[en] The nuclear energy center (NEC) concept is an approach to siting wherein nuclear facilities would be clustered in and delimited to a relatively small number of locations throughout the United States. These designated centers would be concurrently developed to their full capability over several decades, at which time, they would be several times larger than the largest nuclear power stations in existence today. The centers would be permanently dedicated to nuclear operations including the future decommissioning of functionally obsolescent facilities as well as the commissioning of their replacements. The criteria for and characteristics of an acceptable nuclear energy system that could supply most of the U.S. energy requirements in the distant future are discussed. The time period is unspecified but occurs when fossil-fuel resources are depleted to such an extent that their use is economic only in special situations, and is not economic, in general, for use as fuel