[en] At present, that portion of the nuclear fuel cycle involving reprocessing, waste management, and mixed-oxide fuel fabrication is in an unsettled state. Government regulatory requirements with respect to all aspects of the back end of the fuel cycle are still being formulated, and there is little positive experience on the operation of commercial reprocessing or mixed-oxide fabrication plants. In view of this unsettled situation, it will be difficult to meet the reprocessing and mixed-oxide fabrication needs of the next decade in the pattern previously anticipated. The costs in the back end of the fuel cycle are much higher than had been anticipated several years ago, a situation similar to that of almost all large endeavors in this country. On the other hand, the added costs are small relative to total power costs and do not affect the economic advantage of nuclear power as compared to other power sources. A rough economic analysis indicates that the question for the back end of the fuel cycle has changed from one of optimizing profitability to one of determining the most economic disposition of spent fuel. Long-term spent fuel storage is a practical and economically acceptable way to provide time for determining a sound course of action for the back end of the fuel cycle. Indeed, if one could count on a breeder economy before the end of the century, one possible course of action is to store light-water fuel until the plutonium can be used in breeders. However, for philosophical as well as practical reasons, it is important that the uncertainties in the course of action should be resolved as quickly as possible. Long-term storage should not be an excuse to delay resolution of the basic questions. (U.S.)