Interaction Behavior between Binary Lanthanide Alloy and HT9

When the U in metal fuel and Fe in fuel cladding come into contact at temperatures above 780 .deg. C, the resulting eutectic phenomenon causes mutual fusion, and when Pu is added, the eutectic temperature is lowered to 650 .deg. C (Fuel Cladding Chemical Interaction, FCCI). Among the nuclear fission products included in the light water reactor fuel rod, a small amount of rare earth metals exist, such as Ce, La, Pr, Nd, Sm, and so on. These elements are initially added to the SFR metallic fuel through pyroprocessing, to about 1 wt%. Also, as SFR operation continues, additional amounts of rare earth elements are newly produced as a fission product. These elements are moved by the temperature gradient and accumulate at the surface of the fuel rod, where these rare earth elements contribute negative effects, such as decreasing the temperature at which the eutectic phenomenon occurs and increasing the reaction layer. In this study, the effects of Ce and Nd, which dominantly influence FCCI, were evaluated in order to qualitatively analyze the effect of each element on such interactions. In order to conduct experiments, a binary model alloy was fabricated by changing Ce and Nd content, and after conducting diffusion couple tests with the SFR cladding tube material HT9, the effect of elemental content was assessed through microstructure analysis. The result showed that Ce and Nd reacted with the Fe of the cladding material to form an interaction layer, and synergetic phenomena significantly affecting the interaction layer thickness was observed when their composition reached nearly 1:1, which is due to the overlapping reaction mechanisms between Ce and Nd with Fe. Further tests regarding synergistic effect on binary lanthanide elements (Ce, Nd, Pr, La, Sm) will be conducted by fixing element contents, 1:1.