Reaction of lanthanide elements with Fe-Cr alloy

During steady-state irradiation of metal fuel in fast reactors, lanthanide fission products react with the Fe-base cladding and cause wastage of the cladding inner surface. In order to provide the basis of the cladding wastage modeling, the authors conducted isothermal annealing tests of diffusion couples consisting of Fe-12wt.%Cr alloy and lanthanide alloy, 13La-24Ce-12Pr-39Nd-12Sm (in wt.%), which simulates fission yield of lanthanide elements. In the temperature range of 773-923 K, Fe diffused into the lanthanide alloy side and formed Fe2RE precipitates, where RE stands for lanthanide element mixture. Cr did not migrate evidently. The lanthanide elements diffused into the Fe-Cr side and formed the distinct reaction zone. This reaction zone showed two-phase structure of (Fe,Cr)17RE2 and (Fe,Cr)3RE. Ce and Sm were concentrated in the Fe2RE and (Fe,Cr)17RE2 phases. The thickness of reaction zone in the Fe-Cr side grew in proportion to the square root of annealing time. The activation energy of the reaction zone growth was determined, which can be the basis of the cladding wastage modeling.