Can Plasma Decontamination Etching of Uranium and Plutonium be extended to Spent Nuclear Fuel Processing?

Glow discharge and atmospheric pressure plasma processes have been studied in applications for decontamination of plutonium (Pu) and uranium (U) contaminated objects. In these processes, U or Pu contamination on objects such as gloveboxes are converted to a volatile metal hexafluoride which can be pumped away leaving the object free of contaminants. It appears feasible to apply this technology to recovering spent fuel without the large waste by-products of present wet chemistry processes. The plasma etch rates are rapid in bulk but are eventually quenched in the decontamination process as non-volatile chemical products build up on or near the contaminated surface. A pulsed plasma system has been proposed that reduces or eliminates the quenching action while continually exposing new bulk U material in the spent fuel. There are several advantages of plasma reprocessing over existing aqueous acid- or flame-based methods: 1) plasma is a dry process in which no liquid wastes are generated, 2) plasma is a fast process in which reactive species produced in the plasma increase reaction rates significantly over chemical processes, 3) plasma is a low temperature process whereby the electron temperature is high but the ion temperature is low thereby eliminating serious material issues observed in flame-based techniques while preserving the high electron energies needed to break chemical bonds, 4) the plasma method does not rely on stoichiometric mixtures of U and the reactive ion since the acceleration energy in the plasma sheath can easily break chemical bonds, and 5) plasma is a safe and reliable process because toxic chemicals in wet chemistry (e.g., F2) can be replaced with nontoxic and relatively inexpensive CF4 or NF3 source gases. The application of a plasma process to recycling spent fuel would significantly reduce the amount of waste generated while reducing the cost of reprocessing.