NUMERIC STUDY OF VOID DRIFT UNDER PWR CONDITIONS WITH CFD APPROACH

摘要

This paper is devoted to the numerical study of void drift under PWR conditions with help of two-phase CFD approach. Void drift model available in state-of-the-art subchannel codes, for instance MATRA, is based on the equal-volume-exchange turbulent mixing incorporating void drift concept proposed by Lahey and Moody(hence referred to as the EVVD model). However, turbulent mixing and void drift are not clearly separated in the widely adopted EVVD approach. The same effective mixing velocity is applied to the two mixing effects that are induced by different physical mechanisms. In the present paper, two-phase CFD approach was employed to improve void drift modeling for subchannel analysis. We proposed a new phenomenological two-phase interchannel mixing model, with which the effect of void drift can be separated from CFD simulation results. Based on systematic CFD simulations covering typical PWR conditions, correlations were proposed to describe both void fraction distribution at equilibrium state and effective mixing velocity due to void drift. Finally, the proposed void drift model was implemented in MATRA for validation calculation with selected test cases of a rod bundle benchmark.