b'Figure 2. Comparison of 1 % offset effective shear stress and maximum effective shear stress at doses between 15 and 20 dpa for a) HT-9 and b) 14YWT as a function of irradiation temperature. Dotted lines mark the average max and 1 % offset shear strain for the unirradiated control samples tested at room temperature.induced hardening and iv) evalu- hundreds of dpa and temperatures of ating mechanical testing techniques400-600 C, which is significantlyEvolution of mechanical for small material volumes. higher than the requirements forbehaviors of structural All of these technical objectivescurrent generation light watermaterials at high directly support the developmentreactors (LWRs). Doses expectedneutron irradiation of safe, reliable and economic nextin SFR at lower temperatures (e.g.,doses is complex, generation reactors, particularly350-400 C) are lower but strongand understanding sodium cooled fast reactors. Thehardening is observed at thoseit is critical to the ferritic steels investigated are relevanttemperatures. Thus, data is needed tosafe implementation fuel cladding and in-core structuralcharacterize mechanical propertiesof advanced reactor materials, based on the prior perfor- after low temperature irradiationdesigns.mance of traditional HT-9 in thealso. Understanding the effect of experimental breeder (EBR)-II fastboth irradiation dose and irradiation reactor and the promise of bettertemperature on the evolution of irradiation tolerance of advancedmechanical properties of structural ferritic alloys including ODS 14YWT.materials is critical to ensure the safe and reliable operation of next Cladding materials for Generationgeneration nuclear reactors.IV fast reactors, such as the sodium fast reactor (SFR), will be subjected to irradiation damage levels in the 2019|AFC ACCOMPLISHMENTS 179'