[en] The purpose of this report is to define a preliminary thorium fuel cycle to serve as a common basis for beginning development work on October 1, 1977, at participating ERDA laboratories, universities, and commercial facilities. Characteristics of the reference fuel cycle for the Thorium Fuel Cycle Technology (TFCT) program are: fissile uranium will be denatured by mixing with ²³⁸U; chemical processing plant design will be based on the assumption that plants are located in secure areas; plutonium will be recycled within these secure areas; thorium will be recycled with recovered uranium and plutonium; the head end of the chemical processing plant will handle a variety of core and blanket fuel assembly designs for light water reactors and heavy water reactors; the fuel form will be a homogeneous mixture of uranium and thorium oxide powders pressed into pellets; fuel cladding will be Zircaloy; and MgO will be added to the fuel to improve the thorium dissolving characteristics