Oxidation kinetics of nuclear-grade FeCrAl alloys in steam in the temperature range 600-1500°C

Thin FeCrAl tubes are promising candidates for ATF cladding application. In this study, the high-temperature oxidation in steam of two nuclear-grade FeCrAl alloys developed by ORNL (B136Y3 and C26M2) was investigated over a wide temperature range. Transient oxidation tests from 500°C to 1250°C were conducted as well as isothermal experiments from 600°C to 1500°C. The well-accepted and in severe accident codes applied low oxidation kinetics determined by the formation of a protective α-alumina scale was confirmed only for the temperature range 1000-1250°C. At lower temperatures, the oxidation kinetics of both alloys followed rather the kinetics of transient alumina such as θ-alumina. At temperatures from approx. 1350°C, protective alumina formation failed resulting in much faster oxidation kinetics determined by the formation of iron oxides. This faster oxidation at low and high temperatures should be taken into account in codes for simulation of accident scenarios. Special effects of small open tube segments allowing oxidation of the inner surfaces and of thin wall thickness are discussed.