Effect of water-steam boundary oscillations on the structural integrity of once-through steam generator tube

Once-through helical type steam generator is widely used for integral type reactor due to its compactness. Primary coolant flows outside of the tube and secondary coolant flows inside of the tube for most of once-through steam generators. The random oscillatory phenomena of the steam and water boundary conditions in the transition boiling zone have been observed in once-through steam generator tubes. Movement of the boiling boundary results in the oscillations of tube wall temperature. This oscillation cause thermal stresses which may cause the fatigue failure of the tube. Characteristics of the oscillations are mainly influenced by the heat transfer coefficient, flow rate, and other design parameters. Effect of this oscillation on the thermal stress and fatigue damage of the tube was studied in this paper