Study on thermal stratification in a compact reactor vessel of advanced sodium cooled reactor

Kamide, Hideki ; Ogawa, Hiroshi; Kimura, Nobuyuki; Hayashi, Kenji; Tobita, Akira

Thermal stratification after a scram is one of main thermal loads of a reactor vessel in sodium cooled reactor. Water experiments using an 1/10th scaled model were carried out for an advanced loop type sodium cooled reactor, which was designed by FBR Feasibility Study in Japan. The reactor vessel is highly compact and has an upper inner structure (UIS), which consists of perforated baffle plates and has a slit in radial direction for fuel handling. This slit makes high velocity flow in the UIS. Steep temperature distribution across the stratification interface and temperature fluctuations were found near the UIS slit in the experiment. It was revealed that they were resulted from the impingement of the jet through the slit at the interface. Dominant period of temperature fluctuations at stratification interface was influenced by the jet velocity through the UIS slit and also temperature difference across the interface.