Study of flow instability in parallel channel system for water cooled blanket

Abstract

Water is adopted as coolant in many blanket concepts, and the flow condition is designed based on its use in boiling water reactor (BWR) and pressure water reactor (PWR). The flow instability may occur in the water cooled blanket when water undergoes two-phase flow during steady state or under some accidents. The flow rate in one channel will change and oscillate, while the pressure is still constant. In this study, the research of flow instability in parallel channels, including flow excursion and flow oscillation, is performed using the thermal-hydraulic analysis code RELAP5. The phenomenon of flow instability is detected by the method of small disturbance. The different conditions of BWR and PWR are investigated. The effect of arrangement of parallel channels, vertically and horizontally, is also studied under 7 MPa for BWR condition and 15.5 MPa for PWR condition. Finally, the stability map of the four conditions is obtained. The analysis shows that the flow is more stable under PWR condition since the equilibrium quality of stability boundary is higher. The arrangement of coolant channels has different influences under different conditions. Under PWR condition, it will stabilize the system if the flow channels are horizontally arranged. However, the influence of the channel arrangement on the flow boundary is limited under BWR condition. The research work can provide an important reference for design and operation of water cooled blanket, especially for the consideration of high heat removal.