Redistribution behavior of various constituents in U-Pu-Zr alloy and U-Pu-Zr alloy containing minor actinides and rare earths in a temperature gradient

Abstract

U-Pu-Zr based metallic fuel is one of the likely possible candidate to transmute minor actinides, such as Np, Am and Cm (MA). MA can be recovered from the high-level waste by pyroprocess, where the presence of rare earths (RE) will not be avoided. One of the most important phenomena observed on U-Pu-Zr metallic fuel type is the redistribution of the elements in a temperature gradient. In order to evaluate the redistribution, especially of MA and RE, three samples of one U-Pu-Zr alloy and two U-Pu-Zr-MA-RE alloys were heated in a temperature gradient and were analyzed by metallography, α-autoradiography and electron microprobe. The results indicated that Zr migrated to the colder region in both kinds of specimens, and that in U-Pu-Zr-MA-RE, Am and RE did not significantly move at temperatures below 1020 K, whereas Pu and Np concentrations slightly increased in the region around 900 K. By contrast, a significant depletion of Am and RE was observed in the hotter region above 970 K, while they migrated to the colder region of the sample, when the highest temperature in U-Pu-Zr-MA-RE was at above 1270 K. The transformation of the γ phase into a Zr-rich and a U-rich phases was observed in the hotter region, probably corresponding to the γ 1-γ 2 miscibility gap region in the U-Zr system.