In this study, an integrated boration and dilution (INBAD) model is proposed to predict the required makeup flowrate for RCS boron concentration change and to analyze the boron concentration behavior at each subsystem within the RCS including CVCS during boration and dilution operation. The INBAD model is constructed by integrating an existing neutronic code and a boration and dilution model. The boration and dilution model has been developed for our specific purpose using the one-cell model and multi-cell model. In addition, in order to assess the boron concentration behavior more realistically, two important features such as variable pressurizer heater output and optional makeup mode (either direct or indirect injection) are implemented in this model. In order to demonstrate the usefulness of this model, the boron concentration behavior analysis at each subsystem were performed for both direct and indirect injection mode using YGN 3 and 4 design data. Also, the effect of pressurizer heater output on the primary loop boron concentration was investigated. The results showed that the boron concentration changes can be predicted accurately at each subsystem during boration and dilution operation.