Hydrothermal Corrosion of Coatings on Silicon Carbide in Boiling Water Reactor Conditions

SiC/SiC ceramic matrix composites are an attractive material for use as accident tolerant fuel cladding. However, despite its resistance to corrosion in high-temperature steam, SiC is known to dissolve in high-temperature water, necessitating the use of corrosion-resistant coatings. Here, samples were exposed in 288°C water with 2 ppmw dissolved oxygen to simulate boiling water reactor (BWR) normal water chemistry (NWC) and 288°C water with 150 ppbw dissolved hydrogen to simulate BWR hydrogen water chemistry. Several candidate coatings were tested: Cr, CrN, TiN, and ZrN. All coatings were applied by physical vapor deposition onto chemical vapor deposition SiC (CVD-SiC) substrates. Two uncoated SiC/SiC variants were also exposed and degraded more rapidly compared to CVD-SiC, especially in NWC. Cr and CrN coated specimens were found to have low mass change, suggesting they are promising candidate coatings. Lastly, TiN coatings were found to oxidize rapidly, suggesting that coatings would fully oxidize during service in BWR environments. ZrN coatings dissolved completely during exposure.