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

Onoda, Yuichi ; Yamano, Hidemasa   

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.