Jan-Olov Liljenzin

Extraction properties of 6,6'-bis-(5,6-dipentyl-[1,2,4]triazin-3-yl)-[2,2']bipyridinyl (C5-BTBP)

Abstract The extraction of americium(III) and europium(III) into a variety of organic diluents by 6,6′‐bis‐(5,6,‐dipentyl‐[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridinyl (C5‐BTBP) has been investigated. In addition to determining the stoichiometry for the extraction, the dependence of extraction on contact time and temperature was also studied. The resistance of the ligand to gamma irradiation and the possibility to recycle the organic phase after stripping were tested to determine how the molecule would perform in a radiochemical process. Different organic diluents gave different extraction results, ranging from no extraction to distribution ratios of over 1000 for americium(III). In 1,1,2,2‐tetrachloroethane, the extraction and separation of americium from europium and the extraction kinetics were good; a separation factor above 60 was obtained at equilibrium, ∼5 min contact time. The extraction capabilities are adequate for C5‐BTBP to be used in a process for separating trivalent actinides from lanthanides. However, C5‐BTBP is susceptible to radiolysis (americium extraction decreases ∼80% after a dose of 17 kGy) and may not be the best choice in the processing of spent nuclear fuel. Nonetheless it is a useful starting point for further development of this type of molecule. It could also prove useful for analytical scale separations for which radiolytic instability is less important.

Separation of Actinides(III) from Lanthanides(III) in Simulated Nuclear Waste Streams using 6,6′‐Bis‐(5,6‐dipentyl‐[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridinyl (C5‐BTBP) in Cyclohexanone

Abstract An extraction system comprising 6,6′‐bis‐(5,6‐dipentyl‐[1,2,4]triazin‐3‐yl)‐[2,2′]bipyridinyl (C5‐BTBP) dissolved in cyclohexanone was investigated. The main purpose of this investigation was to extract and separate actinides(III) from lanthanides(III), both of which are present in the waste from the reprocessing of spent nuclear fuel. The system studied showed high distribution ratios for the actinides(III) and a high separation factor between actinides and lanthanides (SFAm/Eu around 150). The extraction kinetics were fast with equilibrium being reached in 5 minutes. The effects of temperature on the extraction and the stoichiometry of the extracted complex were investigated. The extraction of californium(III) was studied and it was found that the BTBP molecule has a higher affinity for californium than for americium (SFCf/Am around 4). This system could be used to separate actinides(III) from lanthanide fission products with high efficiency, if used in conjunction with a pre‐equilibrium step.

Recent achievements in the development of partitioning processes of minor actinides from nuclear wastes obtained in the frame of the Newpart European Programme (1996-1999)

Abstract Partitioning of long-lived minor actinides (americium and curium) from the nuclear wastes issuing the reprocessing of nuclear spent fuels, in order to transmute them into short-lived nuclides or to condition them into stable crystalline matrices, was the subject of intense research within the NEWPART research program of the European 4 th Frame Work Program, FWP (1996–1999). The target waste considered was the acidic raffinate (HAR) issuing the reprocessing of the used nuclear fuels by the PUREX process. A two step separation process based on liquid-liquid extraction was designed. The first step consists in the co-separation of the mixture of trivalent actinides and lanthanides from the HAR by extraction with a malonamide extractant (DIAMEX process), while the second step concerns the actinides(III)/lanthanides(III) group separation (SANEX process). Several DIAMEX and SANEX processes were developed and successfully tested with cold, spiked and genuine high active effluents. The research carried out also included basic and fundamental works in order to better understand the relationships between the structures of the extractants and their affinities for the target metal ions. The lecture highlighted both the basic and applied aspects of the research. This work will be pursued (PARTNEW program) within the 5 th FWP of the European Union during the period 2000–2003.

Assessment of uncertainty in parameter evaluation and prediction

Like in all experimental science, chemical data is affected by the limited precision of the measurement process. Quality control and traceability of experimental data require suitable approaches to express properly the degree of uncertainty. Noise and bias are nuisance effects reducing the information extractable from experimental data. However, because of the complexity of the numerical data evaluation in many chemical fields, often mean values from data analysis, e.g. multi-parametric curve fitting, are reported only. Relevant information on the interpretation limits, e.g. standard deviations or confidence limits, are either omitted or estimated. Modern techniques for handling of uncertainty in both parameter evaluation and prediction are strongly based on the calculation power of computers. Advantageously, computer-intensive methods like Monte Carlo resampling and Latin Hypercube sampling do not require sophisticated and often unavailable mathematical treatment. The statistical concepts are introduced. Applications of some computer-intensive statistical techniques to chemical problems are demonstrated.

HOT TEST OF A TALSPEAK PROCEDURE FOR SEPARATION OF ACTINIDES AND LANTHANIDES USING RECIRCULATING DTPA-LACTIC ACID SOLUTION

Results are reported from a hot test of a TALSPEAK type process for separation of higher actinides (Am, Cm) from lanthanides. Actinides and lanthanides are extracted by 1 M HDEHP and separated by selective strip of the actinides, using a mixture of DTPA and lactic acid (reversed TALSPEAK process). In order to minimize the generation of secondary waste, a procedure using recirculating DTPA-Lactic acid solution has been developed. A separation factor between Am and Eu of 132 was achieved. In regard to separations of Am and Cm from commercial HLLW (high level liquid wastes), the factor corresponds to 1.5% of the lanthanide group remaining with the actinides. The loss of Am was about 0.2%. 9 figures, 3 tables.

Determination of stability constants of lanthanide nitrate complex formation using a solvent extraction technique

Summary For lanthanides and actinides, nitrate complex formation is an important factor with respect to the reprocessing of nuclear fuels and in studies that treat partitioning and transmutation/conditioning. Different techniques, including microcalorimetry, various kinds of spectroscopy, ion-exchange and solvent extraction, can be used to determine stability constants of nitrate complex formation. However, it is uncommon that all lanthanides are studied at the same time, using the same experimental conditions and technique. The strengths of the complexes are different for lanthanides and actinides, a feature that may assist in the separation of the two groups. This paper deals with nitrate complex formation of lanthanides using a solvent extraction technique. Trace amounts of radioactive isotopes of lanthanides were produced at the TRIGA Mainz research reactor and at the Institutt for Energiteknikk in Kjeller, Norway (JEEP II reactor). The extraction of lanthanide ions into an organic phase consisting of 2,6-bis-(benzoxazolyl)-4-dodecyloxylpyridine, 2-bromodecanoic acid and tert-butyl benzene as a function of nitrate ion concentration in the aqueous phase was studied in order to estimate the stability constants of nitrate complex formation. When the nitrate ion concentration is increased in the aqueous phase, the nitrate complex formation starts to compete with the extraction of metal ions. Thus the stability constants of nitrate complex formation can be estimated by measuring the decrease in extraction and successive fitting of an appropriate model. Extraction curves for La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Dy, Ho and Er were obtained and stability constants for their nitrate complex formation were estimated. Tb, Tm, Yb and Lu were also investigated, but no stability constants could be determined. The distribution ratios for the metal ions at low nitrate ion concentration were obtained at the same time, showing the effect of lanthanide contraction resulting in decreasing extraction along the series. A clear tetrad effect in the lanthanide group was also found.

Solvent extraction of metal ions from nitric acid solution usingN,N′-substituted malonamides.Experimental and crystallographic evidence for two mechanisms ofextraction, metal complexation and ion-pair formation

The solvent extraction of actinides including Am III and Cm III together with some trivalent lanthanides from nitric acid solutions by two newly synthesized malonamides, N,N′-dimethyl-N,N′ -diphenyltetradecylmalonamide (dmptdma) and N,N′-dicyclohexyl-N,N′ -dimethyltetradecylmalonamide (dcmtdma) has been investigated and compared with data for the reference malonamide, N,N′-dibutyl-N,N′ -dimethyloctadecylmalonamide (dbmocma). The dependence of the extraction on the nitric acid and malonamide concentrations together with the probable molecular structure of the extraction species from nitric acid solution suggests that there are two principal mechanisms of extraction. For low nitric acid concentrations (up to 1 mol dm -3 ) a co-ordinative mechanism dominates for the extraction of metal cations, whereas at higher nitric acid concentrations (1–14 mol dm -3 ) an ion-pair mechanism involving the mono- or di-protonated malonamide and the metal anions [M(NO 3 ) 4 ] - or [M(NO 3 ) 5 ] 2- appears to be more important. Crystal structures show that in the protonated, unalkylated species Hdcmma + (dcmma = N,N′-dicyclohexyl-N ,N′-dimethylmalonamide) and in the chelated complexes [Nd(NO 3 ) 3 (dcmma) 2 ], [Nd(NO 3 ) 3 (H 2 O) 2 (dmpma)] and [Yb(NO 3 ) 3 (H 2 O)(dmpma)] (dmpma = N,N′-dimethyl-N ,N′-diphenylmalonamide) the carbonyl oxygens lie cis to each other suggesting that it is the cis form which is involved in extraction. However, crystal structures of the free unalkylated malonamides N,N′-dicyclohexyl-N,N′ -diethylmalonamide and N,N′-dicyclohexyl-N,N′ -diisopropylmalonamide show that the carbonyl amide groups adopt a trans configuration in which the carbonyl oxygens are at maximum separation. By contrast, in the crystal structure of the diphenyl derivative dmpma the carbonyl amide groups adopt a gauche configuration with an OC · · · C O torsion angle of 57.2°. Conformational analysis confirms that the differences in these structures reflect the differences between the lowest-energy gas-phase conformations and are not caused by packing effects.

COEXTRACTION OF URANIUM AND TECHNETIUM IN TBP-SYSTEMS

Abstract The coextraction of technetium with uranium in TBP/HNO systems has been studied. The extraction mechanism, has been found to agree well with experimental data at 5 M HNO,.The extraction constant, KTC,e for this reaction Is given by where T is temperature (K) and CT total TBP concentration (%). This equation is valid for 5 M HNO, DSFS–30% TBP, and from 20 to 60°C, with an average error of 2·8% in log KTC,e

Reducing the Long-Term Hazard of Reactor Waste Through Actinide Removal and Destruction in Nuclear Reactors

Abstract Public opposition to nuclear power has focused on the long-term risks from reactor waste. In the Purex process used in Europe, this waste is a concentrated nitric acid solution containing all nonvolatile fission products and the actinides Np, Am, and Cm, plus smaller amounts of U and Pu. Techniques have recently been described which guarantee an absolutely safe containment of this high-active waste (HAW) for about 1000 years. At longer times, the risk to the biosphere is dominated by the actinides. If these actinides are isolated from the rest of the HAW and destroyed through nuclear incineration, the long-term risks of the HAW will be dramatically reduced. This paper presents a detailed scheme for removing the actinides from the Purex-HAW solution. In principle, the process consists of three different solvent extraction cycles, using HDEHP and TBP in three successive steps. The scheme has been tested on a synthetic HAW solution containing all fission products and actinides (except Z ≥96, Cm) usi...

Analysis of the Fallout in Sweden from Chernobyl

By J. O. LILJENZIN, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindem, N-0315 Oslo 3, Norway M. SKALBERG, Department of Nuclear Chemistry, Chalmers University of Technology, S-412 96 Göteborg, Sweden G. PERSSON, T. INGEMANSSON, Swedish State Power Board, Forsmark Nuclear Power Plant, S-742 00 Osthammar, Sweden and P. O. ARONSSON, Swedish State Power Board, Ringhals Nuclear Power Plant, S-430 22 Väröbacka, Sweden