EVALUATION OF THE CORROSION KINETICS OF SIC WITH AND WITHOUT MITIGATION COATINGS IN LWR CHEMISTRIES

摘要

Since the Fukushima-Daiichi accident in 2011, accidenttolerantfuel (ATF) cladding concepts such as FeCrAlalloys and ceramic matrix composites (CMCs) of SiChave been extensively researched. SiC is desirable forexcellent radiation tolerance, mechanical properties, andresistance to oxidation under accident scenarios.However, under standard operating conditions, it maycorrode too quickly for use in LWRs. To mitigate theseissues, coatings of Cr, CrN, Cr/CrN, and TiN wereapplied via physical vapor deposition (PVD) on SiCprepared by chemical vapor deposition (CVD). Thesewere exposed, along with uncoated CVD SiC, totemperatures between 288 and 350°C, with 0.15-3 wppmdissolved H2 or 1-4 wppm O_2. TiN and CrN coatings didnot observe a permanently-protective oxide, potentiallydue to coating impurities. TiN was found to never beviable, slowly degrading in hydrogenated water, andspalling after ～0.5 μm of oxide growth. In HWC and PWRconditions, CrN did not perceptibly corrode but otherwisedegraded, while the multilayer Cr/CrN immediatelyfailed. Cr was a successful mitigation coating in theabsence of oxygen. The corrosion kinetics of the SiCsubstrate was dependent on the surface preparation, withpolished SiC leading to predictable linear kinetics, withone rate-limiting step for reactions with oxygen andwater.