A parametric study was performed in which the singleand two-phase mixing factors that control crossflow inthermal hydraulic subchannel codes were varied todemonstrate the impact on void fraction distributions andthe multiplication factor in a BWR fuel assembly model.The CASL computational tools MPACT and CTF havebeen coupled together in VERA-CS and were used toperform neutronic and thermal hydraulic calculations fora single BWR fuel assembly model with varying degrees ofcrossflow. The single-phase mixing factor was varied from0 to 0.0215. A constant two-phase mixing correction factorof 5.0 was used so that the two-phase mixing factor wasvaried from 0 to 0.1075 in the study. It was found that eachmixing factor case had a relatively similar average axialvoid fraction profile, but the cases with lower mixingfactors showed a larger void fraction difference on asubchannel-by-subchannel basis. Increasing the mixingfactor led to an increase in the infinite multiplication factorfor the system. The results from this study demonstratesome of the benefits to using a 3-D pin-resolved, thermalhydraulic-and-neutronic coupled code like MPACT/CTFcompared to other methodologies commonly used inreactor licensing.
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