Abstract
Experimental results of the ROSA-II hot leg break tests with ECCS injection were compared with these of cold leg break tests. Adequacy of the RELAP-3 prediction of extremely severe break configuration for core cooling during blowdown was confirmed by parameteric tests on the conditions. The major conclusions are as follows:(1) In a large break of hot leg piping, downward core flow at the early stage of blowdown process is weak and almost stagnant. Therefore fuel temperature begins to rise at early time after break due to exposure to steam void under free water level.(2) Since upward steam flow in downcomer is weak, accumulator injection results in remarkable water accumulation in pressure vessel. Therefore core cooling during reflooding process is better. Injection location of low pressure coolant injection system is less sensitive to core cooling.
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