  Under standard operating conditions, the emissivity of structural alloys used
for various components of nuclear reactors may evolve, affecting the heat
transfer of the systems. In this study, mid-infrared emissivities of several
reactor structural alloys were measured before and after exposure to
environments relevant to next-generation reactors. We evaluated nickel-based
alloys Haynes 230 and Inconel 617 exposed to helium gas at 1000 $^{\circ}$C,
nickel-based Hastelloy N and iron-based 316 stainless steel exposed to molten
salts at 750-850 $^{\circ}$C, 316 stainless steel exposed to liquid sodium at
650 $^{\circ}$C, and 316 stainless steel and Haynes 230 exposed to
supercritical CO2 at 650 $^{\circ}$C. Emissivity was measured via emissive and
reflective techniques using a Fourier transform infrared (FTIR) spectrometer.
Large increases in emissivity are observed for alloys exposed to oxidizing
environments, while only minor differences were observed in other exposure
conditions.
