Material Selection for Accident Tolerant Fuel Cladding

Alternative cladding materials to Zr-based alloys are being investigated for accident tolerance, which can be defined as > 100X improvement (compared to Zr-based alloys) in oxidation resistance to steam or steam-H-2 environments at >= 1473 K (1200 degrees C) for short times. After reviewing a wide range of candidates, current steam oxidation testing is being conducted on Mo, MAX phases, and FeCrAl alloys. Recently reported low-mass losses for Mo in steam at 1073 K (800 degrees C) could not be reproduced. Both FeCrAl and MAX phase Ti2AlC form a protective alumina scale in steam. However, commercial Ti2AlC that was not single phase, formed a much thicker oxide at 1473 K (1200 degrees C) in steam and significant TiO2, and therefore, Ti2AlC may be challenging to form as a cladding or a coating. Alloy development for FeCrAl is seeking to maintain its steam oxidation resistance to 1748 K (1475 degrees C), while reducing its Cr content to minimize susceptibility to irradiation-assisted alpha' formation. The composition effects and critical limits to retaining protective scale formation at > 1673 K (1400 degrees C) are still being evaluated. (C) ASM International (ASM) and The Minerals, Metals & Materials Society (TMS) 2015