The speciation of niobium in the oxide layer of an irradiated Low-Tin ZIRLO nuclear material

J Hawes,P Warnicke,P Burr,D Ferreira Sanchez,D Grolimund,J Partezana,Y.-L Chiu,S Abolhassani

doi:10.1016/j.corsci.2021.109630

Abstract

In this study the oxidation state of niobium, within the oxide layer of a low-tin ZIRLO11ZIRLO is the trade name of a zirconium based alloy produced by Westinghouse Electric Company. irradiated in a nuclear reactor, is examined using synchrotron. The unique set up allows simultaneous acquisition of X-ray florescence (XRF) and X-ray diffraction (XRD) maps. A gradual oxidation and evolution of niobium is observed and quantified which is then compared with the information on the distribution of oxide phases revealed by XRD. The results are discussed with the aim to better understand the hydrogen uptake mechanism for this material, particularly the cause of the increased resistance to hydrogen uptake seen in niobium containing alloys.

Highlights

Zirconium alloys are used as nuclear materials because of their good corrosion resistance and low neutron capture cross section
The spectrum designated with 0 μm represents the metal-oxide interface, negative distances correspond to the metal and positive distances correspond to the oxide
The aim of this work has been to study the speciation of Nb in the oxide layer of a ZIRLO alloy, near the metal oxide interface, to verify two points: i) is there any Nb2O5 present in the oxide? And ii) what is the exact speciation of the Nb as the distance from the metal-oxide interface increases? The interest for this information stems from the observation that in the case of Nb containing Zr alloys, the speciation of Nb in fluences the charge compensation near the interface and reduces the hydrogen pickup fraction (HPUF) in these alloys [3,4,8,9]

Summary

Introduction

Zirconium alloys are used as nuclear materials because of their good corrosion resistance and low neutron capture cross section. Alloying elements have been added to improve corrosion performance and lower hydrogen uptake. Some of these alloying elements, in particular if they have a low solid solubility in zirconium, will form intermetallic or secondary phases particles (SPPs), and provide anodic protection for oxidation [1] since the alloying elements are more elec tronegative than Zr. It is crucial that a protective oxide is maintained to prevent breakaway (rapid) oxidation. It is crucial that a protective oxide is maintained to prevent breakaway (rapid) oxidation It has been observed in the past that some of these SPPs show a delayed oxidation in the oxide, and may contribute to the enhanced resistance to rapid corrosion [2]

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Results

Conclusion