Functionally Graded NiMo Overlays for Improved Corrosion Resistance in Molten Salts

Abstract

The use of molten halide salts as a primary coolant within next generation molten salt nuclear reactors (MSRs) has the potential to improve efficiency and nuclear reactor safety by operating at low pressures and high temperatures without boiling. However, these coolants will require the development of new corrosion resistant material systems that will have to meet or supersede existing standard codes for these systems. Therefore, new MSRs will require validation and testing of new material systems that can produce robust component structures and enable them to withstand these corrosive environments.

In this paper we will discuss a new low cost and diffusion bonded functionally graded NiMo alloy overlay for next generation molten salt reactors. The application of this material involves applying a functionally graded NiMo overlay by electrodeposition onto wrought 316H stainless steel (SS) substrates. After application, the overlay was diffusion bonded to the substrate by hot isostatic pressing (HIPping). This application process has been demonstrated under static corrosion conditions with 316H SS flat coupons (0.7 x 1.3 x 0.3 cm) and pipes (1” ID 8” long). The initial static corrosion studies in FLiNaK at up to 750°C for 1000 h are promising with no corrosive attack of the underlying 316H SS substrate.