Experimental study on prevention of high cycle thermal fatigue in a compact reactor vessel of advanced sodium cooled reactor; Thermal striping phenomena at bottom of upper internal structure

Kobayashi, Jun ; Kimura, Nobuyuki; Tobita, Akira; Kamide, Hideki 

As the temperatures difference between the control rod channels and the core fuel subassemblies is around 100 C centigrade, 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 JSFR. Then, a water experiment was conducted using an 1/3 scale 60 sector model. As a result, thermal striping phenomena in the region between the fuel subassembly outlet and the bottom of the UIS were grasped. The modified geometry of the UIS bottom and the handling head of the primary CR channel was created so as to suppress the cold jets from the CR channels. The comparison of measured temperature fluctuations around the CR channels revealed that the modified geometry was effective to decrease the temperature fluctuation intensity and amplitude in the sensitive frequency band to the stress conversion.