Binary Metal Ceramic Tubes for Accident Tolerant LWR Fuel Cladding

The use of advanced ceramic materials, such as silicon carbide, for light water reactor fuel cladding is being investigated, in part due to the increased safety margin afforded by this technology over conventional zircaloy metallic claddings. In light of the Fukushima events, safety concerns have come to the forefront of public scrutiny of commercial nuclear generated power and spurred activity in this arena. A deterrent to the silicon carbide cladding are concerns that the material may not provide a hermitic barrier for the fission gases produced by the fuel. A binary clad that uses a zircaloy inner tube, which can ensure a hermitic seal, with an outer layer of silicon carbide addresses this concern. Previous attempts at developing this type of cladding have involved building the composite material on the ziracloy tube, but these attempts have failed because the temperatures required to achieve a composite structure damage the zircaloy tube. An economical process needs to be developed for fabricating this binary cladding, which combines the best features of the traditional metal (zircaloy) cladding, with the extraordinary accident tolerance of ceramic (silicon carbide) cladding. How the Problem is Being Addressed: The process for fabricating a silicon carbide tube with the necessary strength and corrosion properties has been developed over the last 10 years. In order to ensure that the composite tube meet the necessary requirements, the composite tube could be fabricated separately from the zircaloy tube rather than building the composite around it. Then in a secondary operation, the zircaloy tube could be expanded to contact the silicon carbide outer tube. Phase I Approach: In Phase I, thin-walled zircaloy tubing will be received from an existing supplier and silicon-carbide outer tubes will be manufactured. Then a process will be developed for expanding the inner zircaloy tube to be in intimate contact with the outer silicon carbide tube. A sample of the binary clad will be produced using the process. A finite-element model of the binary clad will be developed and analyzed. Commercial Applications: If the Phase I research is successful, a Phase II project will be proposed to fabricate closed binary clad cylinders that are sized to the required 17 x 17 clad geometry, and arrange for mechanical and steam exposure testing of the final product to demonstrate accident tolerance. Fueled test specimens will be prepared for test reactor irradiation testing. If successful, the technique will offer a viable option for accident tolerant fuel cladding. Key Words: Nuclear Fuel, Ceramic Cladding, Silicon Carbide, Corrosion Resistant,