Effect of temperature on hardness of binary U–15%Pu alloy and T91 cladding

► Hardness–temperature plot of T91 alloy showed a transition at 778K. ► Hardness–temperature plot of α phase of U–15%Pu showed a transition at 408K. ► β Phase of U–15%Pu alloy showed a discontinuity in hardness data above 828K. ► γ Phase region of U–15%Pu was found to be very soft. ► At reactor operating temperatures, U–15%Pu fuel is softer than T91 cladding. The high temperature hardness behaviour of U–15%Pu and T91 cladding was studied with the help of a hot hardness tester. The hardness versus temperature plot for the T91 alloy consists of two straight lines with different slopes intersecting at 778K. The hot hardness data of orthorhombic α phase of U–15%Pu showed a transition at around 408K. The appearance of the tetragonal β-phase showed a sudden increase in the hardness above 828K. γ-Phase of U–15%Pu was found to very soft. Since U–15%Pu fuel is softer than the T91 cladding above 473K, the probability of the clad damage by the fuel due to its interaction with the cladding is very less.