Development of graded Ni-YSZ composite coating on Alloy 690 by Pulsed Laser Deposition technique to reduce hazardous metallic nuclear waste inventory

Highlights: → Pre-mature failure of vitrification furnaces not only delays nuclear waste immobilization process but also generates new type of wastes. → To prevent this, Ni-YSZ compositionally graded coating has been developed for Alloy 690 through Pulsed Laser Deposition technique. → Detail characterization of the coating and its behavior under simulated plant condition identifies Ni-YSZ composite coating as a suitable diffusion barrier material. - Abstract: Alloy 690 based 'nuclear waste vitrification furnace' components degrade prematurely due to molten glass-alloy interactions at high temperatures and thereby increase the volume of metallic nuclear waste. In order to reduce the waste inventory, compositionally graded Ni-YSZ (Y2O3 stabilized ZrO2) composite coating has been developed on Alloy 690 using Pulsed Laser Deposition technique. Five different thin-films starting with Ni80YSZ20 (Ni 80 wt% + YSZ 20 wt%), through Ni60YSZ40 (Ni 60 wt% + YSZ 40 wt%), Ni40YSZ60 (Ni 40 wt% + YSZ 60 wt%), Ni20YSZ80 (Ni 20 wt% + YSZ 80 wt%) and Ni0YSZ100 (Ni 0 wt% + YSZ 100 wt%), were deposited successively on Alloy 690 coupons. Detailed analyses of the thin-films identify them as homogeneous, uniform, pore free and crystalline in nature. A comparative study of coated and uncoated Alloy 690 coupons, exposed to sodium borosilicate melt at 1000 oC for 1-6 h suggests that the graded composite coating could substantially reduced the chemical interactions between Alloy 690 and borosilicate melt.