Jet impingement in high-energy piping systems, part I: Characteristics and model evaluation

Abstract

Under postulated pipe rupture accidents in nuclear power plants (Loss-of-Coolant Accident or LOCA), jet impingement can occur where the high-energy fluid is discharged and cause damage to the surrounding structures, systems, and components (SSCs). As a part of addressing the potential non-conservatisms in the Standard model ANSI/ANS-58.2 (1988), the current work investigates characteristics of jet impingement in high energy piping systems as in nuclear power plants including pressure distribution within jets, pressure on target, and critical mass flux and performs model evaluation. The pressure prediction using ANSI/ANS-58.2 (1988) as well as critical mass flux models are evaluated using the experimental data available in literature. An organized experimental database with different inlet fluid conditions including subcooled water, saturated water/two-phase (0 ≤ x < 0.7), and saturated steam (x ≥ 0.7) is compiled for data analysis and model evaluation. It is found that a power law can be used to correlate the dimensionless static and stagnation pressures at the center of the free jets, while either a power law or an exponential function can be used to correlate the dimensionless stagnation pressure at the center of the targets in impinging jets. The difference in stagnation pressure between free and impinging jets is negligible for saturated steam and saturated water/two-phase jets, but it is significant for subcooled water jets. From model evaluations, the stagnation pressure within the saturated steam jets can generally be predicted well by the Standard model. Although stagnation pressures at far distances (z* > 3.3) can be underestimated, the dimensionless pressures at these axial locations are below 0.07. For saturated water/two-phase jets, the stagnation pressure can be predicted well using the Standard model for the large-scale test data (D > 0.28 m) but are underestimated at some axial locations for the medium- and small-scale test data (D < 0.15 m). Significant overestimation in stagnation pressure is observed for subcooled water jets with high degree of subcooling, which is because the critical mass flux is overestimated using Homogeneous Equilibrium Model (HEM). For subcooled water jets with low degree of subcooling, HEM underestimates the data. Different from HEM, Henry-Fauske model always overpredicts the experimental data, where the degree of overestimation increases as the degree of subcooling decreases. The critical mass flux for saturated steam jets and saturated water/two-phase jets can be predicted well by isentropic expansion model and HEM, respectively.