Experimental investigation on flashing-induced flow instability in a natural circulation scaled-down test facility

Abstract

With the deployment of nuclear technology and market demand, Small Modular Reactor (SMR) attracts a lot of attention of researchers and engineers which also was deeply studied and close to the wide application. The NuScale reactor is one of typical PWR-type SMRs which adopts the natural circulation system. The natural circulation is the main cooling method in the NuScale reactor which can simplify the nuclear reactor system. In this experimental investigation, a natural circulation test facility is scaled down from the prototype of NuScale reactor. This facility is operated at the low-pressure condition which is less than 0.5 MPa. The flow instability phenomenon was observed in the experiments which is regarded as the flashing-induced flow instability. The oscillation characteristics of the flashing-induced flow instability was observed and analyzed based on the results of flow rate, void fraction, and fluid temperature. The mechanism of the flashing-induced flow instability in the natural circulation system was analyzed based on the characteristics analysis. The effects of power and system pressure on the flashing-induced flow instability were also discussed. It is found that the flashing-induced flow instability can be suppressed by the increase of system pressure but induced by the increase of power.