Title

The Synthesis and Sintering of Nitrides of Uranium and Dysprosium

Publication Date

12-2008

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Materials Science and Engineering

Department

Materials Science and Engineering

Major Advisor

Darryl P. Butt

Abstract

The future of nuclear energy in the U.S. and its expansion worldwide depends greatly on our ability to reduce the levels of high level waste to minimal levels, while maintaining proliferation resistance. Implicit in the so-called advanced fuel cycle is the need for higher levels of fuel burn-up and consequential use of complex nuclear fuels comprised of fissle materials such as Pu, Am, Np, and Cm. Advanced nitride fuels comprised ternary and quaternary mixtures of uranium and these actinides have been considered for applications in advanced power plants, but there remain many processing challenges as well as necessary qualification testing. Nitrides are desirable candidates for advanced nuclear fuel applications due to their high actinide density and thermal conductivity as well as their low coefficient of thermal expansion. In the present study, nitrides of uranium and dysprosium were synthesized using both traditional and novel synthesis techniques prior to mixing and sintering. Phase pure uranium nitride was synthesized using three different methods; reactive milling uranium metal in nitrogen at room temperature, hydriding uranium metal prior to nitridation at 320°C, and carbothermically reducing UO2 prior to nitridation at 1400°C. Phase pure dysprosium nitride was synthesized by four different methods, including; reactive milling dysprosium metal in nitrogen at room temperature, direct nitridation at 1300°C, the simultaneous hydride and nitride formation in a nitrogen hydrogen mixed gas prior to full conversion to dysprosium nitride in pure nitrogen, and a carbothermic reduction of dysproia prior to nitridation at 1500°C. The powders were characterized for purity using x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS). Furthermore, the powders were characterized for size and morphology using laser scattering techniques and scanning electron microscopy (SEM). Following the successful synthesis of UN and DyN powders, (Ux, Dyl-x)N (x = 1 to 0.7) solid solutions were systematically mixed and sintered. The mixtures were dry milled for 24 hours prior to pressing at 420 MPa in a 0.2500 inch pellet die. The effects of temperature, time, and atmosphere on the final sintered densities and weight losses of the compacts were assessed.

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