Assessment of Choking Flow Models in RELAP5 for Flashing Flow Through Small Cracks

The estimation of leak rates through steam generator tube crack is an important safety parameter. An assessment of the choking flow models in thermal-hydraulics code RELAP5 is performed and its applicability to predict choking flow rates through steam generator tube cracks is addressed. A RELAP5 nodalization was created to model experimental data from literature. It is found that both the Henry-Fauske and Ransom-Trapp models better predict choking mass flux for longer channels. As the length of a channel decreases the both models’ predictions diverge from each other. While RELAP5 has been shown to predict choking flow in large scale geometries, it is not suited well for small channel lengths. In the case of a more conservative approach, where over prediction of mass flux through short channels is best, the Henry-Fauske model would be most appropriate.