Analyses of ROSA-III break area spectrum experiments on a boiling water reactor loss-of-coolant accident

The ROSA-III program has conducted system effects tests on the thermal-hydraulic response of a boiling water reactor during a loss-of-coolant accident. The performance of the emergency core cooling systems was of particular interest. As part of this program, ten tests were conducted with (a) a simulated pipe rupture located at the recirculation pump suction line, (b) a spectrum of break area ranging from 0 to 200% of scaled pipe cross-sectional area, and (c) an unavailable high-pressure core spray (HPCS) system. In these tests the pressure vessel depressurized (a) due to the actuation of the automatic depressurization system for scaled break areas of <5%, (b) due to uncovery of the inlet of the broken recirculation pump suction line for scaled break areas of >50%, and (c) due to both for the intermediate break areas between 5 and 50%. Vessel depressurization enabled the injection of emergency core coolant from the low-pressure core spray and low-pressure coolant injection system and thus led to safe recovery without HPCS. The behaviors of the vessel pressure, core mixture level, and core temperatures were fairly well reproduced by the THYDE-B1 code, based on simplified lumpedparameter models for the wide spectrum of break areas investigated