抄録
This paper investigates the potential effectiveness of natural circulation-driven coolability (NCDC) as a severe accident mitigative measure. The NCDC can particularly be useful in LWR plants which employ external cavity flooding. The main idea is to provide a simple design solution that facilitates bottom feeding of coolant into the debris bed, and uses steam production in the decay-heated debris bed to drive the two-phase flow natural circulation. We use an analytical one-dimensional model to calculate characteristics of two-phase thermal-hydraulics in porous media. The model employs Lockhart-Martinelli correlations for two-phase flow friction and void fraction, and Ergun's correlation used for single-phase flow resistance. Adaptation and verification of the model are discussed in the paper. Coolability of debris beds with coolant bottom-fed is evaluated for a broad range of conditions. The analysis suggests that the dryout heat flux (DHF) in bottom-fed configurations can be increased by 80% to 160%, when compared to DHF in top-flooding beds.
