The effect of riser on the characteristics of natural circulation for boiling two-phase flow

Natural circulation BWR such as GE-SBWR is proposed for next generation LWRs. A long riser is installed in order to increase recirculation flow rate and to stabilize the system. Since the long riser generates the great part of recirculation force, the flow characteristics should enough be estimated in order to improve reliability and performance, and to consider feasible range of power levels. In this paper flow characteristics of natural circulation loop including a long riser were investigated analytically and experimentally under condition of atmospheric pressure. In the loop with the long riser the recirculation flow oscillation can occur in the range that the oscillation dose not occur with a short riser, though it is said that the long riser stabilizes the system. The boiling induced pressure drop in the derection of height occur more readily with increasing the riser length and with decreasing the system pressure. (author)