Experimental study on upward fuel discharge during core disruptive accident in JSFR; Results of an out-of-pile experiment with visual observation

Matsuba, Kenichi  ; Isozaki, Mikio; Kamiyama, Kenji  ; Tobita, Yoshiharu

The introduction of Fuel Assembly with Inner Duct Structure (FAIDUS) is being studied to prevent the formation of a large-scale molten fuel pool within a reactor core, which is one of factors leading to the severe power excursion during Core Disruptive Accidents of Sodium-cooled Fast Reactors. In the current reference design for FAIDUS, the top end of the inner duct is open whereas the bottom end is closed, and therefore it is expected that the molten fuel will be discharged from a reactor core toward an upper sodium plenum through the inner duct. An out-of-pile experiment, in which a high-density melt simulating the molten fuel was injected into a simulated inner duct structure, was carried out in order to clarify the fundamental mechanism for upward discharge of a high-density melt. Through the experiment, upward melt discharge driven by coolant vapor flow was visually observed, and the fundamental mechanism for upward discharge of a high-density melt was clarified.