Experimental study on breakup and fragmentation behavior of molten material jet in complicated structure of BWR lower plenum

Saito, Ryusuke*; Abe, Yutaka*; Yoshida, Hiroyuki  

To estimate the state of the reactor pressure vessel (RPV) of Fukushima Daiichi Nuclear Power Plant, it is important to clarify the breakup and fragmentation of molten material jet in the BWR lower plenum by a numerical simulation. To clarify the effects of complicated structures (e. g., the control rod guide tube in the BWR lower plenum) on the jet behavior experimentally and validate the simulation code, we conduct the visualized experiments and surrounding velocity profiles of the jet were observed by the backlight method and the particle image velocimetry (PIV) method. From experimental results using the backlight method, it was clarified that the jet tip velocity depends on the condition whether complicated structures exist or not and also clarified that the structures prevent the core of the jet from expanding. From measurements by the PIV method, the surrounding velocity profiles of the jet in the complicated structures were relatively larger than the condition without structure. Finally, fragmentation diameter measured in the present study agreed well with the theory suggested by Kataoka and Ishii by changing the coefficient term. Thus it was suggested that the fragmentation mechanism was mainly controlled by the shearing stress.