Identification and quantification of hydride phases in Zircaloy-4 cladding using synchrotron X-ray diffraction

• Published in: Journal of nuclear materials Vol. 392; no. 3; pp. 453 - 463
• Main Authors: Daum, R.S., Chu, Y.S., Motta, A.T.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-08-2009; Elsevier
• Subjects: Applied sciences; Controled nuclear fusion plants; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Fission nuclear power plants; Fuels; Installations for energy generation and conversion: thermal and electrical energy; Nuclear fuels; Corrosion; Zircaloy; Hydrogen; Synchrotrons; Zirconium hydride; Concentration effect; High temperature; Clad; X ray diffraction; Light water reactor; Nuclear reactor
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2009.04.004

Zirconium hydrides precipitate in fuel cladding alloys as a result of hydrogen uptake from the high-temperature corrosion environment of light water reactors. Synchrotron X-ray diffraction was performed at room temperature on stress-relieved Zircaloy-4 cladding with two distributions of hydrides – (1) uniformly distributed hydrides across the entire cladding wall and (2) hydride rim next to the outer surface. The δ-hydride phase was found to be the predominant hydride phase to precipitate for hydrogen contents up to 1250 weight parts per million (wt
ppm). At a higher content, about 3000
wt
ppm, although δ-hydride is still the majority phase, a significant amount of γ-hydride is also observed. At even higher hydrogen contents, in excess of approximately 6000
wt
ppm, such as can occur in a highly dense hydride layer, peaks associated with the ε-hydride phase are also observed in the diffraction pattern. The volume fraction of hydrides was estimated as a function of hydrogen content using the integrated intensities of select diffraction peaks corresponding to the α-Zr matrix and the hydride phases. These estimated values agree well with calculated values from the independently measured concentrations. The results of this study indicate that hydride precipitation in Zircaloy-4 is a complex process of evolving hydride phases with increasing local hydrogen content.