Evaluation of phenomenological dnb models for rod bundle geometries

摘要

Seven phenomenological DNB models based on the liquid sublayer dryout and the bubble crowding mechanisms have been evaluated for the square array rod bundles at PWR conditions. The local thermal hydraulic conditions were calculated by the COBRA-IV-I code, and it was assumed that the enthalpy and mass velocity distribution in the test bundle would not be changed at different power levels. A simplified method, which has been proposed for the prediction of CHF in rod bundles from round tube CHF correlations without detailed subchannel analyses, was also applied with the phenomenological models. In view of the prediction accuracy and the applicable range, Lin model shows the best result among phenomenological DNB models assessed in this study. The parametric trends of phenomenological DNB models, however, are somewhat abnormal comparing to experimental data. So it can be argued that the existing phenomenological DNB models are rather empirical than theoretical so far.