In sodium-cooled fast reactors (SFRs), one of the design issues is the suppression of reactivity disturbances caused by non-condensable gas bubbles passing through the core, which are entrained into the primary coolant system due to cover gas entrainment and dissolution. The authors has developed an evaluation method for the gas transition behavior of non-condensable gas in the primary circuit (SYRENA). In this study, preliminary analyses were carried out to understand the bubble transfer behavior in the cold plenum of the pool-type SFR. Trajectories of non-condensable gas bubbles were obtained from three-dimensional CFD analyses applying Discrete Phase Model to grasp the behavior of gas bubbles in the coolant. As the result of sensitivity analyses regarding bubble radius flowing into the cold plenum, it was clarified that significant number of gas bubbles are released from the free surface in the cold plenum. The release rate of bubbles from the free surface showed an increase according to the increase of bubble radius, and the release rate also showed an asymptotic increasing behavior in the large bubble radius cases.
MATSUSHITA et al. (Wed,) studied this question.