Flooding and non-equilibrium in counter-current flows with reference to pressurised water reactors
PublisherUniversity of Strathclyde
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During the refill stage of a Loss of Coolant Accident (LOCA) in Pressurised Water Reactor (PWR), the effectiveness with which the emergency coolant penetrates to the lower plenum, and hence to the core, is of paramount importance. This thesis presents the results of experimental and theoretical work carried out at the University of Strathclyde on two 1/10 scale planar test sections of a PWR downcomer annulus. The experiments involved the countercurrent flows of air and water and the data compared with existing flooding correlations for tubes. The comparison revealed the inadequacy of the existing correlations. Use was made of previous experimental results for steam-water mixtures on similar test sections in conjunction with the present air-water data to study condensation effects. Here the non-equilibrium effects were isolated and correlated against the dependent parameters of inlet water flowrate, inlet sub cooling and down comer wall temperature. A theoretical model for the condensation process was developed which gave good qualitative and quantitative agreement with experiment. Its superiority over a current BCL correlation is demonstrated. In the Phase 1 test section arrangement, it was found experimentally thut, as the inlet air flowed upwards against two opposing waterfalls, an Increase in air flowrate caused the water- falls to move Closer together until a critical air flowrate was reached where the waterfalls collapsed. A theoretical model was also developed to define this collapse condition which WuS shown to be analogous to the choked flow of air through a nozzle whose cross sectional nrea vuried with pressure. whilst this phenomenon was not directly related to the PWR refill problem, it was an interesting feature in its own right.