Formulation of a fully implicit numerical scheme for simulation of two-phase flow in a vertical channel using the Drift-Flux Model

This paper introduces a new fully implicit numerical scheme to simulate two-phase flow in a vertical channel. Two-phase flow is widely associated with the nuclear systems and therefore accurate prediction of the void fraction as a key thermo-hydraulic parameter is crucial in operational and safety analysis. The Drift-Flux Model (DFM) is applicable to a wide range of thermal-hydraulic phenomena in an integral pressurized and boiling water reactors. However, to obtain an accurate and stable solution is a challenge task for successful application of the model. The trend toward the more accurate simulation requires advanced numerical methods. The efficiency of the recently develpoed Jacobian-free Newton-Krylov (JFNK) method as an advanced fully implicit solver have been demonstrated in the published literature. However, there are still unsolved problems with this method. Therefore, a much simpler, more reliable and a fast fully implicit model is developed as a variant of Newton method. The objective of the present study is to investigate the validity, accuracy and CPU usage of the proposed model. Also, good agreement was found between our results and those of the experimental data and the RELAP5 code. Comparison of our results with those of JFNK proved viable for handling thermo hydraulic transients without stability constraints. It is simpler, more accurate and faster than the JFNK method.