ナトリウム冷却高速炉の原子炉容器底部へのデブリの堆積による原子炉容器の変形に関する予備解析

Preliminary deformation analysis of the reactor vessel due to core debris accumulation onto the reactor vessel bottom for Sodium-Cooled Fast Reactor

小野田 雄一 ; 山野 秀将   

Onoda, Yuichi; Yamano, Hidemasa

原子炉容器内におけるデブリの安定冷却に関する幅広い事象スペクトルの検討に資することを目的として、原子炉容器底部に堆積するデブリによる原子炉容器の変形挙動について破損に至るまでの解析を有限要素法を用いて実施した。崩壊熱を考慮した過渡熱伝達解析を行うとともに、これにより得られる温度分布を用いて原子炉容器およびその外側に設置されるガードベッセルの構造応答解析を行った。原子炉容器の温度が約1,100Cになると荷重を支えることができずに急激に変形が進行し、原子炉容器が破損に至るとの結果を得た。

In Japan, sodium-cooled fast reactor (SFR) design takes In-Vessel Retention (IVR) strategy to stable cooling the damaged core material in the reactor vessel against severe accidents by various design measures. Although a possibility to fail IVR is extremely unlikely, a probabilistic risk assessment study needs a wide variety of scenarios including the IVR failure. Therefore, in order to study of a wide range of event spectra related to stable cooling of debris in the reactor vessel, the deformation and failure behavior of the reactor vessel due to the debris deposited on the bottom of the reactor vessel are investigated in this study using the FINAS-STAR. Structures including reactor vessel and guard vessel which locate below the core catcher at the bottom of the reactor vessel are modeled. The amount of debris falling to the bottom of the reactor vessel is tentatively determined to 30% of the core inventory. The analyses are conducted in two cases of power density with the aim of establishing conditions for failure the bottom of the reactor vessel. Reactor vessel deforms significantly when the temperature reaches about 1100C and the reactor vessel failed in both calculation cases in the analysis of current conditions.