Recycling Off-Grade Zircaloy Scrap Using a Molten-Salt Electro-Refining Process

Zircaloy hardwares meant for use in nuclear power reactors have to meet very stringent nuclear, metallurgical, and mechanical specifications. For this purpose, many complex chemical, metallurgical, and manufacturing processes have to be gone through. In view of these factors, the conversion yield from sponge to Zircaloy hardwares varies from 25 to 40%. The low recovery, low hafnium content in scrap, and the cost factor necessitate recycling of scrap to maximum extent. A variety of processes have been developed for treating and recycling of scrap. A major portion of the remeltable stock is treated in an inert-gas plasma melting furance to make a consumable electrode which is further vacuum arc melted. The odd shape scrap is broken down by hydriding-dehydriding for mixing with sponge for further processing by vacuum arc melting. The non-remeltable stock, where the degree of contamination with respect to interstitials is high, needs chemical processing. Two methods, chlorination and Kroll reduction and molten-salt electro-refining, have been attempted. In the first process, the scrap is converted into ZrCl4 which is subsequently reduced to sponge by the Kroll process. In the molten-salt electro-refining process, the scrap is converted into zirconium dendrites in NaCl-K2ZrF6 or NaCl-NaF-ZrCl4 bath. The product obtained by the electro-refining process meets reactor-grade specifications. This paper describes briefly the foregoing methods of recycling Zircaloy scrap at the Nuclear Fuel Complex, Hyderabad, India, with a critical review of the molten-salt electro-refining method.