Hemispherical Total Emissivity of Potential Structural Materials for Very High Temperature Reactor Systems: Haynes 230

The hemispherical total emissivity of Haynes 230, which is regarded as a leading candidate material for heat exchangers in very high temperature reactor (VHTR) systems, was measured with various surface conditions using the ASTM C 835-06 protocol. The emissivity increased from 0.18 at 627 K to 0.235 at 1356 K for Haynes 230 as received sample. The emissivity increased significantly when its surface roughness was increased, or it was oxidized in air, or it was coated with graphite dust, as compared to the as-received material. Higher emissivity has a positive impact on high-temperature reactor operations, particularly for safety, since higher emissivity implies faster decay heat removal in postaccident VHTR environments.