EFFECTS OF PARALLEL CHANNEL INTERACTIONS ON TWO-PHASE FLOW SPLIT IN NUCLEAR REACTORS

Abstract

Tests were performed to examine the mutual effects of parallel channel on the pattern of flows into or out of a pair of vertical channels, which have a common upper and a common lower plena, when two-phase flow mixtures are introduced through the plena. The tests would aid the development of a realistic transient computer model for tracking the distribution of two-phase flows into the multiple parallel channels of a Nuclear Reactor, during Loss of Coolant Accidents (LOCA), and were performed at the General Electric Nuclear Energy Division Laboratory, California.

The test channels consisted of two 5.22m long *25.4mm o.d. *23.6mm i.d. stainless steel tubes, with unequal orificing at the bottom, and equal orificing at the top. Provisions were made for electrical resistance heating of 3.5m of each tube, and for visual observation of flows into the tubes. Test fluids were steam and saturated water, and system pressures varied from near atmospheric to a little over 1.7 bar. The method of introducing the flows was varied so as to simulate different flow phenomena which might occur during a loss of coolant accident. Steady flow configurations with both channels in co-current up upflow, or one channel in co-current upflow and the other in downward liquid flow, or one channel in co-current upflow and the other in counter-current flow, were obtained. Flow configurations showed a hysteresis and were history dependent. They depended also on the relative channel orifice restrictions, the state of two-phase mixture in each channel at the start of flow, the manner of initiation of the flows, and on the heat addition rates to the channels.