LOCA Analysis of Super LWR

Abstract

LOCA analysis of the supercritical-pressure light water cooled thermal reactor with downward-flow water rods (called Super LWR) are carried out to clarify its characteristics. 1–100% hot/cold leg breaks are analyzed. At the cold-leg large break, excessive core heat-up is mitigated by the automatic depressurization system (ADS) during blowdown because reactor depressurization induces core coolant flow. The coolant inventory in the top dome and the water rods is effectively used for core cooling. After blowdown, the core is slowly re-flooded by the low-pressure ECCS like PWR. The highest cladding temperature of the large LOCA is lower than the criterion (1,260°C) by about 430°C which appears during the reflooding phase. Small break of the cold-leg gives the higher cladding temperatures than that of the large break because the ADS are not actuated in the analysis. The highest cladding temperature is lower than the criterion by about 260°C. If the ADS actuation is assumed by the “drywell pressure high” signal, the cladding temperature is lower. The hot-leg break is less severe than the cold-leg break because it increases the core coolant flow rate and forced flooding is expected after blowdown.