Professor Emeritus Dr. Rock Mackie, Medical Physics; Dr. Kevin Eliceiri, Morgridge Medical Engineering and University of Wisconsin-Madison; Professor Dr. Michael Corradini, Engineering Physics, and Dr. Gary Stange collaboratively developed a crystalline-fuel reactor system with an annular fuel design for improved efficiency of medical isotope production with a nuclear reactor. Molybdenum-99 (99Mo) is required to produce technetium-99, used in more than 30 million medical imaging procedures yearly. The US accounts for half of the worldwide demand of molybdenum-99 with no domestic production, creating a supply shortage risk from unplanned shutdowns of foreign isotope production reactors. Crystalline fuel is used for more efficient fuel recycling: the temperature of dissolved spent fuel can be lowered to the point that uranium forms a solid crystal, leaving waste products in the liquid to be separated. Crystalline fuel also has a low melting temperature (61°C), and our critical reactor system was developed with annular pin geometry to improve heat transfer and prevent melting. Our experimental fuel analysis device measures thermal conductivity of the crystalline fuel material to ensure no melting occurs. It was designed, fabricated, and assembled in the Medical Engineering Fab Lab at the Morgridge Institute for Research with traditionally-machined and 3D-printed components.