The back end of the nuclear fuel cycle has been analyzed under current conditions in the United States, taking into consideration the framework defined by the Nuclear Waste Policy Act of 1982 and its amendments. The different steps of the back end of the fuel cycle are studied and different alternatives are compared under technical and economic criteria. Several technical issues have been analyzed for their impact on the economics of the fuel cycle. The bases for the analysis are explained, and the results for a once-through cycle are presented. The results show that a repository in tuff represents the minimum cost situation. The economic model appears very sensitive to several parameters, in particular the period of retrievability and the storage costs.