Several power generation technologies have interest in employing a supercritical CO2 (sCO2) cycle but relatively little compatibility work has been conducted at the target pressure range of 200–300 bar, particularly at ≥700 °C. With the goal of utilizing lower pressure data sets (especially with controlled O2 and H2O contents), this initial assessment compared the effect of CO2 pressure at 1–300 bar on the compatibility of potential Fe‐ and Ni‐base structural alloys after 500 h exposures at 750 °C. For highly‐alloyed alumina‐ and chromia‐forming alloys, a minimal effect of pressure was observed on the mass change and reaction products, which were similar to those observed in 1 bar dry air, CO2, CO2–0.15%O2 and CO2–10%H2O. After these relatively short exposures, there was no obvious indication of internal carburization and the Cr depletion in the precipitation strengthened Ni‐base alloys (740 and 282) was minimal. In addition to coupons, 25 mm long tensile specimens of alloy 740, 247, 310HCbN, and E‐Brite (Fe–Cr) were exposed in each condition but did not show any detrimental effect of the high‐purity CO2 environments on room temperature tensile properties.

a b s t r a c tA CALPHAD assessment of the U-Y-O system has been developed. To represent the YO 2 compound in the compound energy formalism (CEF) for U 1Ày Y y O 2±x , the lattice stability was calculated using density functional theory (DFT) while a partially ionic liquid sub-lattice model is used to describe the liquid phase. A Gibbs function for the stoichiometric rhombohedral UY 6 O 12 phase is proposed. Models representing the phases in the U-O and Y-O systems taken from the literature along with the phases that appear in the U-Y-O ternary are combined to form a complete assessment.

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