Metallic Zirconium Internal Coating of Cladding Tube

Advanced technologies are desired for Advanced Reactors and fuels for sodium- and lead-cooled fast reactors. At reactor operating temperatures, inter-diffusion of the fuel, lanthanide fission products and the cladding can occur through the liquid metal bond and increasingly through direct contact resulting from fuel swelling. This inter-diffusion and the associated issues are referred to as “fuel-cladding chemical interaction” (FCCI), that may lead to (1) embrittlement and (2) relatively low-melting phases (eutectics), both of which compromise the physical integrity of the cladding and the fuel metal. As the fuel burnup increases, issues related to lanthanide fission products become more significant. The over-arching goal of this program is to develop a diffusion barrier of lanthanide fission products from the UZr fuel pellets into the cladding material. We developed and tested Zr, Mo, Cr and Nb ink and paste materials (and some combinations of Zr and Mo) and used them to coat coupons and tubes made from 316, 420 and HT9 stainless steel with thickness ranging from 10- 100 microns. The results varied depending on coating material and substrate material. Dense hermitic films of Zr were formed on HT9 with strong adhesion. No evidence of alloying Zr with the SS was observed. Mo formed dense coatings on all substrates but in some cases island formation was observed. Mo alloying with the SS was also suspected in some cases. In Phase II we will demonstrate a coating that will provide a diffusion barrier to FCCI. The goal will not be to block 100% of the lanthanide diffusion, but to demonstrate at significantly lower diffusion with the barrier as opposed diffusion with no barrier present at 600°C tested for 4-6 weeks in a diffusion couple experiment. Molten sodium and lead corrosion studies will also be conducted. This technology will be used in next generation nuclear reactors. The public will benefit from increased life of the fuel assembly and greater up-time and efficiency of the power reactor, lowering electrical power costs.