The Novel Chlorination of Zirconium Metal and Its Application to a Recycling Protocol for Zircaloy Cladding from Spent Nuclear Fuel Rods
Date of Award
Doctor of Philosophy
Craig E. Barnes
David Jenkins, Bhavya Sharma, Jamie Coble
A novel protocol has been developed for the chemical removal of zirconium alloy (Zircaloy) cladding from spent nuclear fuel rods and subsequent isolation and purification of nuclear-grade zirconium chloride derived therefrom. This protocol is based on the chemistry developed from two new scientific findings.
First, two new oxidative chlorination reactions have been discovered for zirconium metal. In both solvents, zirconium can be quantitatively chlorinated at temperatures less than 150°C, with the operative equations seen below. In sulfur monochloride, the reaction is completed in 2 – 4 hours via surface etching, exhibiting 0th order kinetic behavior. The elemental sulfur byproduct can be quantitatively rechlorinated to sulfur monochloride immediately following the Zircaloy chlorination so the only consumable material from the reaction is chlorine. In thionyl chloride, the reaction is completed in 7 – 40 hours with a variable induction period. The time-to-completion may be lowered by increasing the temperature of the reacting metal or by utilizing a reagent to clean the surface. Based on previous studies, sulfur monochloride has been shown to clean the surface of the metal during reaction. Therefore, a mixture of sulfur monochloride and thionyl chloride may also be utilized to chlorinate zirconium, with a time-to-completion between 2 – 4 hours. The active chlorinating agent remains thionyl chloride.
Second, a new method to purify zirconium chloride from the chlorination reactions was investigated. It has been reported that zirconium chloride forms an adduct with thionyl chloride. However, to our knowledge, the solubility of the zirconium chloride in thionyl chloride has not been reported. The solubility is both high and temperature dependent in comparison to other metal chlorides investigated. This allowed for the development of crystallization procedures to obtain high yields of purified zirconium chloride. In the context of the recycling protocol for the Zircaloy, the product may either be decontaminated to reclassify it as low-level waste or reused by the industry.
This protocol has been performed in the presence of depleted uranium oxide pellets. Fuel pellets do not affect zirconium chlorination, and the chlorination does not alter the fuel pellets.
Vestal, Breanna K., "The Novel Chlorination of Zirconium Metal and Its Application to a Recycling Protocol for Zircaloy Cladding from Spent Nuclear Fuel Rods. " PhD diss., University of Tennessee, 2023.