PUREX

PUREX
source
Name	PUREX
Type	Nuclear reprocessing
Industry	Nuclear fuel cycle
Inventor	Herbert H. Anderson, Larned B. Asprey
Developed	Manhattan Project, Argonne National Laboratory
Related	REDOX, THOREX, DIAMEX, SANEX

PUREX. The PUREX process is the dominant industrial method for the reprocessing of used nuclear reactor fuel. It is a liquid-liquid extraction procedure designed to separate Plutonium and Uranium from each other and from other fission products. The process has been central to both civilian nuclear power programs and military weapons production since the mid-20th century.

Overview

The primary objective is the recovery of valuable fissile materials from spent fuel assemblies. This separation is achieved using the organic solvent Tributyl phosphate dissolved in a hydrocarbon diluent such as odorless kerosene. The process operates on an industrial scale at facilities like the La Hague site in France and the Sellafield site in the United Kingdom. Its implementation has significant implications for the management of high-level waste and the potential recycling of nuclear materials.

Process description

Irradiated fuel rods are first dissolved in hot concentrated Nitric acid. This aqueous solution, containing uranium, plutonium, and numerous fission products, is then contacted with the TBP/kerosene mixture in equipment such as pulse columns or Mixer-settlers. Uranium and plutonium are selectively extracted into the organic phase, while most fission products remain in the aqueous Raffinate. Subsequent stripping steps use reducing agents to separate plutonium from uranium. The final products are purified Uranyl nitrate and Plutonium nitrate solutions.

History and development

Early research was conducted during the Manhattan Project at the Metallurgical Laboratory in Chicago. Key chemists including Glenn T. Seaborg and Stanley G. Thompson pioneered Actinide chemistry. The modern process was developed in the late 1940s and 1950s, with crucial contributions from scientists at the Argonne National Laboratory and the Savannah River Site. The first large-scale plant began operation at the Savannah River Site in 1954. The process was later adopted and refined by nations such as France, the United Kingdom, Russia, and Japan.

Applications and use

The primary application has been the production of weapons-grade plutonium for national nuclear arsenals, notably by the United States Department of Energy and the former Soviet Union. In civilian contexts, it enables the recovery of uranium and plutonium for reuse as Mixed oxide fuel in reactors like PWRs and BWRs. Major reprocessing plants operating the process include AREVA's La Hague facility and BNFL's THORP plant at Sellafield. It also plays a role in the closed fuel cycle.

Chemical reactions and mechanism

The core extraction relies on the formation of neutral complexes between metal ions and TBP. Uranium is extracted as UO₂(NO₃)₂·2TBP. Plutonium is extracted in the +4 oxidation state as Pu(NO₃)₄·2TBP. The distribution coefficients are highly dependent on the concentration of Nitric acid. The separation of plutonium from uranium is achieved by reducing plutonium to the +3 oxidation state with agents like Ferrous sulfamate or Hydroxylammonium nitrate, which does not form an extractable complex with TBP.

Alternatives and related processes

The REDOX process, using Methyl isobutyl ketone, was an early competitor. For fuels with high Plutonium-240 content, the UREX process was developed. The THOREX process is designed for reprocessing thorium-based fuels. Modern research focuses on Partitioning and transmutation strategies using processes like DIAMEX (for Actinide separation) and SANEX (for Lanthanide/actinide separation). Other advanced methods include Pyroprocessing and investigations using Ionic liquids or Supercritical fluids.

Category:Nuclear reprocessing Category:Industrial processes Category:Radiochemistry