ANALYSIS OF FLOW INSTABILITIES AND THEIR ROLE ON CRITICAL HEAT-FLUX FOR 2-PHASE DOWNFLOW AND LOW-PRESSURE SYSTEMS

A stability analysis of a Row boiling two-phase low pressure and downf low system relative to the occurrence of critical heat flux has been c arried out. The problem formulation is based on a time and area averag ed one-dimensional drift flux model, with the necessary constitutive e quations. A characteristic equation is obtained to predict the onset o f flow excursion and density wave oscillations. By non-dimensionalizin g the characteristic equation, important groups governing the system s tability are determined, The results of the analysis are useful in det ermining the region of stable operation for downflow in the Westinghou se Savannah River Site Reactor and in avoiding the onset of Row excurs ions and density wave oscillations. The analytical results for flow ex cursion are compared with the Babcock and Wilcox flow excursion experi mental data with a Savannah River Mark 22 fuel assembly mockup.