Assessment of the Drift-Flux Parameter Correlations Implemented in the Nuclear Thermal-Hydraulic Analysis Code TRACE

The present study assessed the drift-flux parameter correlations implemented in the TRACE code, the flagship thermal-hydraulic analysis code developed by the United States Nuclear Regulatory Commission (US NRC). The code is architected on the basis of a two-fluid model. The interfacial drag force is formulated by the Andersen–Chu approach to avoid the interfacial area concentration dependence on the interfacial drag force. Thus, the interfacial drag force formulation requires the drift-flux parameters, such as the distribution parameter and the drift velocity. The TRACE code adopts different drift-flux parameters for different flow channel geometries, such as pipes and rod bundles. The implemented drift-flux correlations for dispersed two-phase flows are the Kataoka–Ishii drift-flux correlation for pipes and the combination of the Bestion drift velocity correlation and the distribution parameter of unity for rod bundles. Since these correlations were developed before 1990, this paper discusses the validity of these correlations based on data collected after 1990. First, the assessment confirmed that the Kataoka–Ishii drift-flux correlation was valid for beyond-bubbly flows in pipes. The assessment also demonstrated that the Hibiki–Tsukamoto correlation offered improved accuracy compared to the Kataoka–Ishii correlation in bubbly to beyond-bubbly flow in pipes. The distribution parameter set at unity in the TRACE code tended to underestimate experimental values in rod bundles, whereas the drift velocity calculated by the Bestion drift velocity correlation tended to overestimate the experimental data in rod bundles at low-pressure conditions. The tradeoff between the underestimated distribution parameter and overestimated drift velocity resulted in reasonably good predictions. Finally, the assessment demonstrated that the Hibiki–Tsukamoto correlation improved the data prediction accuracy in rod bundles. Considering the future use of the TRACE code for various new nuclear reactor designs and accident scenarios, including low-pressure and low-flow rate conditions, this study recommended replacing the current drift-flux correlations implemented in the TRACE code with the advanced drift-flux correlations. © 2025 Takashi Hibiki and Naofumi Tsukamoto. International Journal of Energy Research published by John Wiley & Sons Ltd.