Comparison of High-Temperature Steam Oxidation Kinetics Under LWR Accident Conditions: Zircaloy-4 Versus Austenitic Stainless Steel No. 1.4970

Abstract

A comparative study of the oxidation behavior of Zircaloy-4 versus austenitic stainless steel No. 1.4970 was performed in high-temperature steam. Nuclear reactor-type tube sections of both materials were exposed on both sides to superheated steam at temperatures ranging from 600 to 1300°C for up to 6 h. The specimens were evaluated by gravimetry, metallography, and other methods. The results are presented in terms of weight gain, corresponding metal consumption, and wall penetration as functions of time and temperature. The two materials behaved similarly in that the faster oxidation of the thicker Zircaloy-4 cladding consumed the total wall thickness in a time equivalent to the slower oxidation of the thinner stainless steel cladding. Besides oxide scale formation, oxygen diffusion into the bulk of the metal formed various oxygen-containing phases, which together influence the mechanical cladding properties. Remarkable swelling of tube dimensions was caused by oxidation.

Steam oxidation of boron carbide–stainless steel liquid mixtures

“…However, a Cr 2 O 3 protective coating is observed at the surface of the metal oxidised in air. The parabolic constant obtained in our study is intermediate between those obtained by Bittel in air (0.0074 mg An inner protective layer of iron-ni ckel-chromium spinel was also developed in stainless steels with Cr and Ni contents (15% Cr, 15% Ni and 18% Cr, 8% Ni) close to that of the 304 L stainless steel and exposed to steam oxidation at temperatures up to 1289°C[22][23]. The layers formed above the steel melt after oxidation coincide with those observed by Rao and Robertson[24] after oxidation of pure Fe-18%Cr-0.1%C levitated drops with oxygen at 1600-1700°C.…”

The oxidation behavior of Zircaloy‐4 in steam between 600 and 1600°C

“…As consequences of hydrogen saturation, as described above, and the total consumption at 1000 "C [21], the linear parts of the kinetic curves are short. Continued linear behavior undisturbed by limited matter could be expected only for thicker tubes or massive bar or sheet specimens.…”