Steady-State Two-Phase Header Flow Mndcl

Abstract

The safety analysis of CANDU reactors includes accident scenarios in which two-phase fluid is present in the inflow header. This may occur with "normal" pump operation as well as after forced circulation is lost and two-phase thermosyphoning is established. During periods in which the inflow header is partially voided. it is sometimes desirable to know the flow distribution among feeders and specifically, to determine whether any of the feeders are exposed to single-phase steam or a high quality two-phase mixture. A model has been developed at Ontario Hydro which predicts void distributions in the inflow header, feeder flowrates. and void fractions at feeder entrances under conditions of steady-state. two-phase flow. Steady-state, two-phase tests conducted in the Large Scale Header Facility (LSHF) at Stern Laboratories Inc. provide an experimental data base for validation of the inflow header model. The LSHF inlet and outlet headers are full scale. half-length Pickering NGS headers. A two-phase mixture is injected via one or two turrets into the preheated loop at system presures of 1, 2 or 5 ma. Water injection flow rates vary from 30 to 60 kg/s at qualities up to 6 percent. The header model captures the physical behaviour of two-phase flow in the inflow header and agreement with experimental data is good. The model is described and model predictions are compared with experimental results.