DEVELOPMENT AND EVALUATION OF MIXED URANIUM-REFRACTORY CARBIDE/REFRACTORY CARBIDE CER-CER FUELS. IN THIS PROPOSAL, A NEW CARBIDE-BASED FUEL IS INTRODUCED WITH OUTSTANDING POTENTIAL TO ELIMINATE THE LOSS OF URANIUM, MINIMIZES THE LOSS OF URANIUM AND RETAINS FISSION PRODUCTS FOR MANY HOURS OF OPERATION IN HYDROGEN ENVIRONMENT AT TEMPERATURES IN EXCESS OF 3,200K. THE PROPOSED FUEL IS A CERAMIC-CERAMIC (CERCER) COMPOSITE OF MIXED URANIUM-REFRACTORY CARBIDES SUCH AS (U,ZR)C OR (U,ZR,NB)C IN A MATRIX OF REFRACTORY CARBIDES THAT MOSTLY INCLUDE TRANSITION METAL CARBIDES SUCH AS ZRC, NBC, TAC AND HFC. DUE TO ITS LOW NEUTRON ABSORPTION CROSS-SECTION, ZRC IS THE PRIMARY REFRACTORY CARBIDE OF CHOICE. REPLACING ZRC WITH HIGHER TEMPERATURE REFRACTORY CARBIDES SUCH AS TAC AND HFC COULD FURTHER IMPROVE THE HIGH TEMPERATURE PERFORMANCE OF CERCER FUELS. HOWEVER, HIGHER NEUTRON ABSORPTION CROSS-SECTION PENALTY FOR A TA AND HF COULD POTENTIALLY OFFSET THE PERFORMANCE ENHANCEMENT GAIN. DUE TO COMPLETE CONTAINMENT AND ENCAPSULATION OF MIXED URANIUM CARBIDE IN ZIRCONIUM CARBIDE MATRIX, THE PROPOSED CERCER FUEL COULD BE CONVENIENTLY FABRICATED TO DIFFERENT GEOMETRIAL SHAPES SUCH AS SOLID BLOCK PRISMATIC, TWISTED RIBBON, PEBBLES, WAFER OR SQUARE LATTICE HONEYCOMB. CONSIDERING THE OPERATIONAL PARAMETERS FOR THE NT/BP SYSTEMS, IT IS REASONABLE TO ARGUE THAT THE PROPOSED CERCER FUEL CONCEPT COULD SET THE PROPER MATERIAL PERFORMANCE LIMITS WHILE PROVIDING MORE FLEXIBILITY IN THE GEOMETRICAL DESIGN OF THE FUEL.