An Experimental Study on Two-Phase Flow Instability in Once-Through Steam Generator Used in SFR

Abstract

Steam generator is a critical component of sodium-cooled fast reactor (SFR). The availability of reactor on power is mainly dependent on safe and stable operation of steam generator. Once-through type integrated steam generators are susceptible to two-phase flow instabilities due to the huge change in specific volume of feed water/steam flowing through a single tube. These flow oscillations may cause tube damage, disturb the control system and affect local heat transfer characteristics. It becomes of utmost importance to identify stable operating regimes of SFR steam generators to avoid such failures. Towards this, experiments are conducted on a model steam generator to establish system characteristics at various loads and to study the thermal hydraulic behavior at reduced pressures. At 20% load, ‘pressure-drop vs. water flow rate’ characteristic curve reveals that the system is statically unstable. Detailed experimental investigations suggest that a stable operation of steam generator can be achieved at reduced system pressure with a higher degree of superheat.