Identification of the accident sequences for the evaluation of the effectiveness of severe accident measures on prototype Sodium-cooled Fast Reactor

プロトタイプ高速炉におけるシビアアクシデント対策の有効性評価のための事故シーケンスの同定

小野田 雄一 ; 栗坂 健一 ; 堺 公明

Onoda, Yuichi; Kurisaka, Kenichi; Sakai, Takaaki

The accident sequences beyond design basis to be considered for the prototype Sodium-cooled Fast Reactor (SFR), which is now under development in Japan Atomic Energy Agency (JAEA), are identified in order to confirm the effectiveness of the measures against severe accidents. Internal and external events are considered as potential initiator of severe accidents. Earthquake and tsunami are focused on as the external events in light of the accident at the Fukushima Dai-ichi Nuclear Power Station. Probabilistic Risk Assessment (PRA) and/or its alternative approach are taken for the comprehensive analyses of the accident sequences. At first, four important accident sequence groups are identified; anticipated transient without scram, loss of reactor sodium level, protected loss of heat sink and loss of all alternating current power sources. Then accident sequence to be evaluated is extracted from corresponding accident sequence group. Severe accident measures which are composed of installing hardware or constructing emergency operator procedure, and which are intended to minimize the risk of radioactive release, are also identified for each accident sequence. In order to confirm the effectiveness of those severe accident measures prepared for prototype SFR, deterministic safety evaluations of those accident sequences should be carried out.