Deuterium permeation behavior in a FeCrAl-based alloy containing Mo, Nb and Ta elements for LWR cladding application

Abstract

The deuterium permeation behavior of a FeCrAl-based alloy containing Mo, Nb and Ta elements was investigated by gas-phase deuterium permeation testing, transmission electron microscopy, X-ray diffraction and electron backscatter diffraction methods. The results show that the higher the test temperature, the greater the steady-state permeation flux of the FeCrAl-based alloy. As the upstream deuterium pressure increases, the steady-state permeation flux of the FeCrAl-based alloy also increases. The pressure exponent n is between 0.5 and 1, indicating that deuterium permeation in the FeCrAl-based alloy is controlled by a combination of bulk diffusion and surface processes. This phenomenon is caused by the oxide film generated on the surface of the FeCrAl-based alloy during deuterium permeation test. The deuterium permeability of the FeCrAl-based alloy is about 37 times that of 316 L and 95 times that of Zircaloy-4 at the typical operating temperature of 300 °C. At 360 °C, the deuterium permeability of the FeCrAl-based alloy is about 25 times that of 316 L, and about 32 times that of Zircaloy-4. Compared with 316 L and Zircaloy-4 alloy, the activation energy of deuterium permeation of the FeCrAl-based alloy is smaller, indicating that deuterium permeates more easily in the FeCrAl-based alloy. The activation energy of deuterium diffusion in the FeCrAl-based alloy is also smaller, indicating that deuterium diffuses more easily in the FeCrAl-based alloy.