In-service inspections of Zr-2.5Nb pressure tubesmay reveal blunt flaws such as fretting wear or crevicecorrosion marks. These flaws pose no immediate threatto the integrity of the pressure tube. However, such flawsare potential fatigue initiation sites. If a fatigue crackinitiates, a blunt flaw could then behave like a planar flawdue to the potential for hydride cracking. Anunderstanding of the effect of the reactor coolantenvironment, specifically on fatigue crack initiation, isimportant in this context. Corrosion fatigue crackinitiation tests data were conducted on notched transversetensile specimens at 300 °C, with a maximum load ofapproximately 750 N and the ratio of the minimum tomaximum load ? of 0.2. The tests investigated theeffects of applied loading frequency, the effect of hydridesand the effect of a hold time on crack initiation in both anair and water environment. Following fatigue testing,samples were characterized using transmission electronmicroscopy (TEM) and electron energy loss spectroscopy(EELS) to elucidate the microscopic mechanisms forfatigue crack initiation at the crack tip. The plastic zonesize surrounding the notch was also determined usingnanoindentation.
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