High Energy Line Breaks (HELBs) inside nuclear reactor containment are recognized as challenges to Pressurized Water Reactor (PWR) nuclear power plants arising from the collateral damage due to insulation, fireproofing, coatings, and other miscellaneous materials (such as tags, stickers, signs, etc) which are shredded and transported during the event. These materials, as well as latent debris (dirt and dust) will be washed towards the containment floor and the recirculation sump screens by flow from both the HELB and the containment spray headers. This debris, if washed towards the recirculation pumps, could potentially impede the performance of the ECCS system. To evaluate transport of material towards the sump and the potential for degradation in performance of the ECCS system, Computational Fluid Dynamics (CFD) has been used to predict the flow patterns and energy levels in the containment pool during the recirculation phase of the event. Further, a unique methodology has been applied to correlate the CFD results with material-specific laboratory flume data and predict the volume of material transported to the sump screens. The predicted volume of debris transported to the sump screens is then used to determine if there is sufficient suction head for the pumps to operate without the potential for cavitation. In this paper, the CFD-based methodology used to predict material transport to the sump screens is discussed and the results of a prototype containment analysis are presented. Of particular interest is the analytical method for introducing the HELB flow into the containment pool and the quasi-steady treatment of the water surface to simulate the gradual filling of the pool. Coupling of the velocity and kinetic energy fields from the CFD simulations with material-specific incipient tumbling velocities (as predicted during a series of laboratory flume tests) are presented and used to demonstrate overall material transport to the sump screens.
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