Section 161(v) of the Atomic Energy Act of 1954 authorizes the Department of Energy (DOE) to offer its services, for a fee, to convert natural uranium into the enriched uranium used for fuel in commercial reactors, and provides that DOE "shall" restrict its enrichment of foreign-source uranium intended for use in domestic facilities "to the extent necessary to assure the maintenance of a viable domestic uranium industry." DOE has determined that the domestic uranium industry has not been "viable" since 1983, and that the imposition of restrictions on DOEs enrichment of foreign uranium would not assure viability. Respondent domestic uranium mining and milling companies filed suit against petitioners (DOE and some of its officers and employees) in Federal District Court, alleging that DOEs failure to impose restrictions on the enrichment of foreign uranium for use in domestic facilities constituted a violation of 161(v). Respondents moved for summary judgment based on this claim, arguing that two facts - that the domestic industry was not via