Regulating boron concentration is one of the important ways to control reactivity in pressurized water reactor (PWR) nuclear power plants. When the unit is shut down, concentrated boric acid needs to be added to the Reactor Coolant System (RCS) through the Chemical and Volume Control System (CVCS) to increase the bulk boron concentration of RCS. This process is called boration operation. The volume control tank (VCT) is the main equipment of CVCS. Its internal mixing is very weak. In some cases, concentration stratification is even present in VCT. This phenomenon causes the injected concentrated boric acid to be retained in the VCT. As a result, the boron concentration of RCS cannot be stabilized quickly, affecting the reactor's safe operation. This paper focuses on the dynamic characteristics of VCT outlet concentration during boration operation. The effects of flow rate, concentration difference, and inlet nozzle size of VCT on the dynamic characteristics of outlet concentration are studied in a wide range of parameters. As the flow increases, the response time is shortened. When the Richardson number is less than 0.067, the response time is positively correlated with the concentration difference and the nozzle size. When the Richardson number exceeds 0.067, the response time is negatively correlated with the concentration difference and the nozzle size. In addition, the experimental correlation for predicting response time is proposed (error < 20%). This study provides an essential theoretical basis for the VCT design of HPR-1000 and other similar units.