Experimental and Theoretical Analysis of Subcooled Water Discharge Through Simulated Steam Generator Tube Cracks

The steam generator (SG) tubes represent a major fraction of the reactor primary coolant pressure boundary surface area in both Canadian pressurized heavy water reactor (CANDU) reactors and pressurized water reactor (PWR). There is very limited data on the steam generator tube leak rate measurement. Most studies of subcooled choking flow are related to long tubes with L/D greater than 15. Also, all of those data have a channel length greater than 10 mm, which is not indicative of steam generator tubing. Steam generator tubes have a wall thickness typically less than 3 mm. Experiments were conducted on choking flow for various simulated crack geometries for vessel pressures up to 7 MPa with various subcoolings. Measurements were done on subcooled flashing flow rate through well defined simulated crack geometries with L/D at ∼2 and 5–6. Both homogeneous equilibrium and non-equilibrium mechanistic models were developed to model two-phase choking flow through slits. A comparison of the model results with experimental data shows that the homogeneous equilibrium based models grossly under predict choking flow rates in such geometries, while homogeneous non-equilibrium models greatly increase the accuracy of the predictions.

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