Investigation of Droplet Dispensing System for the Fabrication of Uniformly Sized Nuclear Fuel Microspheres Using Sol-Gel Method

The fabrication of nuclear fuel using powder metallurgical processes involves the handling of dry and fine powder that settles at various places and has the inherent cons of radiotoxic dust. Nuclear fuels comprised of plutonium or higher actinide oxide further pose long-term radiological and radiotoxic hazards. To minimize such hazards, alternate methods for the fabrication of fuels using the sol-gel method are being explored.A droplet dispensing system required for the fabrication of nuclear oxide fuel in the form of microspheres has been investigated and developed for the first time. This included the design and development of a sophisticated instrumentation setup, fabrication of the feed tank assembly, and an automatic droplet dispenser for the sol-gel process. This system will automatically dispense droplets of a radioactive broth solution into hot flowing silicone oil (90°C) to form uniformly sized microspheres.Due to the use of radioactive broth solutions and the complex process of microsphere preparation, the investigation and development of the instrumentation setup and methodology was complex. This will facilitate the fabrication of nuclear fuel with minimal human involvement in the remote operation. The broth solution, comprised of aqueous uranyl nitrate and complexing agents (hexamethylene tetramine and urea), was maintained at 5°C. This broth solution will be delivered at a constant flow (20 mL/min) through a nozzle and vibrator to the hot flowing silicone oil.At high temperature, these droplets chemically react to form microspheres. These soft microspheres are washed and heat treated to form hard microspheres. As the broth solution level falls in the feed tank, the back pressure above it also decreases. This serves as a feedback to the connected pressure regulator, which then pressurizes the feed tank. A constant flow of fuel broth solution is thus maintained by the mass flow controller. The droplet system has been calibrated, tested and validated with water and a nitrate solution. Now, the system has been deployed at the site for the fabrication of microsphere of uranium oxide fuel.