Alloys of iron-chromium-nickel are being explored as alternative cladding materials to improve safety margins under severe accident conditions. Here, our research focuses on non-destructively investigating the oxidation behavior of the FeCrNi alloy ?Alloy 33? using synchrotron-based methods. The evolution and structure of oxide layer formed in steam environments were characterized using X-ray diffraction, hard X-ray photoelectron spectroscopy, X-ray fluorescence methods and scanning electron microscopy. In conclusion, our results demonstrate that a compact and continuous oxide scale was formed consisting of two layers, chromium oxide and spinel phase (FeCr<
sub>
2<
/sub>
O<
sub>
4<
/sub>
) oxides, wherein the concentration of the FeCr<
sub>
2<
/sub>
O<
sub>
4<
/sub>
phase decreased from the surface to the bulk-oxide interface.