A comprehensive, mechanistic heat transfer modeling package for dispersed flow film boiling - Part 1 - Development

Accurate predictions of Dispersed Flow Film Boiling (DFFB) heat transfer are necessary during both the blowdown and reflood portions of a Loss-of-Coolant-Accident to ensure the correct initial fuel rod temperature distribution for the beginning of the reflood phase and ultimately, determining the peak cladding temperature. Numerous correlative, phenomenological, and mechanistic DFFB heat transfer models have been published; however, most of these models make simplifying assumptions that adversely impact their accuracy or are too computationally intensive to implement into current reactor safety codes. A comprehensive, mechanistic heat transfer modeling package has been developed to account for the six interrelated heat transfer paths in DFFB. Highlights of the model include a Lagrangian subscale trajectory based dry contact heat transfer model and a novel method of determining the two-phase convective heat transfer enhancement due to dispersed droplets intermittently altering the local vapor temperature distribution.