Materials Performance in a Radioactive Waste/Glass Melter System Environment

Corrosion coupons were exposed in a scale demonstration melter system in order to evaluate the performance of alternate materials for use as top head and off gas components in the Defense Waste Processing Facility (DWPF) melter at the DOE`s Savannah River Site. The demonstration system is a 1/10 scale prototypic version of the DWPF melter. In DWPF, high activity radioactive waste will be vitrified and encapsulated for long-term storage. Fifteen different nickel and cobalt base alloys were exposed for five months to corrosive vapors and molten glass, characteristic of the DWPF melter except for radioactivity. Process conditions included temperatures approaching 900{degree}C and a synthetic acid waste containing formates, halides, sulfates, phosphates, nitrates, and mercury. Severe oxidation of the N06625 in both the splash zone and vapor space was attributed to the formation of MoO{sub 3}. Cobalt containing alloys experienced significant degradation in this environment. Results of the metallurgical examination showed that alloys containing 50 wt % Ni, 25 wt % Cr, and additions of 2 to 3 wt % of either aluminum or silicon performed comparably or better than the N06690 in both the splash zone and in the vapor space near the lid. Corrosion rates for these alloys didmore » not exceed 0.2 mm per year (8 mpy).« less