Validation of COBRA-TF critical heat flux predictions for a small-hydraulic-diameter geometry under natural boiling conditions

摘要

Critical heatflux (CHF) at a natural boiling condition is an important phenomenon for a research reactor having a small-hydraulic-diameter geometry under a large-break loss-of-coolant accident condition. Accurately predicting the CHF under this condition is very important; therefore, the CHF models used in the best-estimate codes must be validated using appropriate experimental data for a given geometry. The present work focuses on validating the CHF calculations and models within the (CO) under bar olant (B) under bar oiling in (R) under bar od (A) under bar rrays-(T) under bar wo (F) under bar luid (COBRA-TF) code by simulating two sets of experiments, which were performed in tubes and annuli with different length-to-diameter ratios. In this work, the co-current upflow and downflow correlations developed by Mishima and Nishihara and Holowach et al. and Zuber correlations for the CHF used in COBRA-TF are validated against the experimental data obtained by Monde and Yamaji and Islam et al. Conclusions on the predictive capability of COBRA-TF for the CHF calculations for small-hydraulic-diameter geometry under natural boiling conditions are provided with the description of the correlations and models used.