Phase equilibria in nuclear fuel containing dysprosium

Mixtures of uranium and dysprosium oxide were sintered under controlled atmospheric conditions with the intention of developing condensed phases in equilibrium with gaseous atmospheres. The sintering was conducted in thermogravimetric apparatus to follow the course of compositional change associated with the loss or gain of oxygen. The resultant samples were sealed in evacuated silica capsules and studied by neutron diffraction at the Los Alamos Neutron Science Center. The patterns were analyzed by Rietveld refinement and used to further the development of a thermodynamic model for the phase equilibrium in the U-Dy-O system. The thermal expansion of the U-rich cubic solid solution was studied for samples prepared under both reducing and oxidizing conditions. The research is intended to contribute to an evolving understanding of Dy doped nuclear fuel used in the central element of a proposed new fuel bundle for use in the CANDU reactor. (author)