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

JSFRにおける炉心崩壊事故時の上方燃料流出にかかわる試験研究; 炉外可視化基礎試験の結果

松場 賢一  ; 磯崎 三喜男; 神山 健司  ; 飛田 吉春

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

JSFRでは、炉心崩壊事故時の炉心内部での溶融燃料の急速な凝集による厳しい出力バーストの回避を目的として、溶融燃料を集合体単位で流出させる「内部ダクト付き燃料集合体」の導入を検討している。現在は、炉心上端部に向かって開口(下端部はほぼ閉止)を有する設計オプションを選択している。本研究では、内部ダクトを通じた燃料流出にかかわる物理メカニズムを解明するため、模擬物質(低融点合金及び水)を用いた炉外可視化基礎試験を実施した。本基礎試験を通じて、融体の流出初期段階でのダクト内の冷却材のボイド化、及び実機相当ダクト体系での蒸気に駆動された高密度融体の上方流出挙動を確認できた。

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.