Abstract
Zr-Sn-Nb-Fe alloys are one of the important directions for continuous improvement of zirconium alloys for high burn-up fuel assemblies. The corrosion resistance of Zr-Sn-Nb-Fe alloys is closely related to the alloying element and water chemical condition. To better understand the effect of Sn on corrosion resistance of Zr-Sn-Nb-Fe alloy, the normal N36 (Zr-1Sn-1Nb-0.3Fe) and low-tin N36 (Zr-0.8Sn-1Nb-0.3Fe) alloy sheets were prepared and tested in static autoclave in both of 0.01 mol/L LiOH and 0.03 mol/L LiOH aqueous solution at 360°C and 18.6 MPa. The characteristics of the microstructure and oxide film of alloys were analyzed by TEM and SEM respectively. It was shown that that the corrosion transition of the normal N36 appears earlier and the weight gain is higher than the low-tin N36 in two corrosive mediums. The cracks paralleling to the interface of oxide/metal are formed in the fracture surface of the oxide film and the micrographs at the oxide film/substrate interface appear uneven morphology. With the increasing of corrosion gain, there are more parallel cracks in oxide film and the uneven morphology at the oxide film/substrate interface is more obvious.
Highlights
Zirconium alloys are extensively used to manufacture nuclear reactor components such as fuel claddings, coolant channels, pressure tubes and other in-core structural components due to a low neutron absorption cross section, superior corrosion resistance and high mechanical strength etc
The cracks paralleling to the interface of oxide/metal are formed in the fracture surface of the oxide film and the micrographs at the oxide film/substrate interface appear uneven morphology
With optimizing research [4] [5] about ZIRLO and E635 alloys, it showed the corrosion resistance can greatly increases by reducing Sn content in Zr-Sn-Nb-Fe alloys, but too little Sn will lead to accelerated corrosion of alloys in LiOH aqueous solution, which how to accelerate Zr-Sn-Nb-Fe alloys corrosion is still obscure at present [6] [7] [8]
Summary
Zirconium alloys are extensively used to manufacture nuclear reactor components such as fuel claddings, coolant channels, pressure tubes and other in-core structural components due to a low neutron absorption cross section, superior corrosion resistance and high mechanical strength etc. Many countries have been developing new zirconium alloys cladding materials by optimizing Zr-Nb and Zr-Sn series alloys and obtained many Zr-Sn-Nb series new zirconium alloys, such as ZIRLO, E635 and X5A [1] [2] [3], and their corrosion resistance in LiOH aqueous solution are obviously better than Zircaloy-4. The effect and mechanism of Sn content on corrosion resistance of N36 zirconium alloy in LiOH aqueous solution were discussed
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