Emittance of Zircaloy-4 Sheath at High Temperatures in Argon and Stearn Atmospheres

Abstract

The spectral emittance of Zircaloy-4 sheath at wavelengths 1.0 and 2.3 vm was measured between 1100 and 1650 degrees C in an argon and steam atmosphere. The results showed that at a given temperature the emittance increases rapidly from an initial value of about 0.3 in argon to a value of about 0.8-0.9 during steam oxidation. This change in emittance is associated with the color change of the fuel sheath, from bright metal in argon to black oxide in steam. An increase in the surface temperature of the Zircaloy-4 sheath led to a small decrease in emittance. A linear correlation between emittance and sheath temperature was obtained. No significant change in emittance was observed at the tetragonal to cubic phase transition temperature of 1580 degrees C.