Jet impingement in high-energy piping systems, part II: Model improvement and guidance development

The Standard model in ANSI/ANS-58.2 (1988) has been widely employed in the design and safety analysis of nuclear power plants for jet impingement under postulated pipe rupture accidents. However, the potential non-conservatisms presented in Standard Review Plan (2015) need to be addressed when evaluating this model. The current work aims to improve the model on jet prediction including jet geometry and stagnation pressure, as well as to address the potential non-conservatisms. Based on the model evaluation results in Part I, new correlations for the jet core length and stagnation pressure in subcooled water and saturated water/two-phase jets are implemented to replace the existing correlations in the Standard model. It is shown that the revised code with the newly developed correlations predicts the stagnation pressure generally higher or conservatively for all conditions investigated. On the potential blast wave effect, the current work develops an approach to quantify the over-static and reflected pressures using the equivalent weight of TNT approach in literature. To employ this approach, the released energy in the equivalent of TNT needs to be determined from jet impingement. This energy is calculated using the vessel burst energy concept with conservative assumptions in the current work. For jet geometry, dynamic models to predict the jet spreading angle for saturated steam jets are compared with the Prandtl-Meyer angle for under-expanded supersonic jets. It is found that the jet spreading angle for saturated steam jets in the Standard model generally agrees with the dynamic model in literature for a wide range of initial vessel stagnation pressure conditions. Regarding the pressure distribution within jets, it is confirmed that edge-peaking pressure profiles can be observed for saturated steam jets at far distances from the break plane (z > 3.3 D); however, the dimensionless pressures at these locations are generally less than 0.07. Regarding the jet dynamic loading effect, the literature review suggests that dynamic amplification and resonance of impinged downstream structures and components might not occur for jet impingement in nuclear power plants.