Advanced Metallic-Silicon Carbide Composite Claddings for Improved Damage Tolerance

The recent events at the Fukushima nuclear power plant highlight the need for enhanced accident tolerance. Of particular concern is the overheating of standard zirconium alloy cladding in a loss of coolant accident (LOCA). One of the leading, high-risk/high-reward candidates for future claddings is a silicon carbide (SiC) composite. However, the inherent open porosity present in fibrous based composites leads to an intrinsic lack of hermeticity for a fully-composite cladding. Some SiC clad designs seek to overcome this issue through one or more ceramic coatings, though such coatings are also intrinsically brittle; thus, raising the question as to the ability to withhold fission products. While fission product retention is still an open question in the community, recently published work suggests that a fully-ceramic design has serious issues. Recent results have shown a hybrid design comprised of a SiC composite cladding with a thin metallic coating can provide the desired hermetic properties. In addition, initial bond strength and irradiation tests of metallic coated SiC composite claddings have produced extremely promising results. However, the mismatch in coefficients of thermal expansion between the metallic coating and the SiC composite can result in high thermal induced stresses during fabrication or service, which can cause cracks or bonding issues. During this investigation, innovative additive manufacturing techniques will be developed that will enable the tailoring of the transition region between the hermetic metallic topcoat and the underlying SiC composite cladding to minimize thermal induced stresses. As a result, the use of more corrosion resistant metallic coatings will be possible; thus, a more damage tolerant cladding will be produced. During Phase I, the techniques for producing dense, well-bonded, oxidation resistant coatings on SiC will be developed. Samples will be produced for preliminary testing and analysis at Massachusetts Institute of Technology as part of the Accident Tolerant Fuel (ATF) Integrated Research Program. During Phase II, the fabrication techniques will be optimized. Prototypical fuel rods with the improved cladding will be fabricated and tested at relevant reactor conditions. Fuel rods for safe commercial nuclear power in USA and throughout the world. Other applications include naval nuclear power, and protecting composites in aircraft from oxidation.