Neptunium - Uranium - Plutonium Co-Extraction in TBP-based Solvent Extraction Processes for Spent Nuclear Fuel Recycling

The US, through the Global Nuclear Energy Partnership, is currently engaged in efforts aimed at closing the nuclear fuel cycle. Neptunium behavior is important to understand for transuranic recycling because of its complex oxidation chemistry. The Pacific Northwest National Laboratory is investigating neptunium oxidation chemistry in the context of the PUREX process. Neptunium extraction in the PUREX process relies on maintaining either IV or V oxidation states. Qualitative conversion of neptunium(V) to neptunium(VI) was achieved within 5 hours in 6 M nitric acid at 95 deg. C. However, the VI state was not maintained during a batch contact test simulating the PUREX process and neptunium reduced to the V state, rendering it inextractable. Vanadium(V) was found to be effective in maintaining neptunium(VI) by adding it to a simulated irradiated nuclear fuel feed in 6 M nitric acid and to the scrub acid in the batch contact simulation of the PUREX process. Computer simulations of the PUREX process with a typical irradiated nuclear fuel in 6 M nitric acid as feed indicated little impact of the higher acid concentration on the behavior of fission products of moderate extractability. We plan to perform countercurrent tests of this modified PUREX process in themore » near future. (authors)« less