Fundamental experiment on the distance for fragmentation of molten core material during core disruptive accidents in sodium-cooled fast reactors

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

In order to develop an evaluation method of the distance for fragmentation of molten core material discharged into the lower sodium plenum during core disruptive accidents (CDAs) in sodium cooled fast reactors, fundamental experiments were conducted using a high-density melt and water as simulants for the molten fuel and coolant, respectively. The melt was discharged into a water pool through a nozzle (inner diameter: from 30 mm to 150 mm) under a simulated CDA condition where a liquid-liquid direct contact is maintained between the melt and water. The present results showed that measured distances for fragmentation were limited to approximately 10 percent of predictions by the existing representative correlation, and that vapor expansion with pressure buildup near the melt could facilitate the fragmentation and thus contribute to the reduction of the distance for fragmentation. Through the fundamental experiments, useful knowledge was obtained for the future development of an evaluation method.