b'beginning with Cycle 164A onJune 12, 2018, and concluding with Cycle 169A on April 23, 2021. The first two cycles were irradiated with lower coolant temperatures (~250C) and pressures (13.5 MPa) on the lower end of prototypic PWR operating conditions. These were increased to their present values of 285C and 15.5 MPa in cycle 166A in July of 2019. At the start of Cycle 166B irradiation (November 2019), 7 of the baseline Zr alloy pins and 3 of the coated Zr alloy pins were removed. These were replaced with boiling water reactor (BWR)- sized pins. Prior to the start ofLinear heat rates for the test variedFigure 1. In-Core portion of the ATF-2 Cycle 168A in April of 2020, anotherfrom 200 W/cm to 450 W/cm. Peaktest trainminor reconfiguration was made toburnups reached were 30 GWd/MTU remove two additional baseline Zrand peak fast fluences in the cladding alloy pins and three Cr-coated Zr alloywere 4.9e25 n/cm 2 . Test pin examina-test pins. After Cycle 169A in April oftion data has been sent to all three 2021, three baseline Zr alloy pins, 13U.S. fuel vendors and is being used in coated Zr alloy pins, and 12 BWR-sizedthe development of their ATF prod-FeCrAl pins all were removed fromucts including licensing activities.the ATF-2 test train. Following theirMany ATF developers have begun removal, the test pins were shipped toto rely more heavily on lead test INLs Hot Fuels Examination Facilityassembly (LTA) irradiations in (HFEF), where they were subjectedcommercial reactors of their coated to nondestructive and destructiveZircaloy ATF technology. Thus, examination to determine how theythe goals of the ATF-2 missionFigure 2. Irradiated ATF-2 test pins performed in-pile. are evolving again to: (1) provideprior to destructive PIEPower histories, neutron fluxes, andcontinued irradiation of the small test pin depletions were calculatednumber of pins from the initial irra-for each cycle using a coupleddiation that require continued irra-MCNP and ORIGEN methodology.diation to high burnup; (2) support An MCNP Type 7 fission-energythe irradiation of more novel ATF (F7) tally is used to calculate antechnologies, such as silicon carbide energy deposition value in terms ofcomposite (SiC-SiC) cladding; and MeV/g per source neutron. MCNP(3) provide test space for the condi-Type 4 flux (F4) tallies are used totioning of refabricated pins from calculate the total flux, thermal fluxcommercial reactor irradiations prior (0.625 eV), and fast flux (1 MeV).to transient testing in INLs Transient The MCNP-calculated heat rates areReactor Test Facility (TREAT).fed into an ORIGEN input file and depleted over a given time interval. 2022|AFC ACCOMPLISHMENTS 21'