Reactions of uranium-plutonium alloys with iron

In metallic U-Pu-Zr fuel for fast reactors, metallurgical reactions occur b etween the fuel alloy and the stainless steel cladding, and a liquid phase may be formed in the reaction zone at a higher temperature. In order to cla rify the condition for liquefaction at the fuel-cladding interface, the rea ctions of U-Pu alloys with Fe have been examined at 923 and 943 K. The test results confirmed that the liquid phase is not formed at 923 K in any regi on of the reaction zone when the maximum Pu content in the (U,Pu)(6)Fe phas e is less than the Pu solubility limit in this phase. Comparison of the pre sent test results with the liquefaction data from the various tests on meta llic fuel-cladding compatibility suggested that the liquefaction condition is independent of the Zr content in the fuel alloy and can be expressed as a function of the atom fraction ratio of Pu/(U+Pu) in the fuel alloy and th e reaction temperature. At 923 K, liquefaction will occur when the Pu/(U+Pu ) ratio is larger than 0.25.