Experimental study and numerical simulation of high temperature (1100–1250 °C) oxidation of prior-oxidized zirconium alloy

Abstract

Previous experiments showed that the thickness of a thick prior-oxide layer formed on Zircaloy-4 fuel cladding can decrease during the first seconds at very high-temperature, before re-growing. We confirmed these results with oxidations performed at 1200 • C on prior-oxidized Zircaloy-4. The initial reduction of the prior-oxide was explained by the balance of the oxygen fluxes at the metal/oxide interface and successfully reproduced by numerical simulations using a diffusion-reaction model. Different hypotheses were considered for the diffusion coefficients of oxygen in the different layers. This allowed discussing the effect of the prior-oxidation on the kinetics of oxygen embrittlement of the metallic substrate. Abbreviations: ␣ red , ␣Zr(O) phase formed by reduction of the low temperature oxide layer; Exp, experimental, i.e. data link with experimental results; EKINOX-Zr, Estimation KINetics OXidation numerical model for Zr alloys; HCP, hexagonal close-packed; HT, high temperature; HTox/HT ZrO2, oxide layer formed at high temperature (T ≥ 1000 • C); LOCA, loss-of-coolant-accident; LT, Low temperature, i.e. the in-service temperature of the PWR (T≈320 • C); LTox/LT ZrO2, oxide layer formed at low temperature; Num., numerical, i.e. data link to numerical results; PBR, Pilling-Bedworth ratio; Prior-␤Zr, phase formed from the cooling of ␤Zr phase stable at high temperature; PWR, pressurized-light-water-reactor.

Experimental study of oxidation in oxygen, nitrogen and steam mixtures at 850∘C of pre-oxidized Zircaloy-4

“…The effect of a very thin preoxide layer (≈1 µm) on subsequent high temperature steam oxidation of Zy-4 was studied by Kawasaki et al [13]. More recently, the effect of a pre-oxide scale on subsequent HT oxidation of zirconium alloys was investigated on Zy-4 cladding materials, under steam [14][15][16][17] or under oxygennitrogen atmospheres [18]. Results of air oxidation in the 850-1000°C temperature range of preoxidized cladding tubes [18] indicate that a pre-oxide layer of approximately 30 µm acts, for a limited time period (a few hours at maximum), as a protective layer against further HT oxidation.…”

Volatile corrosion inhibitors for ferrous and non-ferrous metals and alloys: A review

“…In the flowing case, metallic corrosion would be more severe because moving electrolyte molecules continuously remove the rusts and scales accumulated on the surface leading to exposure of new metallic surface for corrosion as compared to the static conditions. Under static conditions, the nature of corrosion products can be estimated by Pilling-Bedworth ratio which is presented by Md/nmD [31,32]. In this formula, m and M represent atomic mass and molecular mass of metal under consideration and corrosion products (rusts), respectively, d and D denote the densities of metal under taken and corrosion products, respectively and n signifies number of metallic atom in the formula of corrosion product.…”

Dendrimers as novel class of polymeric corrosion inhibitors: A review

“…Besides these environmental factors, corrosion rate is also influenced by nature of rusts and scales accumulated on the metallic surface which may or may not be protective. The inhibitive and corrosive nature of the accumulated rusts and scales collected on the metallic surface can be determined by Pilling-Bedworth ratio which is generally expressed by Md/mnD [12,13]. In the Pilling-Bedworth ratio M and D are respectively, represent the molecular weight and density of the rusts and/or scales gathered on the surface.…”

“…In the Pilling-Bedworth ratio M and D are respectively, represent the molecular weight and density of the rusts and/or scales gathered on the surface. Whereas, m and d, respectively represent the atomic weight and density of the metal under consideration and n represents the metallic number in the rusts and scales (corrosion products); for example in Fe 2 O 3 , Al 2 O 3 and Fe 3 O 4 , n are 2, 2 and 3 respectively [12,13]. In general, for case Md/mnD < 1, it is expected that volume of metal surface is larger than that of the corrosion products (rusts/scales) and therefore surface film is non-protective as it contains exposed metallic area.…”