The establishment of nuclear fuel requirements and their efficient utilization requires a detailed knowledge of some aspects of fuel dynamics and processing during the reactor lifetime. It is shown here that the use of the fuel stockpile inventory concept can serve effectively for this fuel management purpose. The temporal variation of the fissile fuel doubling time as well as non equilibrium core conditions are among the characteristics which thus become more evident. These characteristics—rather than a single figure-of-merit—clearly provide an improved description of the expansion capacity and/or fuel requirements of a nuclear reactor energy system.