Pressure suppression pool mixing in passive advanced BWR plants

In the SBWR passive boiling water reactor, the long-term post-accident cont ainment pressure is determined by the combination of noncondensible gas pre ssure and steam pressure in the wetwell gas space. The suppression pool (SP ) surface temperature, which determines the vapor partial pressure, is very important to overall containment performance. Therefore, the thermal strat ification of the SP due to blowdown is of primary importance. This work loo ks at the various phases and phenomena present during the blowdown event an d identifies those that are important to thermal stratification, and the sc aling necessary to model them in reduced size tests. This is important in d etermining which of the large body of blowdown to SP data is adequate for a pplication to the stratification problem. The mixing by jets from the main vents is identified as the key phenomena influencing the thermal response o f the suppression pool and analytical models are developed to predict the j et influence on thermal stratification. The analytical models are implement ed into a system simulation code, TRACG, and used to model thermal stratifi cation behavior in a scaled test facility. The results show good general ag reement with the test data. (C) 2001 Elsevier Science B.V. All rights reser ved.