Abstract
During the boration process, the large volume water of the Volume Control Tank (VCT) in the Reactor Coolant System (RCS) is disadvantaged to the mixing between the incoming solution and the initial water. When the Richardson Number of the inlet buoyant jet is high enough, the density stratification would be formed. And the mixing inside the VCT would be weakened. The poor mixing would lead to the instability of reactivity and overshoot or undershoot of the reactor power.
In this paper, a series of experiments with different concentrations, flow rates, and nozzle diameters were carried out to investigate the dynamic characteristics of the outlet boron concentration of the VCT.
In our work, the time required for the outlet concentration to reach 63.2% is defined as the characteristic time. And an experimental correlation of the characteristic time is proposed with a maximum error of 16.95%.
The results show that with the increase of the flow rate, the characteristic time decrease. And a higher concentration is beneficial to decrease the characteristic time. As for nozzle diameter, a smaller diameter causes a decrease of the characteristic time, but the effect is not significant.
Furthermore, it is worth noting that in some conditions, the outlet concentrations finally increase slower compared to that of the complete mixing condition. Though the above conditions decrease the characteristic time. The reason might be that there is a dead zone in the tank.
