The Thermionic Space Nuclear System Design and Technology Demonstration (TI‐SNPS) program requires a low‐risk, compact space nuclear power with a 5‐ to 40‐kWe scalability, high conversion efficiency and the potential for long life. The 40‐kWe S‐PRIME system uses conventional materials in a known operating environment and the multicell thermionic fuel element (TFE) technology database to produce a low‐risk approach to meeting the TI‐SNPS flight system requirements. This design approach limits the risks to four key areas: TFE performance and lifetime, TFE testability demonstration, hydrogen control, and radiator heat pipe performance. These areas require critical component testing reduce risks within the development program (Millset al.1993). A TFE testability critical component demonstration was one of the six demonstrations scheduled in the S‐PRIME Phase I Program. Multicell TFE testing techniques were pioneered in the countries of the former Soviet Union. The Institute of Physics and Power Engineering (IPPE) in Obninsk, Russia, a key S‐PRIME subcontractor, was tasked with reviewing this database and recommending the best technical approach for acceptance testing individual S‐PRIME TFEs and a network of TFEs in a reactor core assembly. IPPE developed (PPTE). Using the PPTF as a starting point, a 10‐step process is defined for acceptance testing the overall S‐PRIME power system, starting from the manufacturing process line for the individual TFEs to a final assembly and shipment of the power system to the launch site and its integration/checkout with the payload. © 1995American Institute of Physics