The Effects of Radiation Chemistry on Solvent Extraction 4. Separation of the Trivalent Actinides and Considerations for Radiation-Resistant Solvent Systems
The separation of the minor actinides from dissolved nuclear fuel is one of the more formidable challenges associated with the design of the advanced fuel cycle. The partitioning of americium and its transmutation in fast reactor fuel would reduce high-level-waste long-term storage requirements by as much as two orders of magnitude. However, the lanthanides have very similar chemistry. They also have large neutron capture cross sections and poor metal alloy properties and thus they can not be incorporated into fast reactor fuel. A separation amenable to currently existing aqueous solvent extraction processes is therefore desired, and research is underway in Europe, Asia and the USA toward this end. Current concepts for this final separation rely on the use of soft-donor nitrogen or sulfur-containing ligands that favor complexation with the 5f orbitals of the actinides. In the USA, the most developed process is the TALSPEAK (Trivalent Actinide Lanthanide Separation by Phosphorous reagent Extraction from Aqueous Komplexes) process, based upon the competition between bis(2-ethylhexyl)phosphoric acid (HDEHP) in the organic phase and lactate-buffered diethylenetriamine pentaacetic acid (DTPA) in the aqueous phase. In Europe and Japan, current investigation is focused on the BTP diamide mixtures or dithiophosphinic acids. Any process eventually adopted must be robust under conditions of high-radiation dose-rates and acid hydrolysis. The effects of irradiation on solvent extraction formulations may result in: 1) decreased ligand concentrations resulting in lower metal distribution ratios, 2) decreased selectivity due to the generation of ligand radiolysis products that are complexing agents, 3) decreased selectivity due to the generation of diluent radiolysis products that are complexing agents, and 4) altered solvent performance due to films, precipitates, and increased viscocity. Many of the ligands associated with minor actinide/lanthanide separations are relatively new. Unlike their predecessors, many have been designed with radiation chemical principals in mind. The evolution of the BTPs and diamides show attention to these details, and a series of structural modifications have evolved that are meant to address them. In this fourth and final part in the series we report on the radiation chemistry of the minor actinide separations processes. We also provide a summary of the general radiolysis reactions that have implications for all ligand and diluent systems.
- Research Organization:
- Idaho National Lab. (INL), Idaho Falls, ID (United States)
- Sponsoring Organization:
- DOE - NE
- DOE Contract Number:
- DE-AC07-05ID14517
- OSTI ID:
- 983945
- Report Number(s):
- INL/JOU-09-17122; ISSN 1532-2262; TRN: US1005206
- Journal Information:
- Solvent Extraction and Ion Exchange, Vol. 28, Issue 4; ISSN 0736-6299
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ACID HYDROLYSIS
ACTINIDES
CHELATING AGENTS
CHEMISTRY
CROSS SECTIONS
DOSE RATES
FAST REACTORS
FUEL CYCLE
NEUTRON REACTIONS
NUCLEAR FUELS
RADIATION CHEMISTRY
RADIATIONS
RADIOLYSIS
RARE EARTHS
SOLVENT EXTRACTION
SOLVENTS
actinide extraction
BTPs
dithiophosphinic acids
free radicals
G-values
lanthanide extraction
radiation chemistry
TALSPEAK