This chapter focuses on the exergy analysis of NPP thermal systems. By integrating the First and Second Laws of Thermodynamics, this method evaluates energy transformations in terms of both quantity and quality, revealing work capacity loss caused by irreversible factors. Key equipment such as reactors, pumps, heat exchangers (e.g., steam generators, condensers), and turbine-generators are analyzed, with reactors identified as the largest contributor to exergy loss due to energy conversion inefficiencies and heat transfer temperature differences. Case studies comparing the Qinshan Phase I and Daya Bay plants highlight that traditional energy balance analyses overlook “quality-based energy loss,” which is the primary cause of inefficiency. The chapter concludes with exergy optimization strategies, emphasizing adjustments to feedwater temperature and condenser pressure to enhance system efficiency, while advocating for holistic optimization over localized improvements.