A review of factors influencing the hydride reorientation phenomena in zirconium alloy cladding during long-term dry storage

Abstract

Zirconium-based alloys, widely used for nuclear fuel cladding, are highly susceptible to hydrideinduced embrittlement. The degree of the hydride embrittlement is strongly affected by not only its concentration but also its morphology. The hydride can drastically reduce the mechanical properties of the cladding, especially when it is radially precipitated. Recently it has been reported that circumferential hydrides can re-precipitate into radial hydrides if applied hoop stress in the cladding exceeds a certain limit, so-called threshold stress, during the long-term dry storage of spent nuclear fuel. This hydride reorientation phenomenon is now considered as one of the most critical issues in the nuclear fuel industry, threatening cladding integrity during the steady state storage period as well as transportation of spent nuclear fuel. In fact, the phenomenon is known to be quite complex, and affected by numerous factors. In this paper, the major influential factors affecting reorientation issues, namely temperature, stress, number of thermal cycles, cooling rate, and hydrogen concentration, are reviewed. In addition, recent studies on the synergistic effects of the factors on the threshold stress triggering the reorientation are discussed in detail. Finally, summarizing conclusions for mechanistic understanding are drawn and recommendations for future work are made.