b'The FAST experiments will contain metallic fuel for sodium fast reactors (SFR) and will be inserted into the ATR during the 168B cycle (tentatively March 2020). The experiments will include up to fifty different fuel specimens that are designed to provide data for fuel performance model validation and irradiated material for postirradiation (PIE) testing (e.g., furnace testing for creep). The test matrix encompasses a large array of fuel concepts including: Control specimens for comparison to historical irradiations Fuel additives and liners for mitigating fuel-cladding chemical interactions (FCCI) at high burnup Variable smear densities for studying unrestrained fuel swelling Sodium free annular fuel for once-through fuel systems Varying fuel alloy specimens (U, U-Pu, and U-Pu-Zr) with liners to test increased heavy metal loading Very low burnup for evaluating early microstructure changes and com-paring accelerated irradiation effects Figure 1. Schematic of the FAST capsule design. a) The FAST-OA capsule with the single rodlet per capsule design. b) The FAST-SI capsule with the double rodlet per capsule design.2019|AFC ACCOMPLISHMENTS 197'