10 C.F.R. § 766.101
DOE shall use the records from the Toll Enrichment Services System (TESS) and other records maintained by the Oak Ridge Operations Office in order to determine the total SWUs purchased from DOE for all purposes. DOE shall use records from TESS, relevant records of domestic utilities, and such other information as DOE deems to be reliable and probative in determining the number of SWUs that were purchased by each domestic utility prior to October 24, 1992. A domestic utility shall be considered to have purchased a SWU from DOE if the SWU was produced by DOE but purchased by the domestic utility from another source. DOE shall consider a purchase to have occurred upon the delivery of a SWU to the domestic utility purchasing the SWU. A domestic utility shall not be considered to have purchased a SWU from DOE if the SWU was purchased by the domestic utility but subsequently sold to another source.
10 C.F.R. § 766.101