This chapter systematically introduces the application and development of exergoeconomic analysis methods in the thermodynamic systems of NPPs. The exergoeconomics combines thermodynamic analysis with economic principles to evaluate the economic efficiency of energy systems through the establishment of exergy cost equations (e.g., the relationship between fuel exergy and product exergy costs). It addresses optimization in NPP design, operational cost control, and feasibility assessments. Key discussions focus on exergy cost models for major equipment (e.g., reactors, heat exchangers, turbines), the balance between operational costs and exergy efficiency, and the economic criterion for improvement measures. Additionally, it introduces the principles of thermoeconomic isolation and quasi-isolation to decompose complex systems into subsystems for optimization, simplifying global design challenges, with the ultimate goal of minimizing total system costs.