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

ナトリウム冷却高速炉の炉心損傷時における溶融炉心物質のデブリ化距離に関する基礎試験

松場 賢一  ; 磯崎 三喜男; 神山 健司  ; 飛田 吉春; 鈴木 徹

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

ナトリウム冷却高速炉の炉心損傷時に原子炉容器下部プレナムナトリウム中へ流出した溶融炉心物質が微粒子状固化物(デブリ)になるまでの距離(デブリ化距離)に関する評価手法を開発するため、模擬物質(低融点合金と水)を用いて溶融炉心物質とナトリウムの液-液接触状態を模擬した基礎試験を行っている。本基礎試験ではデブリ化距離の実測値が従来予測に比べ10%程度以下の短い距離でデブリ化される結果となった。試験結果の分析に基づき、このデブリ化距離の大幅な短縮には液-液接触状態からの蒸気泡の膨張に伴う急速なデブリ化が寄与した可能性を明らかにした。本基礎試験を通じてデブリ化距離評価手法開発に有益な知見が得られた。

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.