SEDL / STP / STP1245-EB / STP15213S

On the Initial Corrosion Mechanism of Zirconium Alloy: Interaction of Oxygen and Water with Zircaloy at Room Temperature and 450°C Evaluated by X-Ray Absorption Spectroscopy and Photoelectron Spectroscopy

Döbler, U
Sietec GmbH, Research Laboratory at BESSY, Berlin,

Knop, A
Sietec GmbH, Research Laboratory at BESSY, Berlin,
Institut für Festkörperphysik, Berlin,

Ruhmann, H
Siemens AG, Power Generation Group (KWU), Erlangen,

Beie, H-J
Siemens AG, Corporate Research and Development, Erlangen,

Pages: 19    Published: Jan 1994

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Abstract

The initial stages of zirconium oxide formation on Zircaloy after water (H²O) and oxygen (O²) exposures have been investigated in situ using photoelectron spectroscopy and X-ray-absorption spectroscopy. The reactivity of the zirconium alloy with O² at room temperature is about 1000 times higher than for H²O. Up to 100 L (1 L = 1 Langmuir unit = 1 ∙ 10^-6 mbar ∙ s) H²O exposure, the reactivity of the zirconium alloy at 450°C is comparable to the room temperature reaction. At higher H²O exposure, a sharp increase in the reaction rate for the high-temperature oxidation is observed. From the energy position of the Zr 3d photo emission line and their oxygen-induced chemical shifts, one can directly follow the formation of the oxide films. Two different substoichiometric oxides were found during reaction with water. Suboxide (1) is located at the zirconium/zirconium-oxide interface. Subsequently, a Suboxide (2) is concluded from the chemical shift of the zirconium photoelectrons. After an oxide thickness of 2 nm, the stoichiometric ZrO² phase is not yet developed.