DIAMEX

DIAMEX. The DIAMEX (DIAMide EXtraction) process is a liquid-liquid extraction method developed for the selective separation of minor actinides from spent nuclear fuel. It utilizes malonamide extractants to co-extract trivalent americium and curium from highly active raffinates produced by the PUREX process. This technology is a cornerstone of advanced nuclear fuel cycle research aimed at reducing the long-term radiotoxicity and heat load of high-level waste destined for geological repositories.

Overview

The process was pioneered by chemists at the Commissariat à l’Énergie Atomique in collaboration with the European Commission's research programs. It operates within the broader framework of partitioning and transmutation strategies, which seek to convert long-lived actinides into shorter-lived fission products. Key pilot-scale demonstrations have been conducted at facilities like the MARCoule Nuclear Site in France and the JRC Karlsruhe in Germany. The development of DIAMEX has been significantly advanced through multinational projects such as PARTNEW and EUROPART, fostering cooperation between entities like ITU Karlsruhe and the Chalmers University of Technology.

Chemical Process

The core of the methodology involves the use of diamide ligands, such as DMDOHEMA, dissolved in an aliphatic diluent like TPH. These extractants form complexes with trivalent metal ions from an aqueous nitric acid solution. The chemistry is designed for high selectivity, effectively separating lanthanides and actinides from other fission products like cesium, strontium, and platinum group metals. Subsequent process steps, often involving the SANEX group of techniques, are required to achieve the crucial separation of americium and curium from the chemically similar lanthanides, a challenge addressed by processes like SESAME and EXAm.

Development and History

Research into diamide extractants began in the late 1980s, with the first DIAMEX process flowsheet proposed in the early 1990s. Major milestones were achieved during the NEWPART and PARTNEW projects under the Fourth Framework Programme of the European Atomic Energy Community. Successful continuous hot tests were performed at the MARCoule Nuclear Site using genuine high-level waste solutions. Further optimization occurred through the ACSEPT and SACSESS projects, which investigated solvent stability and improved separation factors. Parallel development work has also been conducted in Japan by the Japan Atomic Energy Agency and in Russia at the Khlopin Radium Institute.

Applications and Significance

The primary application is within advanced nuclear fuel cycles, such as those proposed for Generation IV reactor systems, to support the transmutation of minor actinides in facilities like fast neutron reactors or accelerator-driven systems. By removing these elements, the process significantly reduces the long-term hazard of vitrified waste, potentially easing the safety case for deep geological disposal sites like the planned Deep Geological Repository in Finland or Sweden's SFR Forsmark. It represents a key technological pillar for countries pursuing a closed fuel cycle policy, impacting waste management strategies at major facilities like the La Hague site and the Sellafield site.

Comparison with Other Processes

Unlike the PUREX process, which targets uranium and plutonium, DIAMEX is specialized for trivalent actinides. Compared to the American-developed TRUEX process, which uses a CMPO extractant, DIAMEX offers the advantage of being "CHON" (composed only of carbon, hydrogen, oxygen, and nitrogen), facilitating complete incineration of spent solvent. The SANEX processes are often complementary, designed for the subsequent separation of actinides from lanthanides. Other competing approaches include the TALSPEAK process and the use of bis-triazinyl pyridine ligands, each with different profiles in terms of selectivity, acidity requirements, and robustness under intense radiation fields. Category:Nuclear reprocessing Category:Radiochemistry Category:Separation processes