A study was made of the oxidation kinetics and the identification of oxygen diffusion coefficients of low-Sn Zy-4 alloy at 973 to 1123K and at above 1373K. Two different cases were considered: dissolution of a pre-existing oxide layer at 973 to 1123K, and oxidation at >1373K. The oxygen diffusion coefficient in the αZr phase could be expressed as:

973 to 1123K:    D(cm2/s) = 6.798 x 100exp[-217.99(kJ/mol)/RT]

At 1373 to 1523K, the oxygen diffusion coefficients in αZr and βZr were determined by using the so-called inverse identification method. They could be expressed as:

Dα (cm2/s) = 1.543 x 100exp[-201.55(kJ/mol)/RT]

Dβ (cm2/s) = 6.8 x 10-3exp[-102.62(kJ/mol)/RT)

Finally the oxygen diffusion coefficient in αZr at 973 to 1523K was determined, by combining all of the results, to be:

Dα (cm2/s) = 4.604 x 100exp[-214.44(kJ/mol)/RT]

In order to check the calculated diffusion coefficients, oxygen concentration profiles were determined via electron probe micro-analysis in pre-oxidized low-tin Zy4 alloys annealed under vacuum at 973, 1073 and 1123K for different times, and compared to the calculated profiles. At last, within the framework of this study, it also appeared to be necessary to re-assess the Zr–O binary phase diagram in order to take into account the existence of a composition range in the two zirconia phases, αZrO2 and βZrO2.

Oxidation Kinetics and Oxygen Diffusion in Low-Tin Zircaloy-4 up to 1523K. X.Ma, C.Toffolon-Masclet, T.Guilbert, D.Hamon, J.C.Brachet: Journal of Nuclear Materials, 2008, 377[2], 359-69