This work is concerned with modeling and digitally simulating the subsystems of a nuclear power plant. The subsystems that are modeled are the reactor, steam generators, pressurizer, boron addition system, feedwater system, steam lines, and turbine. The objective of this work is to develop models that will adequately predict the transient performance of the plant for large power excursions. Characteristics of each subsystem that are deemed important in determining the transient response of the overall plant are modeled. Simulations of the individual subsystems are presented. How the various subsystems should be interconnected to form the overall model is discussed. / Ph. D.