Water experiments on thermal striping in reactor vessel of Japan Sodium-cooled fast reactor; Countermeasures for control rods and radial blanket assemblies

Kobayashi, Jun ; Kimura, Nobuyuki; Tobita, Akira; Kamide, Hideki ; Watanabe, Osamu*; Oyama, Kazuhiro*

Design study of an advanced loop-type sodium-cooled fast reactor, JSFR, has been carried out in a frame work of Fast Reactor Cycle Technology Development Project (FaCT) in Japan. As the temperature differences among the control rod channels, blanket assemblies and the core fuel assemblies are 100C centigrade in the maximum, temperature fluctuation due to the fluid mixing at the core outlet may cause high cycle thermal fatigue at the bottom of Upper Internal Structure (UIS). In this investigation, a water experiment was conducted using a 1/3 scale 60 sector model of the core and reactor upper plenum. Characteristics of temperature fluctuations near the cold fluid outlets were obtained and it was confirmed that several countermeasures can reduce temperature fluctuations at the bottom of UIS.