Cold spray coatings for accident-tolerant fuel cladding
Zirconium-alloy (Zr-alloy) fuel claddings have historically been used in Light Water Reactors (LWRs) for decades. These alloys perform extremely well in normal reactor operating conditions and survive complete in-reactor fuel cycles with minimal oxidation or degradation. However, if a reactor experiences a beyond-design-basis accident, such as loss of coolant to the core, Zr-alloys undergo a highly exothermic reaction with steam resulting in severe oxidation and associated hydrogen generation in the core. Therefore, this group has been developing several accident-tolerant fuel (ATF) coatings for Zr-alloy fuel cladding that are designed to withstand these severe accident scenarios.
Coatings are produced using cold spray, a solid-state deposition method that produces highly dense and adhered coatings with no oxidation of the powder during deposition. This group has produced several single-layer (MAX-phase Ti2AlC, pure Cr) and dual-layer (FeCrAl/Mo) ceramic and metallic coatings, with more advanced coatings under development. We are able to produce very thin (<30 µm) and continuous coatings that are oxidation resistant, cost-effective, and replicate the surface finish of conventional Zr-alloy cladding after post-processing.
Research and development includes characterizing feedstock powders and cold sprayed coatings using advanced characterization techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Coatings are subjected to a variety of testing in intense environments, such as high pressure water and steam autoclaves (1500-3000 psi), high temperature air and steam oxidation (1000-1500 °C), and neutron irradiation. This work is featured in several publications and three international patents have been filed. Additionally, recognition has been given from our collaborator, Westinghouse, for substantial contribution to their EnCore ® Fuel program, which has successfully produced full-length Cr-coated Zr-alloy lead test rods (LTR) scheduled for insertion in a commercial reactor in early 2019.
- Research and development of advanced dual-layer coatings
- TEM of feedstock powders and coatings to further understand coating formation
- In-depth observation of coating/substrate interface after high temperature testing
- Quantification of coating consumption after high temperature testing
- Finite element modeling of cold spray deposition process