Development of technical basis in the initiating and transition phases of unprotected events for Level-2 PSA methodology in sodium-cooled fast reactors

ナトリウム冷却高速炉のレベル2PSA評価手法のための炉停止失敗事象の起因過程及び遷移過程における技術基盤の整備

山野 秀将   ; 佐藤 一憲 ; 飛田 吉春

Yamano, Hidemasa; Sato, Ikken; Tobita, Yoshiharu

Based on the state-of-the-art knowledge, the headings of these event trees were selected so that dominant factors in accident consequences can be represented appropriately. For each of the headings, available information for the probability quantification were reviewed and integrated as the technical database for the Level-2 PSA. For the transition phase, dominant factors were also identified through parametric analyses. In the Japan Sodium-cooled Fast Reactor, an inner duct is introduced into a fuel subassembly for enhancing molten fuel discharge from disrupted core in the transition phase. The parametric study showed that the analytical case without the fuel discharge through the inner duct resulted in an occurrence of recriticality regardless of the fuel discharge through control-rod guide tubes. This suggests that the fuel discharge through the inner duct is essential to avoid severe recriticality in the transition phase.