Numerical Analysis of Dryout Phenomena in Light Water-Cooled Nuclear Reactors using Particle Method

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In Boiling Water Reactors (BWRs), annular mist flow appears in the upper part of the core. Dryout is a limiting condition of thermalhydraulic design. It is important to analyze dry out accurately for the reactor design and safety. Moving Particle Semi-implicit (MPS) method has been developed by the present researchers. The MPS method does not need meshes, so that droplet separation and merging are easily analyzed. In the present study, direct simulation of dry out was carried out using the MPS method.Dryout phenomenon consists of the deposition process where droplets are absorbed by the liquid film flowing on the fuel reds, and the entrainment process where droples are released from the liquid film. First, single droplet behavior in the deposition process was analyzed by the MPS method. When the droplet diameter is small or the impact velocity is slow, the droplet is totally absorbed by the liquid film. When the droplet diameter is large or the impact velocity is high, the droplet impact disturbs the liquid film and new droplets are generated. This new droplets (re-entrainment) cannot be neglected in the Boiling Water Reactor (BWR) conditions.A particle-mesh hybrid method was developed based on the finite volume method and the particle method (MPS method). Gas-liquid two-phase flow can be analyzed efficiently using the hybrid method. A low-Reynolds number k-ε model was incorporated into this hybrid method. Simulation of liquid film flow and instability on the fuel rods in BWR cores using the hybrid method.In this study, numerical methods have been developed to analyze the basic processes in the dryout phenomenon m the BWR conditions. Anew knowledge about the re-entrainment process was also obtained.