Abstract
Small miniature lead-cooled fast reactors use assemblies with hexagonal cross-sections as their fuel assemblies. There are gaps of a few millimeters between the two assemblies. Under normal operating conditions, the flow and heat transfer are usually ignored in these gaps. However, the heat transfer capability of the core by-pass narrow slit flow cannot be ignored under accident conditions. Although lead-cooled fast reactors have received less research, this narrow slit flow has been confirmed in studies using sodium-cooled fast reactors. As a result, its heat transfer capacity needs to be determined to assure core safety in the event of an accident. In order to simulate the narrow-slit flow in the core of a small miniature lead-cooled fast reactor and study the flow state, temperature, and velocity distribution of the narrow-slit flow in the core within the natural circulation flow range, a core model with only interstitial channels are constructed, and a hole is cut in the bottom of the enclosure. According to the results, the core exhibits clear temperature stratification in the height direction and a significant temperature gradient at 4% power; the average flow velocity inside the narrow slit declines as power increases, and when the core power is below 10%, fluid inside the narrow slit gap contributes more to the core cooling capacity; and a clear vortex or transverse flow appears inside the narrow slit.
