BWR main steam line break LOCA tests RUNs 951, 954 and 956 at ROSA-III

This report presents the experimental results of RUNs 951, 954 and 956 in ROSA-III program, which are medium or small main steam line break LOCA tests with assumption of HPCS failure. The ROSA-III test facility simulates a BWR system with volume scale of 1/424 and has four half-length electrically heated fuel bundles, two active recirculation loops, four types of ECCS's, and steam and feedwater systems. Effects of break area on the depressurization rate, water level and void fraction of the downcomer fluid, and core cooling phenomena were investigated by comparing the present test results with those of RUN 953, a 100 % main steam line break test. Namely, (1) the maximum void fraction in the downcomer, which affected the water level swelling, was found to be closely related with the total steam flow area of the main steam line. (2) The ADS actuation affected significantly the system responses in the small steam line break LOCAs. (3) The PCT was higher in a larger steam line break LOCA. (author)