2017 | AFC ACCOMPLISHMENTS 96 Combined Experiment and Modeling for Beyond Design Basis Accident Analysis Principal Investigator: Kevin Robb Collaborators: Bruce Pint, Kurt Terrani, Larry Ott To guide the development and prioritization of Accident Tolerant Fuel (ATF) concepts, there is a need to assess their performance under accident condi- tions.To perform these assessments, experimental data such as oxidation kinetics and material failure points are required. Iron-chromium- aluminum (FeCrAl) alloys are under active development to serve as core materials with enhanced accident tolerance.To accelerate development and deployment, concurrent efforts have been underway to optimize the alloy, generate the required test data, and conduct assessments of the ATF concept performance. Project Description The first-generation alloy, B136Y (Fe-13Cr-6Al), developed at Oak Ridge National Laboratory (ORNL) has more favorable irradiation prop- erties than that of the commercially available APMT alloy. However, unlike the APMT alloy, the oxidation kinetics for B136Y have not been developed. The B136Y alloy will be used in an upcoming QUENCH test at the Karl- sruhe Institute of Technology (KIT). The QUENCH test will provide inte- gral test data as to the performance of the alloy under conditions it could experience during an accident.The oxidation kinetics of B136Y need to be developed to: 1) inform and interpret the QUENCH test, and 2) provide more accurate material prop- erties for use in modeling accidents during concept assessments. Accomplishments Sections of B136Y FeCrAl tubing were exposed to a steam environ- ment in the Severe Accident Test Station (SATS) High Temperature Furnace at ORNL (Figures 1 and 2). The furnace temperature was varied during two series of tests to simu- late: 1) the anticipated conditions during the upcoming QUENCH test; and 2) the predicted prototypic conditions based on previous station blackout simulations.Through 15 tests, the oxidation kinetics rate constant for B136Y was found to be 3-5 times higher than that of the commercial APMT alloy.The tests have also provided confidence that the cladding will retain a coolable geometry up to 1500°C under temperature ramp rates characteristic of station blackout scenarios. The MELCOR code was used at ORNL to perform integral simulations of Boiling Water Reactor (BWR) beyond design basis accidents. Based on the oxidation test results, the oxidation rate constant was varied from 1x-10x that of AMPT (Figures 3 and 4). Since the oxidation rate of FeCrAl is so low compared to zirconium based alloys, increasing the FeCrAl oxidation rate constant over this range was found to have only secondary or tertiary impacts on the predicted accident progression.The predicted gains afforded by the FeCrAl ATF concept were found to be consistent with previous year’s work. Concurrent high- temperature testing and accident modeling are informing FeCrAl ATF assessment.