炉心損傷時の炉心物質再配置挙動評価手法の開発,2; 液-液接触条件における溶融炉心模擬物質のデブリ化距離の測定評価

Development of assessment method to evaluate the material relocation behavior in the core disruptive accident of FBR, 2; Measurement and evaluation of the distance for fragmentation of molten core simulant in liquid-liquid direct contact

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

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へ流出した溶融炉心物質がデブリ化するまでの距離(デブリ化距離)の評価手法を開発するため、低融点合金融体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試験を行った。本試験では、融体の流出口径を増加させると水中における液柱状融体のデブリ化距離の測定値が長くなる傾向が見られたが、各々の測定値は既往研究の代表的な実験相関式に基づく評価値に対し1/10程度に短かくなる結果が得られた。本試験結果に基づき、液-液接触状態で急速な蒸気泡発生が生じる条件の下では、液柱状融体が従来評価に比べ大幅に短い距離でデブリ化されることを確認した。

In order to develop an evaluation method of the distance for fragmentation (debris formation) of molten core material discharged into the lower sodium plenum during core disruptive accidents in sodium-cooled fast reactors, a fundamental experiment was carried out, in which molten alloy (melt) and water were employed to simulate liquid-liquid direct between molten core material and sodium. Experimental results show that measured distances for fragmentation of melt column tended to increase with the increase of discharge diameter. However, the measured distances were approximately 10% lower than predictions by the existing representative correlation. Based on the results of this fundamental experiment, it was understood that the distance for fragmentation can be significantly reduced in conditions where liquid-liquid direct is established and thus vapor formation occurs intensively.