INTERDIFFUSION BETWEEN U-ZR FUEL AND SELECTED FE-NI-CR ALLOYS

As part of studies relevant to fuel-cladding compatibility in the Inte gral Fast Reactors, isothermal interdiffusion experiments were carried out at 700-degrees-C with solid-solid diffusion couples assembled wit h a U-23 at% Zr alloy fuel and a series of cladding alloys of selected compositions in the Fe-Ni-Cr system. Besides pure Fe and pure Ni, the alloys included binary Fe-20.1Cr, Ni-16.4Cr, and Fe-10.1Ni and a tern ary Fe-16.4Ni-9.4Cr alloys (composition in at%). The diffusion structu res developed in the various couples were examined metallographically and by SEM-EDS analysis. The development of diffusion layers and their variation with compositional changes of the cladding alloys are discu ssed in the light of phase diagrams, intermetallic formation, the rela tive diffusion behavior of the various elements and the experimental d iffusion paths. From the composition profiles, average effective inter diffusion coefficients are determined for specific regions in the diff usion structures of selected diffusion couples. Intrinsic diffusion co efficients are also calculated at the composition of a marker plane in a (U,Zr)Ni2 phase layer.