Zircaloy-Clad Fuel Rod Burst Behavior under Simulated Loss-of-Coolant Condition in Pressurized Water Reactors

To study behaviors of zircaloy-clad fuel during loss-of-coolant accidents in PWR, simulated fuel rods having five pressure levels were heated in steam or vacuum at heating rates between 3 and 47°C/sec. The extent of ballooning of fuel rod is chiefly found within 30 mm from the center of rupture opening. The maximum diametral expansion is mainly related to the burst temperature, as it decreases between about 830°C and about 920°C. The maximum diametral expansions in vacuum are larger than those in steam. The average wall thickness varied with ballooning depends on heating method and atmosphere, and is represented to be about two-third of maximum diametral expansion. Oxide thickness on inner surface is apparently thicker than that on outer, when amount of supplied steam to inner surface is less. The porous thicker inner oxide consists of monoclinic and tetragonal zirconia, and higher hydrogen content is closely associated with the occurrence of tetragonal zirconia.