Key technical gaps must be addressed to enable commercialization, including the development of effective sealing technologies.

The Fukushima accident has renewed interest in potentially safer nuclear fuel designs. One option being considered is the use of silicon carbide (SiC) as a cladding material. The high-temperature properties of SiC offer many advantages over conventional metal-based fuel materials, especially under loss of coolant accident (LOCA) conditions. The structural and chemical stability of SiC at elevated temperatures offers several benefits, such as the elimination of hydrogen production and maintenance of fuel integrity for longer durations in a LOCA event.

EPRI became involved in SiC research in 2008, initially in a support role to develop a fuel rod end plug seal and to conduct an economic viability evaluation. The sealing of SiC fuel rods represents one of the main obstacles to the development of the technology. Several diffusion and reaction based sealing approaches have been tried with limited success. EPRI is evaluating other variations of diffusion bonds and results are expected some time in 2012. EPRI also has conducted an economic assessment of SiC as a fuel cladding material. The analysis indicates that SiC clad fuel is viable provided that the fabrication cost of SiC-based clad is not significantly different than that of conventional cladding.

One possible nearer-term application for SiC is as a channel material in boiling water reactors (BWRs). Nuclear fuel in BWRs is typically placed inside a long square channel typically made from a zirconium-based alloy. The channel functions to hydraulically isolate the fuel and to provide support to control rods. The use of SiC in this application could eliminate a phenomenon called "channel bow" that is currently experienced by metal-based BWR channel boxes. If not detected and addressed, channel bow can potentially lead to control rod insertion issues and reduced shutdown margin. This application may be more promising than SiC cladding because a hermetic seal is not required for proper functioning of the component. EPRI is fabricating several test articles to evaluate fragmentation resistance and properties under irradiation conditions. The irradiation testing is to be conducted in cooperation with the Idaho National Laboratory.

For more information, contact Ken Yueh at 704.595.2613 or kyueh@epri.com.