Assessment of Two-Phase Flow Predictability of 3D Components in MARS-KS and TRACE in Rod Bundle Geometry

Abstract

This study aims at assessing the 3D components in MARS-KS and TRACE, in order to confirm the appropriate capability of both system codes under the two-phase flow conditions in the rod bundle geometry. For the assessment, two-representative separate effect tests, namely GE 3X3 and PSBT bundle, were employed, and code-to-code comparison has been made against the experimental results, statistically. From the assessment, it was revealed that both codes did not predict the phasic distribution of bundle, appropriately. It was observed that TRACE significantly overpredicted vapor distribution of the experiments compared to MARS-KS. The overcalculation of TRACE was attributed from the restricted crossflow calculations compared to MARS-KS, as it imposed large interfacial drag applying drift flux model for the crossflows. In case of MARS-KS, it also featured inappropriate crossflow behaviors when compared to the experimental data. This result was obvious since both codes neglected the presence of secondary flows due to substantial flow disturbances by rod bundle. Employing the subchannel mixing model into MARS-KS, it was observed that more accurate phasic distribution could be simulated by the code, consequently, improving the overall code predictability. These findings clearly indicated that the code predictions were significantly affected by the accurate crossflow predictions in bundle-scale level. Hence, the improvements to the crossflow models of both codes were necessary for bundle-scale analyses.