ISOTHERMAL DIFFUSION IN URANIUM-PLUTONIUM-ZIRCONIUM ALLOYS

Isothermal diffusion couple experiments were performed at 1023 K to in vestigate diffusion phenomena in body-centered cubic U-Pu-Zr alloys. T he U-Pu-Zr alloys covered the uranium-rich comer of the ternary phase diagram with plutonium concentrations up to 27 at.% and zirconium conc entrations up to 20 at.%, Ternary interdiffusion coefficients were cal culated at the common composition between two couples with intersectin g diffusion paths. The cross interdiffusion coefficient for zirconium ((D) over tilde(ZrPu)(U)) is negative and has a magnitude twice that o f the main coefficient ((D) over tilde(ZrZr)(U)). In contrast, (D) ove r tilde(PuZr)(U) is negligible compared with (D) over tilde(PuPu)(U). (D) over tilde(PuPu)(U) is an order of magnitude greater than (D) over tilde(ZrZr)(U). Average effective interdiffusion coefficients were de termined for all components over concentration ranges on the two sides of the Matano plane as well as for the entire diffusion zone of the c ouples. In general, these coefficients increase with increasing pluton ium concentration and decrease with increasing zirconium concentration .