Gas entrainment allowance level at free surface and gas dynamics behavior of sodium-cooled fast reactor

Yamaguchi, Akira*; Tatsumi, Eisaku*; Takata, Takashi*; Ito, Kei; Ohshima, Hiroyuki; Kamide, Hideki ; Sakakibara, Jun*

In a sodium-cooled fast reactor, inert gases exist in the primary coolant system either in a state of dissolved gas or free gas bubbles. In the present study, a gas entrainment allowance level at the free surface is discussed and rationalized. The influence of the gas entrainment is evaluated using the void fraction at the core inlet. For the purpose, a plant dynamics code VIBUL has been developed to evaluate the concentration distribution of the dissolved gas and the free gas bubble. It is noted that the background level is already very low in comparison with the induced void reactivity by the void passing the reactor core.