This paper describes the results obtained from a simulation study of electric utility system expansion with various amnounts of nuclear generation in large units. Estimates of capital costs, fuel costs, and operation and maintenance costs are used for closed-cycle water plants from 600 to 1,000 mw (megawatts). The economic applications of specefic plants are studied in terms of present worth of all future revenue requirements. Additional studies investigate the effect of varying nuclear unit availability, fossil-fuel escalation assumptions, and nuclear fuel prices.