Investigation on natural circulation behavior for decay heat removal in reactor vessel of sodium-cooled fast reactor under severe accident condition, 2; Transient behavior under operations of multiple decay heat removal systems

ナトリウム冷却高速炉におけるシビアアクシデント時の原子炉容器内の自然循環による崩壊熱除去特性の検討,2; 複数冷却器起動時の過渡挙動

相澤 康介 ; 辻 光世 ; 小林 順 ; 栗原 成計 

Aizawa, Kosuke; Tsuji, Mitsuyo; Kobayashi, Jun; Kurihara, Akikazu

ナトリウム冷却高速炉の安全性強化に向けた炉内冷却機器の設計と運用の最適化に資するために、シビアアクシデント時を含む崩壊熱除去特性および熱流動特性を把握する縮尺水流動試験を実施している。本報告では、複数の冷却機器起動が原子炉容器内自然循環挙動に与える影響を把握するために、浸漬型DHX及び貫通型DHXを起動させた過渡試験を実施した結果を示す。試験結果より、一基目のDHX起動により自然循環定常状態を達成した後、二基目のDHXを起動することで、自然循環定常状態における最高温度を一時的に超えることが示された。炉心下部プレナムに位置するコアキャッチャ上での発熱が強く、かつ二基目に貫通型DHXを起動する条件下において、この一時的な温度上昇は大きくなることが確認された。

In sodium-cooled fast reactors (SFRs), optimizing the design and operate decay heat removal systems (DHRSs) is important for safety enhancement against severe accidents. Thus, it is required to evaluate the cooling capability of DHRSs including the natural circulation behavior inside the reactor vessel during heat-removal phase that the fuel debris relocated in the reactor vessel is cooled by DHRSs. In this study, the experiments which simultaneously operations of the dipped-type DHX and the penetrated-type DHX were conducted to investigate the effect of operating multiple decay heat removal system on the natural circulation behavior in the reactor vessel. After achieving the stable conditions by operating the dipped-type DHX or the penetrated-type DHX, the other DHX was operated and the transient behavior was clarified by the temperature measurements. The clear temperature rise in the reactor vessel was confirmed by operating the penetrated-type DHX as second DHX operation under the condition of the dipped-type DHX operation at the beginning and the high heater power of fuel debris on the core catcher. Therefore, it was confirmed that the inhibition of the cooling for the decay heat occurred by operating multiple DHXs.