule, and alongside various efforts to modelstatic water capsule with nucleate LOCA fuel performance and under- boiling, it was found that the latter stand its effects. Still, the abilitywould provide the most practical to perform highly representativeapproach to supporting part I of the LOCA testing with nuclear heatingtransient. Then, TREATs automatic was known to be a major capabilitytransient control system would be gap. A few years of engineeringsynchronized with a remote actuated studies have investigated optionsvalve to allow fast water draining and ultimately produced the designto support part II of the transient. A for a new in-reactor LOCA capabilitysmaller version of this capsule was in the Transient Reactor Testconceptualized, but ultimately a facility (TREAT). The final designlarger version termed the Transient for this device has been completed,Water Irradiation System for TREAT out-of-reactor prototype testing is(TWIST) underwent final designunderway, and plans are in place toand engineering.perform in-reactor commissioningAn early prototype of the TWIST tests nest year. capsule was constructed and Project Description: demonstrated the functionality of A few design options were investi- the remote blowdown valve. As gated via modeling to determine theprototype often do, these efforts best path forward for LOCA testingrevealed a glitch with the assembly/142 2022|AFC ACCOMPLISHMENTS'