Study on Stress in Oxide Formed on Cladding of Fuel Rod from Qinshan Phase Ⅰ NPP

Zirconium alloys are often used as nuclear fuel cladding in pressurized water reactors. Oxidation of these alloys is a limiting factor in the lifetime of the fuel. To extend the burn-up of the nuclear fuel requires the control of the corrosion, it is necessary to study the cladding corrosion process. The composition and the residual stress of the oxide films of the spent fuel rod from Qinshan Power Plant Phase Ⅰ were investigated by XRD method and stress measurement instrument. The results indicate that the compressive stress exists in the oxide film, and the value decreases gradually from the bottom to the top of the fuel rod. However, the stress at the air chamber suddenly increases after it gradually stabilizes at the minim value. Also, the stress has very important effect on the stability of the t-ZrO₂, and the composition of the film gradually transforms to the monoclinic phase along with the releasing of the stress caused by the development of cracks.