PWR Small Break Loss-of-Coolant-Accident Experiment at ROSA-V/LSTF with a Combination of Secondary-Side Depressurization and Gravity-Driven Safety Injection.

Abstract

Investigation of thermal-hydraulic phenomena under natural circulation conditions at low pressures is important for development of a next-generation PWR relying on a secondary depressurization system (SDS) and gravity-driven safety injection system (GDIS) for long-term core cooling. Such phenomena have not been sufficiently investigated so far since they do not have significant importance in the safety analysis for the conventional PWRs. A loss-of-coolant accident test was conducted at the ROSA-V/LSTF, a large scale PWR simulator, using the SDS, GDIS and a flashing-driven safety injection system (FDIS) which is a newly proposed safety system in this study. The FDIS, unlike the conventional accumulator injection system, does not have a potential to bring noncondensable gas into the primary system and thus is advantageous for those reactor designs which rely on the SDS. From analyses of the test results, the effectiveness of the combined use of the SDS and GDIS on the long-term core cooling was confirmed, important thermal-hydraulic phenomena and characteristics of the FDIS were clarified, and the problems of the RELAP5/MOD3 code to predict low pressure behavior were identified.