General design criteria and descriptions of the Waste Solidification Engineering Prototypes equipment are discussed. The WSEP is a developmental facility for solidifying highly radioactive liquid wastes from reprocessing of power reactor fuels by the pot, spray, and phosphate glass processes. Design criteria are based upon providing a developmental facility with a high degree of flexibility and integrity for demonstrations of various waste solidification processes and equipment with fully radioactive materials. Special features of the equipment for process and mechanical functions to be performed during the demonstrations are presented. Process functions include overall flowsheet requirements, process control features, process effluent treatment and control, and special features of process equipment. Mechanical functions include remote handling and transfer of material and equipment, and storage and testing of containers full of soldified waste. Equipment performance during nonradioactive shakedown tests, and the process safety review are summarized. Equipment performance has been good, and the first radioactive run was made in the WSEP in November 1966.