An experimental analysis of subcooled leakage flow through slits from high pressure high temperature pipelines

The work presented here is an experimental investigation of the critical flashing flow of initially subcooled water through circumferential slits in pipes. The study provides first hand information about the prediction of leak flow rates in piping and pressure vessels retaining high temperature and high pressure. The dedicated experimental facility loop simulates the thermal hydraulic condition of Pressurized Heavy Water Reactors (PHWR). The critical flow characteristics found for varying leakage cross sections at different stagnation pressure and different degree of subcooling has been demonstrated in this paper. A marked decrease in mass flux has been found as subcooling decreases for a fixed stagnation pressure. More observation has revealed that the tighter slits or openings with very short duct as small as 0.8 cm flow length have different flow behavior than greater opening dimensions or with longer flow channels or that for nozzles. The critical flow has been seen to occur at higher pressure differentials along the flaws and prominent changes in the flow rate is reported to occur with varying dimensional parameters of the slit or cracks.

► Leak-before-break analysis for Nuclear Reactor piping demonstrate it's integrity for leakage size cracks . validation of critical flow model for cracks is a requirement.
► Slits on pipe simulates the cracks with known flow area thus reducing the uncertainty on flow area.
► Slit experiments with Pressurised Heavy Water Reactor conditions show dependency of flow on upstream pressure and subcooling as expected.
► Increase in flow area increases flow rate though the mass flux decreases due to L/Dh effect.
► RELAP5 code's flow model largely under predicts the flow to an extent of 20-25%.