Fabrication and Testing of Uranium Nitride Fuel for Space Power Reactors

Uranium nitride fuel was selected for previous space power reactors because of its attractive thermal and physical properties; however, all UN fabrication and testing activities were terminated over ten years ago. An accelerated irradiation test, SP-1, was designed to demonstrte the irradiation performance of Nb--1Zr clad UN fuel pins for the SP-100 program. A carbothermic-reduction/nitriding process was developed to synthesize UN powders. These powders were fabricated into fuel pellets by conventional cold-pressing and sintering. The pellets were loaded into Nb--1Zr cladding tubes, irradiated in a fast-test reactor, and destructively examined after 0.8 at.% burnup. Preliminary post-irradiation examination (PIE) results show that the fuel pins behaved as designed. Fuel swelling, fission-gas release, and microstructural data are presented, and suggestions to enhance the reliability of UN fuel pins are discussed. 21 ref.--AA