Steam separators are a common component found in many operating nuclear reactors. In one type - the boiling water reactor (BWR) - steam is produced directly in the reactor core and then transferred to a turbine to produce electricity. However, before reaching the turbine the BWR relies on steam separators to remove excess liquid water from the steam because any droplets trapped in the steam flow can contribute to turbine corrosion and early failure. The pressures within a BWR are very high (over 1000 psi or 7 MPa) which makes direct observation of the flow impossible. Using high resolution tools like PHASTA, we can simulate the two-phase flow within these components. PHASTA directly solves the incompressible Navier-Stokes equations in conjuction with the Level Set method which allows PHASTA to resolve individual droplet/bubble interactions. This allows us to study steam separators 'virtually'.This video visualizes the swirling two-phase flow that occurs within a full 360 degree model of a steam separator with one 'Pickoff Ring'. The swirling flow creates a centrifugal force that pushes the liquid water to the side walls of the separator. The flow then encounters the pickoff ring which directs the liquid water out the separator back down to the bottom of the reactor pressure vessel. Our simulations are focused on the behavior of the two-phase flow around the pickoff ring entrance because this contributes to 2 important effects - Carryover and Carryunder. 'Carryover' refers to any liquid water that bypasses the steam separator and other drying components and reaches the turbine - contributing to turbine damage. 'Carryunder' refers to the steam that is captured by the liquid film traveling into the pickoff ring. This trapped steam has negative effects on the ability of the reactor to operate in natural circulation mode.High resolution simulations like this one provide important flow data that is extremely difficult to obtain experimentally. This data can be used to create new accurate low-resolution turbulence or system-level models that can predict the average flow behavior within steam separators at a fraction of the cost of high resolution simulation.
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