Assessment of two-phase interchannel mixing models for BWR and PWR conditions

In this paper, we assessed the interchannel mixing models currently available in MATRA (Yoo et al., 1999), a subchannel analysis code modified based on COBRA-IV-I (Stewart et al., 1977), for application to two-phase flow conditions of both BWR and PWR fuel rod bundles. By recalculating selected test cases from the NUPEC BFBT benchmark (Neykov et al., 2006) and the ISPRA benchmark (Herkenrath et al., 1981), prediction accuracy of the equal-volume-exchange of turbulent mixing and void drift (EVVD) model implemented in MATRA was found to be not satisfied for application in the dispersed bubbly flow regime under PWR pressure level. Since the EVVD model is adopted in most state-of-the-art subchannel analysis codes in similar manners as in MATRA, we believe that an improvement of the EVVD model should be carried out in the future. Finally, based on results obtained in the current study, we discussed the drawbacks of the EVVD model and pointed out possible aspects that should be considered for improvement.