b'FM steels such as HT-9 have been Understandingused historically for fast reactor mechanical propertiesfuel cladding and in-core structural of structural materialsmaterials including in the Experi-after high irradiationmental Breeder Reactor (EBR-II) dose is necessary forfast reactor and the Fast Flux Test designing advancedFacility (FFTF). HT-9 steel, is a reactors.Fe-12Cr steel with additions of Mo, Mn, Ni, V and W. With a BCC crystal structure and a high density of sinks for defects including dislocations, fuels require cladding materialsmartensitic lath boundaries, and that can withstand high irradiationprecipitates, HT-9 has a low steady doses, at intermediate to elevatedstate swelling rate and long incuba-temperatures and in corrosivetion period. HT-9 also has excellent environments. Cladding materialscorrosion resistance in sodium. for Generation IV fast reactors, suchModern NFAs including the oxide as the sodium fast reactor, will bedispersion strengthened (ODS) steel, subjected to irradiation damage14YWT, improve upon the tradi-levels in the hundreds of dpa andtional ferritic/martensitic (F/M) temperatures of 400-600 C, whichsteels with better high temperature is significantly higher than themechanical properties and swelling requirements for current generationresistance. The uniform dispersion light water reactors. Lower doses areof nano-scale oxide particles act as expected in sodium fast reactors atbarriers to dislocations as well as lower temperature (e.g., 350-400recombination sites for irradiation C) regions, but strong hardeninginduced vacancies and interstitials. is observed at these temperatures.This project provides mechanical Thus low temperature irradiationtesting on high dose neutron irradi-data is important to characterizeated materials, comparing traditional mechanical properties.materials such as HT-9 to advanced alloys including 14YWT.2020|AFC ACCOMPLISHMENTS 143'