Recently, most of the countries using nuclear power for electricity generation are working towards the safer and the more economical designs. In practice some typical nuclear steam supply system (NSSS) vendors are developing evolutionary reactors or passive type reactors based on current technologies. One of the most important features of these advanced reactors is system simplicity. In this study, a model has been presented to quantitatively evaluate system simplification. Design enhancements in simplicity of the chemical and volume control system (CVCS) of the ABB-CE System 80+ and the Korean standardized nuclear power plant (KSNPP) have been evaluated using the presented model. The quantification model is based on the informational entropy concept and system availability analysis. The quantification results indicate that the simplicity of the CVCS is highly dependent on the type and the number of charging pumps. Also, it is found that higher redundancy does not always result in higher availability. Finally, it is stated that the informational entropy concept and the system availability analysis can be a valuable tool for the quantitative evaluation of system simplification.