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The microstructure of tungsten inert gas (TIG)-arc welding and resistance welding in Zircaloy 4 tubing is described in relation to the phases present. Differences in microstructure between the weld zone and base tubing are discussed in terms of the phase transformations that take place during the very different thermal cycles occurring in both processes and a comparison between them is made. A feature of the weld region is the presence of a coarse grained Widmanstatten structure in the TIG welding while a martensitic-type structure or very fine Widmanstt~tten structure is present in resistance welding.

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The water chemistry of the secondary coolant in the majority of Nuclear Power Plants is controlled by AVT (All Volatile Treatment), wherein volatile amines are used to maintain the alkaline pH required for minimizing the corrosion of structural materials which one of them is Carbon Steel. In this treatment, ammonia, morpholine and ethanolamine are commonly used as conditioning reagents. In this context, experiments were carried out by exposing carbon steel A106 B samples in a simulated secondary coolant in order to study the nature of the oxide films. The tests were performed in a static autoclave at 260˚C using two media: I) hydrazine + morpholine and II) hydrazine + ethanolamine during different exposure periods up to ≈1020 h. The oxide film characterization was mainly studied using Scanning Electron Microscopy and X-ray diffraction. A chemical descaling procedure was used to obtain the material weight loss (W) of samples, the adherent and released oxide. The XRD analyses, for all exposures studied, showed that magnetite was the corrosion product formed in the films grown in both media. The material weight loss, after descaling, could be fitted by a law of the type W = kt n , up to 1020 h of exposure tested, resulting in n = 0.42, k = 6.24 for films grown in medium I) and n = 0.39, k = 6.08 for films grown in medium II) respectively (W is in mg/dm 2 and t in h). The higher corrosion product release measured in the medium with morpholine could be important in power plant operation.