This book describes the fast reactor (FR), a type of new reactor for nuclear plants, currently under research and development. The book targets young researchers and engineers who will be charged with commercializing this new type of reactor to lead to the development of new components and systems for improved plant reliability and economy. This volume also helps readers to understand the methods of integrating the power plant in its entirety, from the reactor core to all of the various systems and components, and teaches the way of thinking that forms the background of these methods. This background includes the various organizational and management issues that are encountered as projects move forward and will be explored in great detail based on actual design and construction experience with Japan prototype FR, Monju.