SEDL / STP / STP681-EB / STP36671S

Effect of Material and Environmental Variables on Localized Corrosion of Zirconium Alloys

Lunde, L
Metallurgist and head of metallurgy division, Institutt for atomenergi, Kjeller,

Videm, K
Metallurgist and head of metallurgy division, Institutt for atomenergi, Kjeller,

Pages: 20    Published: Jan 1979

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Abstract

The nodular attack of α-annealed Zircaloy-2 and Zircaloy-4 in steam at 500°C is dependent upon the presence of hydrogen in the environment, the important function being the hydrogen to steam ratio rather than partial pressures. The uniform corrosion between the nodules was unaffected by the hydrogen in the steam. β-quenched Zircaloy-2 showed the opposite behavior, suffering nodular corrosion in hydrogen-free steam and corroding uniformly in steam with hydrogen additions. Nodules did initiate on Ozhenite-0.5, but did not develop into serious localized attack for α-annealed material. Alloys with higher niobium content and Valoy were independent of hydrogen in the steam and they never suffered localized corrosion. The chromium-rich particles in Valoy did not influence the oxidation of the matrix adjacent to the particles under hydrogenated conditions. The iron-rich particles in the Zircaloys and in Ozhenite-0.5 decreased the oxidation of matrix in a region around each particle. Nodules initiated by oxide cracking over grain boundaries in areas with few intermetallic particles. The observed influence of hydrogen in the steam on nodular corrosion is attributed to its effect on the electron conductance of the oxidized iron-rich precipitates.