[en] A number of analytical techniques can be applied to quantitative measurements of oxidation state distribution among the actinide elements. The techniques discussed in regard to their limitations and advantages are: electrophoretic ion focusing, visible absorption spectroscopy, nuclear magnetic resonance spectroscopy, laser (thermal lensing, photoacoustic and time resolved) spectroscopies and x-ray absorption (EXAFS and XANES) spectroscopies. Chemical separations utilising precipitation, sorption, solvent extraction, and ion exchange have been used to separate actinides in various oxidation states at tracer levels. Examples of methods involving chemical separations, which have been demonstrated to be useful in obtaining data on redox distributions, are reviewed with emphasis on their limitations and the conditions for successful application. (author)

[en] The extraction behaviour of technetium, thorium, uranium, neptunium, plutonium, americium and curium in the Aliquat-336 (diluted with 1.3-diisopropyl benzene) nitric acid system has been studied. Aliquat-336 (tri-capryl methyl ammonium nitrate) is a quaternary ammonium salt extracting different species with an anion exchange mechanism. Distribution data obtained are modelled by anion exchange (Tc) and ion-pair formation mechanisms (actinides) with the extraction of nitric acid included to account for the lowering of the free extractant concentration. (author)

[en] A technology and a protocol were developed for laboratory-scale determination of the distribution coefficients of uranium, representing the actinides and lanthanides. The separation was performed at 720 deg C by selective reduction of actinides fluorides by magnesium. The experimental results show that the distribution of species between the two phases diverges from the ideal situations; this is attributed to infinite-dilution activity coefficients far from 1 for the solutes. Under these conditions, uranium can be separated from lanthanum by carefully controlling the concentration of reducing agent. Regarding kinetics, it seems that the limiting factor is the chemical reaction. (author)

[en] The Act of the French Parliament passed on 30 December 1991 concerning the management of high activity, long-lived nuclear wastes identifies three main lines of research: the separation of long-lived elements for their transmutation, repository in deep geological formations and, third, conditioning and interim storage. In each of these fields, the research organisation involved are required to provide the necessary scientific and technical assessments before the year 2006 to enable the public authorities to make the appropriate strategic decisions. The French Atomic Energy Commission (CEA) drew up the SPIN programme as a response to the first axis of the Act: it essentially involves investigation on the separation and transmutation of the long-lived radionuclides present in spent nuclear fuel. (author)

[en] The CEA has undertaken the development of the DIAMEX process, which uses diamide extractants to separate minor actinides from fission products in HLLW. Preliminary counter-current hot tests had confirmed the feasibility of the concept and identified various directions for further development. The first two parts deal with the experimental works conducted to identify the degradation products and to optimise the extractant formula. The available results enable us to propose a new formula for the diamide molecule designed to enhance the solubility of the complexes, affinity for actinides (III) and extractant regeneration. The last part concerns the work done to improve the DIAMEX basic flowsheet, especially to prevent Zr and Mo extraction. (author)

[en] Resorcin-arene based CMP(O)-ligands (1-4) are powerful extractants for Eu(III) (used as general representative for the lanthanides and trivalent actinides). At higher acidity (pH<1) protonation of the ligand occurs resulting in decreasing distribution ratio. Within the lanthanide series the distribution ratio varies with decreasing ionic radii. Application of ligand 1 in Supported Liquid Membrane extractions allows the quantitative removal of Eu(III) from medium acidic nitrate solutions. (author)

[en] In the partitioning-transmutation (p-t) nuclear fuel cycle, the separation of actinides(III) from lanthanides(III) is essential because of the high neutron absorption cross-sections of some rare earth nuclides. Group separation represents one of the most difficult challenges in the field of separation science. The solvent extraction of trivalent actinides and lanthanides from aqueous 1 M NaNO₃ by means of the sulfur-containing acidic extractant Cyanex 301 was studied. Efficient separations were observed with unpurified Cyanex 301 for high Ln(III) concentrations, but not for low Ln(III) concentrations. Very high An(III)/Ln(III) separation factors (higher than 10³) were obtained with purified Cyanex 301 for micro or macro concentrations of Ln(III) at pH 3-4. By means of a synergistic mixture of aromatic di-thio-phosphinic acid and tributylphosphate a successful Am(III(/lanthanides separation from 0.2 M HNO₃ was demonstrated. This is in contrast to Cyanex 301, which extracts trivalent actinides selectively, without synergist, but at a relatively high pH 3-4. (author)

[en] The main goal of the SPIN program developed by CEA is to improve the management of high activity waste containing minor actinides and long-lived fission products. In that field, americium has been pointed out as the main hazardous element to be firstly recovered. With the aim to extract more than 99% of the americium contained in high-level liquid waste, the SESAME process, which consists in the selective extraction of oxidised Am is foreseen as a promising way to succeed in Am management. Dealing with the americium selective recovery from HLLW, many studies concerning the electrochemical oxidation of Am to its hexavalent state in the presence of lacunary poly-anionic ligands have been carried out. The main results of several laboratory scale tests of the SESAME process are presented and the further process development is discussed. (author)

[en] The separation of long-lived radionuclides (LLRs) from nuclear wastes before conditioning and disposal will possibly lead to more economical and safer waste management in the future and has received the attention among the OECD Member countries. The workshop on 'Long-lived radionuclide chemistry in nuclear waste treatment' organised by CEA was held on 18-20 June 1997 at Villeneuve-les-Avignon, with 82 participants from the European Commission and 11 countries including the Czech Republic, France, Germany, Italy, Japan, Netherlands, Russia, Spain, Sweden, UK and USA. Twenty-three presentations were carried out in four sessions: Radioactive waste inventory, long-lived radionuclide contents, nature of the problems; Speciation of long-lived radionuclides; Thermodynamic properties of long-lived radionuclides relevant to their separation; Separation methods of long-lived radionuclides. (R.P.)

[en] At the Japan Atomic Energy Research Institute (JAERI), a partitioning process has been developed for the separation of elements in a high-level liquid waste (HLLW) into four groups: transuranium elements (TRU), Tc-platinum group metals (PGM), Sr-Cs and the others. The latest results are presented in the development of the four-group partitioning process at JAERI. Three subjects are described: basic data on the extraction of TRU with di-iso-decyl-phosphoric acid (DIDPA), partitioning test with simulated HLLW at the Nuclear Fuel Cycle Safety Engineering Research Facility (NUCEF) and preliminary assessment study on the four-group partitioning process. (author)