Chromium-Based Mitigation Coatings on SiC Materials for Fuel Cladding
SiC composites are undergoing assessment under the Advanced Fuels Campaign for Light Water Reactors (LWR) as an Accident Tolerant Fuel (ATF) cladding. As noted, the main concern has been the hydrothermal corrosion of SiC under all LWR chemistries, resulting in cladding oxidation and recession unacceptable for the duration of burn-up. Improvements in future fuel burn-up further increase recession mitigation requirements. Hermeticity of ceramic cladding may also be a concern in terms of quality control. Coatings are being investigated as a practical solution to address concerns regarding SiC cladding for both accident conditions and normal operations. SiC materials were coated by various technologies to produce Cr-based mitigation coatings as a corrosion barrier in LWR water chemistry. In all cases, deposition of Cr compounds requires that SiC behave as a cathode during processing, which requires surface electrical conductivity. Morphology and phase analysis of the coatings are still undergoing investigation, mainly for predicting differential swelling, thermal expansion and microcracking. Autoclave corrosion and in-pile irradiation in a PWR water loop will follow in mid-2016. (authors)