FCCI Barrier Coatings on U-10Zr Fuel

There is a need for improved fabrication methods for metal-cooled fast reactor fuels, especially metallic uranium- and plutonium-based fuels such as U-10Zr, using an approach that eliminates the ôsodium bondö used in more traditional approaches. The sodium bond is used as a thermal contact between the fuel slug and the cladding wall, until the slug expands sufficiently to make direct contact with the cladding wall. The Impact of eliminating the sodium bond are that recovery and recycling of the spent metallic fuel becomes much easier and the materials chemistry is easier as there is no need to protect against the high corrosivity of molten sodium in the fuel pin. approach is to insert the fuel slug into the cladding tube, then swage down the tube to make a tight fit of the cladding tube to the fuel slug, thus eliminating the need for the sodium bond. Some gaps or voids may still be present at this interface, but these can be bridged using helium gas (He bond). This approach would be used together with fuel pellets that have an annular cavity to take up fuel swelling expected during fuel burnup. To prevent Fuel Cladding Chemical Interaction (FCCI), We propose to explore different approaches for FCCI barrier or inhibiting layers that can be applied on the 1) outside of the fuel pellet, or 2) on the inside of the cladding tube. Objective 1. Demonstrate that we have achieved an intimate contact between the coated pellet and the stainless tubing after swaging and that any gaps that remain are < 25 microns. This will be confirmed with images of cross-sections made after swaging is completed. In addition, we will coat the inside walls of the HT9 cladding and swage down onto clean pellets. Objective 2. Demonstrate that FCCI ôgetterö coatings significantly decrease (less than 10X diffusion compared to samples made with no coating) the diffusion of the Nd, Ce or other lanthanides into the stainless steel after heating the cylindrical diffusion couples in a sealed container filled with Ar gas at temperatures ranging from 550°C to 700°C, for 100 hours. We will also test for diffusion of Fe and other HT9 constituents into the lanthanide pellet. This will be confirmed with SEM images and EDS chemical analysis of cross section samples at VT. Objective 3. Demonstrate that FCCI getter coating does not crack or create gaps and remains in-tack after the diffusion couple testing. This will be a single cycle of a thermal cycling test. In Phase I, we will work with both U-10Zr and pellets made of lanthanide alloys as a high burn- up surrogate for fuel pellets. technology will be used in next generation metal-cooled fast reactors. The public will benefit from cost reduced cost in a) manufacturing the fuel pins, b) increased life of the fuel assembly, and c) greater up-time and efficiency of the power reactor, thus lower electrical power cost rates.