Review Article: The Effects of Radiation Chemistry on Solvent Extraction: 1. Conditions in Acidic Solution and a Review of TBP Radiolysis

The partitioning of the long-lived -emitters and high-yield fission products from dissolved nuclear fuel are key components of processes envisioned for the recycling of nuclear fuel and the disposition of high-level waste. These future processes will likely be based on aqueous solvent-extraction technologies for light-water reactor fuel and consist of four main components for the separation of uranium, fission products, group trivalent actinides, and lanthanides, and finally the separation of the trivalent actinides from the lanthanides. Since the solvent systems will be in contact with highly radioactive solutions, they must be robust toward radiolytic degradation in an irradiated mixed organic, acidic aqueous environment. Therefore, an understanding of their radiation chemistry is important to the design of a practical system. In this paper we review the radiolytic production of the reactive species expected to be present in such an irradiated system and predict which radiolytically-produced species are available for reaction with solvent extraction ligands. We then review the literature on the radiation chemistry of tributyl phosphate, the ligand used in uranium extraction in the first step in the series of four extractions proposed for the new fuel cycle.