Jet Impingement in High-Energy Piping Systems (NUREG/CR-7275)

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Publication Information

Manuscript Completed: September 2020
Date Published: March 2021

Prepared by:
S. Kim, M. Ishii, and R. Kong

Thermal-hydraulics and Reactor Safety Laboratory
School of Nuclear Engineering
Purdue University
West Lafayette, IN 47907-2017

Andrew Ireland, NRC Project Manager

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Abstract

Appendix A of the Standard Review Plan (U.S. Nuclear Regulatory Commission, 2015) identified several potential non-conservatisms in the existing models for jet impingement in high-energy piping systems as in nuclear power plants, with respect to (a) blast wave formation, (b) jet plume expansion and zone of influence, (c) distribution of pressure within the jet plume, and (d) jet dynamic loading. The current work performs a comprehensive literature review and model evaluation to aid in addressing these potential non-conservatisms. Based on the results, the model is revised and model guidance is developed.

The literature review covers important jet impingement phenomena, experimental studies, as well as important models and CFD simulations of jet impingement. It is found that key phenomena including jet expansion, jet impingement, and critical flow are reflected in the existing models, but the potential blast waves and jet dynamic loading are not considered in modeling jet impingement in nuclear power plants. The publicly available experimental studies are reviewed and an experimental database is established for data analysis and model evaluation. The parameters including pressure, break size, and axial distance are non-dimensionalized such that the effects of the initial fluid condition and break size can be investigated. Using this database, correlations are developed to predict the static and stagnation pressures at the center of jets with different initial fluid conditions and break sizes.

Important jet impingement models including the Standard model (ANSI/ANS-58.2, American Nuclear Society, 1988) and the two-phase jet load model (NUREG/CR-2913, Weigand, 1983) are evaluated. It is found that the stagnation pressure for saturated steam jets can generally be predicted well by the Standard model. The stagnation pressure for saturated water/two-phase jets can also be predicted well using the Standard model for the large-scale test data (D > 0.28 m), but are underestimated for medium- and small-scale test data (D < 0.15 m). Significant overestimation in stagnation pressure is observed for subcooled water jets in Region 1 with a high degree of subcooling (ΔT > 40 °C), which is because the critical mass flux is significantly overestimated using the Homogeneous Equilibrium Model (HEM). In addition, the distance between the break plane and the asymptotic plane is also investigated. It is found that the Standard model can predict this distance well for saturated steam jets, but overpredicts that with 100% difference for saturated water/two-phase and subcooled water jets. Although this will predict a larger zone of influence, the pressure within the jets is still predicted conservatively in Regions 2 and 3.

Based on the results of the literature review and model evaluation, the Standard model is revised and model guidance is developed to address the potential non-conservatisms. The revised model shows improved predictions for stagnation pressure. For the potential blast wave effect, approaches based on the equivalent weight of TNT are developed to quantify the static overpressure and the reflected pressure. For jet geometry, it is found that the jet spreading angle for saturated steam jets in the Standard model generally agrees with the dynamic model (Morita et al., 2016) in literature for a wide range of initial stagnation pressure conditions. Regarding the pressure distribution within jets, it is confirmed that edge-peaking pressure profiles are observed for saturated steam jets at far distances from the break plane (z > 3.3D); however, the dimensionless pressures at these locations are generally less than 0.07. On the potential jet dynamic loading effect, the justifications provided in Kauffman et al. (2019) are reviewed and it indicates that this effect might not occur for jet impingement in nuclear power plants.