Possible Methods of Reprocessing
Aqueous Processes
UREX Process
The Urex Process is a PUREX process modified by adding the reductant before the first extraction step, so that the plutonium will not be separated with the uranium. The key is the addition of acetohydroxamic acid (AHA) to the extraction and scrub sections of the process. The addition of AHA greatly diminishes the extractability of plutonium and neptunium. This makes the reprocessing process more proliferation resistant.
TRUEX
The TRUEX (TRansUranic Extraction) process was developed by the Argonne National Laboratory. It is designed to lower the alpha activity of the transuranic metal waste.
DIAMEX
The DIAMEX (Diamide Extraction) process is being developed by the French Commissariat à l’Énergie Atomique. The DIAMEX process has the advantage of avoiding the production of organic waste with elements other than carbon, hydrogen, nitrogen and oxygen. The organic waste can then be burned without the formation of acidic compounds that would contribute to acid rain. The process has been well-researched and an industrial plant could be constructed to use this process.
UNEX
The UNEX (Universal Extraction) process was developed Russia and the Czech Republic and it was designed to remove all the undesirable radioisotopes left after the uranium plutonium extraction.
Non-aqueous Processes
Pyroprocessing
Pyroprocessing is a generic term for pyrometallurgy processes. They were developed at the Argonne National Laboratories, yet they are not in current use due to the fact that reprocessing plants are not being built. The reprocessing plants that have already been built employ the PUREX processes. If Generation IV reactors become more popular in the future, pyroprocessing could become more popular.
What is pyroprocessing?
Pyroprocessing employs the electrorefining technique. The spent nuclear fuel rod in a steel basket serves as an anode and a solid iron and liquid Cd serve as the cathodes in a molten chloride bath at 500 degrees C. As a voltage is applied between the electrodes, the fuel rod dissolves into the molten salt and the actinides form chlorides in the molten solution. The uranium is selectively recovered at the solid cathode due to the less negative free energy change it has compared to the transuranic elements. The transuranium elements such as plutonium, neptunium, americium, and curium are collected at the liquid cadmium cathode along with uranium. The fuel that is recovered can be used in a Molten Salt Transmutation Reactor.
Figure: The Electrorefining Technique
Advantages of Pyroprocessing
One advantage of the pyroprocessing technique is that it does not use water. Water is easily contaminated and not easily cleaned up. The fuel also contains a large percentage of actinides, which makes the fuel useable in reactors but difficult to make nuclear weapons from. The PUREX process separates out the actinides from the uranium and plutonium, which creates more dangerous nuclear waste. Pyroprocessing is more compact than aqueous processes, which allows on-site reprocessing of spent nuclear fuel rods. This will eliminate the need for the transportation and security of the hazardous waste.
