Water experiments on thermal striping at upper internal structure of Japan sodium-cooled fast reactor

JAEA has been conducting a design study for an advanced large-scale sodium-cooled fast reactor (SFR). Hot sodium from the fuel subassembly can mix with the cold sodium from the control rod (CR) channel and blanket assemblies at the bottom up Upper Internal Structure (UIS). Temperature fluctuation due to the fluid mixing at the core outlet may cause high cycle thermal fatigue at the bottom of UIS. JAEA had performed a water experiment to examine countermeasures for the significant temperature fluctuation generated at the bottom of SFRs UIS. A water experiment was conducted using a 1/3 scale 60deg-sector model of the reactor core and upper plenum. The temperature fluctuations near the cold fluid outlet were determined, a several countermeasures were tested. It was confirmed that these countermeasures could reduce the temperature fluctuations at the bottom of the UIS. (author)