Non-destructive Screening During Fabrication for High Strength SiC Ceramic 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. While the safety benefits of advanced ceramics are attractive in their own right, there are other desirable characteristics that further increase the attractiveness of these materials, including the maintenance of strength and neutron and thus power generation) efficiency which have their own benevolent cascades. A concern in evaluating the use of these materials is the reliability of ceramic material under the mechanical loading conditions in a nuclear reactor. Due to the nature of ceramic production, there is a concern that design loads must be kept extremely low to ensure reliability on par with current technology. A second deterrent is the current cost of production of these materials. In the research quantities these materials are currently produced, cost is an order of magnitude higher than the rival metallics on a per-foot basis. As the industry moves towards manufacturing for commercial use, economy of scale alone cannot be expected to narrow this cost differential. Each incremental step that addresses a large-scale manufacturing challenge increases the chances that advanced ceramic claddings can be introduced to the market as a viable replacement for conventional metallic clads for nuclear fuels in light water reactors. The non-destructive inspection techniques proposed in this project are expected to identify material that will not meet certain mechanical strength requirements, allowing the manufacturer to prevent this material from being deployed. This will increase the reliability of the delivered material. Using the inspection techniques from this project at the identified juncture of the manufacturing process is expected to make a significant cost savings for the manufacturer, enabling this material to become more cost competitive with conventional metallic materials. Decreasing the cost of production and establishing a uniform process that produces material of consistent quality will make advanced ceramics a more cost-competitive technology for fuel cladding. In Phase I, a number of silicon carbide tubes will be ultrasonically examined as a screening method for non-conforming material. The efficacy of this screening will be determined by destructive strength tests, with the ultimate goal to demonstrate that the methods proposed will reliably identify material that does not meet strength requirements. New design envelopes will be developed based on the results. If successful in Phase I, a Phase II program will be proposed to assemble a more powerful and higher resolution inspection devise and demonstrate the ability to screen for even more stringent strength requirements. The technology of this product is not limited to any of the specific designs currently proposed, and is thus applicable for use with any of the expected ceramic fuel clad manufacturers. The technique is appropriate to any ceramic manufacturer. The current market for cladding is over 150,000 linear feet annually for each light water nuclear reactor, with a fleet of over 450 reactors worldwide. This technology reduces the cost of production, and as such, alone, could be worth a minimum of a $200,000 less in cost of production of fuel assemblies, annually, for each reactor that adopts ceramics for their safety benefits. Over the entire US fleet, this is a considerable savings of over $30 million annually.