Interaction study of molten uranium with multilayer SiC/Y2O3 and Mo/Y2O3 coated graphite

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Graphite crucibles are used for melting uranium and its alloys in VIM furnace. Various coating materials namely Al2O3, ZrO2, MgO etc. are applied on the inner surface of the crucibles using paint brush or thermal spray technique to mitigate U-C interaction. These leads to significant amount of carbon pick-up in uranium. In this study, the attempts are made to develop multilayer coatings comprising of SiC/Y2O3 and Mo/Y2O3 on graphite to study the feasibility of minimizing U-C interaction. The parameters are optimized to prepare SiC coating of about 70μm thickness using CVD technique on graphite coupons and subsequently Y2O3 coating of about 250μm thickness using plasma spray technique. Molybdenum and Y2O3 layers were deposited using plasma spray technique with 70μm and 250μm thickness, respectively. Interaction studies of the coated graphite with molten uranium at 1450°C for 20 min revealed that Y2O3 coating with SiC interlayer provides physical barrier for uranium-graphite interaction, however, this led to the physical separation of coating layer. Y2O3 coating with Mo interlayer provided superior barrier effect showing no degradation and the coatings remained intact after interaction tests. Therefore, the Mo/Y2O3 coating was found to be a promising solution for minimizing carbon pick-up during uranium/uranium alloy melting.