Multicomponent Alloys Based on U-Pu as a Fast Reactor Fuel

The authors study multicomponent alloys based on U-Pu, to which Mo, Nb, Zr and Ru are added. From the results of microstructure, X-ray and differential thermal analyses it is established that the added elements vary in their ability to stabilize the γ phase: molybdenum has the strongest stabilizing effect, followed by ruthenium, niobium and zirconium. Various of the alloys' physical constants are determined: melting point, thermal conductivity, change in volume at the moment of phase transition, specific weight and coefficient of linear expansion. The short-term rigidity at high temperatures of some of the alloys is studied by the bending method. It is found that the high-temperature rigidity of the alloys is increased most by molybdenum. Ruthenium also produces a significant increase in high-temperature rigidity, but less than molybdenum. The high temperature rigidity of an alloy depends to a great extent on its plutonium content; in the case of a ternary U-Pu-Mo alloy containing 9 wt.% Mo, for example, the sag (for the same load and temperature) is 2.5 and 9.5 mm respectively for 15 wt.% Pu and 20 wt.% Pu. The high-temperature rigidity of a ternary U-Pu-Mo alloy containing 20 wt.% Pu and 9 wt.% Mo is of the same order as that of a U-Pu alloy containing 8.6 wt.% fissium. The stability of the γ phase in multicomponent alloys at 500°C was studied by microstructure analysis. A more accurate phase diagram for U-Pu alloys is obtained by the authors in the concentration range 0-50 wt.% uranium. The existence is established of an eutectoid horizontal at 430°C produced by three-phase equilibrium, ή(δ')-->δ+X'(δ). The extent of the eutectoid horizontal at 260°C is determined more accurately: it is found to extend to 5 wt.% uranium, and not to 4.2 wt.% as reported previously. (author)