Numerical study on influence of Ohnesorge number and Reynolds number on the jet breakup behavior using the lattice Boltzmann method

In a core disruptive accident of a sodium-cooled fast reactor, the considerable amount of fuel in the core region may melt, and be discharged into the coolant like a jet. Hence, it is necessary to understand the jet breakup behavior from the viewpoint of the post-accident heat removal. In order to clarify the mechanism of jet breakup caused by the hydrodynamic interaction, we simulated the injection of a jet into a coolant using the lattice Boltzmann method for two-phase fluid which can represent the spontaneous interfacial behavior. In the simulation, we changed the Reynolds number of the jet and the viscosity ratio between the jet and the coolant, and observed their influence to the interfacial behavior. By observing the interfacial behavior, we found that the wave formation and fragmentation at the side of the jet were suppressed when the Reynolds number becomes small, and cognized the importance of considering the influence of the viscosity of a coolant to the jet behavior. (author)