Studies on fuel-cladding chemical interaction between U−10 wt%Zr alloy and T91 steel

Abstract

The chemical interaction of U−Zr based fast reactor fuel with T91 grade steel cladding was investigated by employing DTA (differential thermal analysis), diffusion couple experiment and SEM/EDS, SEM/EBSD analyses. The DTA results revealed a strong exothermic reaction just below the solidus temperature of the U−Zr alloy. The eutectic liquefaction temperature between U−Zr alloy and T91 steel was found to be at 995 K. The interdiffusion between U–10Zr and T91 resulted in the formation of UFe2-type phase, a Zr-rich layer and a Zr-depleted layer at the interface. The growth kinetics of the reaction zone was also determined using the total width of UFe2 and Zr-rich reaction layers. The activation energy for the reaction was found to be 170 kJ mol−1. The Zr-rich layer at the interface acts as diffusion barrier which enhances the fuel-cladding chemical compatibility at reactor operating temperature. However, the U−Zr fuel is no more compatible with the cladding above the eutectic liquefaction temperature (995 K).