Development of severe accident evaluation technology (Level 2 PSA) for sodium-cooled fast reactors, 5; Identification of dominant factors in ex-vessel accident sequences

ナトリウム冷却高速炉の炉心損傷評価技術(レベル2PSA)の開発,5; 格納容器内事象における支配因子の摘出

大野 修司  ; 清野 裕 ; 宮原 信哉  

Ohno, Shuji; Seino, Hiroshi; Miyahara, Shinya

ナトリウム冷却大型高速炉の炉心損傷事故の影響が原子炉容器外まで及ぶ場合における事故進展を検討し、CONTAIN/LMRコードを使用した感度解析によって事故進展の支配現象・支配因子を調べた。除熱源喪失時に想定される事故進展を対象とした解析から、ナトリウム蒸気の漏えい速度及びナトリウム・コンクリート反応の規模が重要な支配因子であることを明らかにするとともに、それらが格納容器へ与える圧力負荷に関して定量的な情報を整理することができた。

Typical ex-vessel accident sequences in the JSFR are discussed in this paper and dominant behaviors or factors in the sequences are investigated through parametric calculations using the CONTAIN/LMR code. Scenarios to be focused on are, (1) sodium vapor leakage from the reactor vessel and (2) sodium-concrete reaction, which are both to be considered in the LOHRS accident category and might be followed by an early containment failure due to the thermal effect of sodium combustion and hydrogen burning respectively. The calculated results clarify that the sodium vapor leak rate and the scale of sodium-concrete reaction are the important factors to dominate the ex-vessel accident progression. In addition, the results also provide the specific information such as pressure loading value to the containment and the timing of pressurization, which is indispensable as technical base in Level 2 PSA for developing event trees and for quantifying the accident consequences.