Reactions between U-Pu-Zr alloys and Fe at 923 K

In metallic U-Pu-Zr fuel, metallurgical reactions occur between the fuel sl ug and the cladding, and a phase of which the melting point is relatively l ow is formed in the reaction zone. If a liquid phase is Formed. it can degr ade cladding integrity. The potential for liquid phase formation near the c ladding, therefore, should he excluded during normal reactor operation. In order to clarify the mechanism of liquefaction, the authors have conducted diffusion experiments at 923K using two couples: U-13at%Pu-22a%Zr/Fe and U- 22at%Pu-22 at%Zr/Fe, and examined the influence of the Pu content in the fu el alloy on the phases formed in the reaction zones. The liquid phase has b een observed in the U-22 at%Pu-22at%Zr/Fe couple. An assessment of the diff usion paths for these couples has indicated that the Pu content in the (U, Pu)(6)Fe-type phase in the reaction zone is a crucial factor in determining the conditions that lead to liquefaction. The Pu content in the (U, Pu)(6) Fe-type phase increases with that in the initial U-Pu-Zr alloy. The fuel de sign specifications to exclude the potential for liquefaction will be clari fied by further examination of the Pu content in the (U, Pu)(6)Fe-type phas e for various U-Pu-Zr/Fe couples annealed at different temperatures.