Development of titanium diffusion barrier coatings for mitigation of fuel–cladding chemical interactions

Abstract

High temperature and radiation in nuclear reactors result in inter-diffusion and reaction between fuel and cladding. This phenomenon is called fuel–cladding chemical interactions (FCCI). It reduces the effective cladding wall thickness and might lead to eutectic liquation. Having a thin diffusion barrier coating inside the cladding can potentially reduce or postpone the onset of FCCI. This study examines the feasibility of using a nanofluid-based electrophoretic deposition (EPD) process to deposit titanium metallic coating as the diffusion barrier. The deposition parameters, including the nanofluid solvent, additive, particle size, current, and voltage were optimized using test flat substrates of T91 ferritic–martensitic steel. Postdeposition sintering was also conducted and optimized to achieve the best bonding and mechanical integrity. These diffusion couple studies were performed at 575°C for 100h between cladding and cerium as the fuel surrogate. Results showed that titanium coatings significantly reduced the solid state inter-diffusion between cerium and steel. Using a co-axial EPD, titanium was successfully deposited uniformly on the inner surfaces of 12″ length of cladding with 4mm inner diameter. Such a coating is extremely difficult to manufacture by conventional coating technologies like thermal spray or vapor deposition.