Volume 92, Issue 8 -

Excitation functions were measured by the stacked-foil technique for the reactions 85 Rb( p , pxn ) 84m, g,83, 82m, 81 Rb from their thresholds up to 100 MeV. Nuclear model calculations were performed using the code ALICE-IPPE both on ( p , xn ) reactions reported earlier and ( p , pxn ) reactions described here. The experimental excitation curves and the results of nuclear model calculations were found to be qualitatively in agreement. With the exception of the ( p , n ) reaction above 40 MeV, the theory appears to reproduce all the experimental data within deviations of about 50 %. The cross section ratios for the isomeric pairs 85m,g Sr and 84m,g Rb are discussed qualitatively in terms of the spins of the states involved and the increasing projectile energy.

Fully relativistic density-functional calculations of the electronic structures of various oxo-fluoro-complexes were performed for group-6 elements Mo, W, and element 106, Sg. Based on the electronic density distribution data, relative values of the free energy change of complex formation reactions in HF solutions have been defined. On their basis, sequences in the sorption of Mo, W, and Sg by an anion exchange resin ( K d values) have been predicted. The results show a complex situation depending on the acid concentration and pH of the solution. The predicted trends are in agreement with the known data for Mo and W. The following sequence in the sorption of Mo, W, and Sg by an anion exchange resin from 5×10 -3 HF/0.1 M HNO 3 solutions is predicted: Mo>Sg>W. A very good separation of Sg from Mo and W is expected at concentrated HF solutions, where MOF 5 - is formed. The sequence of the sorption in this case should be Sg ≫W > Mo.

By using an extractant, N,N,N´,N´-tetraoctyl-3-oxapentanediamide (TODGA), extraction and separation of Sr(II) from Am(III) were investigated for the partitioning of high level liquid waste (HLLW). Both metal ions, accompanied with the counter anion, NO 3 - , and HNO 3 without dissociation, were extracted by TODGA. We used two distinct methods for the separation of Am(III) and Sr(II). A mixture of TODGA and monoamide reduced the distribution ratio D of Sr(II) compared to that without monoamide, whereas D (Am) was still high value under the identical condition. After extraction of Am(III) by TODGA and monoamide, Sr(II) remaining in HLLW can be extracted by using enough concentration of TODGA at the next step. In the other method, Sr(II) was coextracted with Am(III) by TODGA. It was observed that D (Sr) decreased with an increase of HNO 3 from 3 M to 6 M HNO 3 at the same TODGA concentration, while D (Am) increased until 6 M HNO 3 . By using 6 M HNO 3 , Am(III) and Sr(II) were separated after coextraction.

A method was developed to determine activities and isotope ratios of plutonium and uranium. The method includes dry and wet ashing of air filters and separation of plutonium and uranium from each other and from other nuclides on Eichrom ® ´s extraction chromatography resins UTEVA and TRU. Interferences in plutonium separation caused by thorium and polonium were investigated and eliminated. A field trial was performed in Kurchatov, Kazakhstan, to test the aerosol sampling and radiochemical methods developed for plutonium and uranium. In the air samples collected, the activity of 239,240 Pu varied between 0.67 and 228 Bq/kg of dust, the activity of 238 Pu from 0.20 Bq/kg to 16.4 Bq/kg of dust, and the isotopic ratio 238 Pu/ 239,240 Pu between 0.011 and 2.4. Concentrations of Pu isotopes in the air were 13.4-2490 nBq/m 3 for 239,240 Pu and 7.2-960 nBq/m 3 for 238 Pu. Radioactivity of 239,240 Pu in air filters from Astana varied between 0.075 and 0.72 Bq per kg of dust and that of 238 Pu between 0.038 and 0.14 Bq/kg of dust. Activity concentration of 239,240 Pu in the air of Astana was 5.0-130 nBq/m 3 .

In the present work the performance of several processes used for advanced reprocessing of commercial LWR fuels as well as transmutation targets is compared. As a first step uranium and plutonium were recovered by PUREX type reprocessing. The raffinate, containing fission products including lanthanides and the minor actinides (MA) was used as feed for the second step in which minor actinides and lanthanides were separated from the bulk of the fission products. The five different processes tested use CMPO, DIDPA, TRPO, Diamide and CYANEX 923 as extractants. In the third step MA are separated from lanthanides. Here three processes were tested, i.e. using CYANEX 301, the synergistic mixture of di-chloro substituted CYANEX 301 and TOPO, and BTP solvents. Column-, batch- and continuous counter-current extraction techniques were used for the tests. The different processes will be described and discussed in terms of performances and efficiencies for Am and Cm separation. Efficient separation of MA from different genuine fuel solutions could be demonstrated and thereby also the possibility of closing a future transmutation fuel cycle. The combination of Diamide and BTP seems to be the best, among extractants tested, to achieve an efficient MA recovery from spent fuel.

We determined the association of uranium with bacteria isolated from the Waste Isolation Pilot Plant (WIPP), Carlsbad, New Mexico, and compared this with known strains of halophilic and non-halophilic bacteria and archaea. Examination of the cultures by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) showed uranium accumulation extracellularly and/or intracellularly to a varying degree. In Pseudomonas fluorescens and Bacillus subtilis uranium was associated with the cell surface and in the latter it was present as irregularly shaped grains. In Halobacterium halobium , the only archeon studied here, uranium was present as dense deposits and with Haloanaerobium praevalens as spikey deposits. Halomonas sp . isolated from the WIPP site accumulated uranium both extracellularly on the cell surface and intracellularly as electron-dense discrete granules. Extended X-ray absorption fine structure (EXAFS) analysis of uranium with the halophilic and non-halophilic bacteria and archaea showed that the uranium present in whole cells was bonded to an average of 2.4±0.7 phosphoryl groups at a distance of 3.65±0.03 Å. Comparison of whole cells of Halomonas sp . with the cell wall fragments of lysed cells showed the presence of a uranium bidentate complex at 2.91±0.03 Å with the carboxylate group on the cell wall, and uranyl hydroxide with U-U interaction at 3.71±0.03 Å due to adsorption or precipitation reactions; no U-P interaction was observed. Addition of uranium to the cell lysate of Halomonas sp . resulted in the precipitation of uranium due to the inorganic phosphate produced by the cells. These results show that the phosphates released from bacteria bind a significant amount of uranium. However, the bacterially immobilized uranium was readily solubilized by bicarbonate with concurrent release of phosphate into solution.

The uranyl/periodate system was investigated by Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLIFS), and Capillary Electrophoresis (CE) in 0.1 and 0.05 mol L -1 perchloric solutions at pH 2.6, containing various amounts of periodate anions. The formation of only one complex, UO 2 IO 4 + , was observed for a periodate concentration ranging from 5×10 -5 to 10 -1 mol L -1 . The stability constant of this complex was estimated to be log β 11 =1.8±0.2 by TRLIFS (fluorescence titration) and log β 11 =2.0±0.2 by CE, for an ionic strength of 10 -1 and 5×10 -2 mol L -1 , respectively. Moreover, the 1:1 stoichiometrical ratio between uranium(VI) and periodate was confirmed by an analysis of the results obtained from the deconvolution of fluorescence spectra.

The hydration number of lanthanides, Ln(III) (Ln = Sm, Eu, Tb, Dy), and Cm(III) in the extracted complexes with purified Cyanex301, Cyanex302 and Cyanex272 was investigated using time-resolved laser-induced fluorescence spectroscopy (TRLFS) and FT-IR spectroscopy. The results, in conjunction with the previous results on the Ln(III) and Am(III) complexes, provide insight into the composition of the extracted complexes. No difference has been observed in the hydration number or the composition between the Ln(III) and Cm(III) complexes with Cyanex302 or Cyanex272. The extracted complexes of Ln(III) and Cm(III) with Cyanex302 have the formula, ML(HL 2 ) 2 · n H 2 O, where L stands for the anion of Cyanex302 and n =3-5. No water molecules are found in the first coordination shell of Ln(III) or Cm(III) complexes with Cyanex272. In contrast to the extraction with Cyanex302 or Cyanex272, the composition of the Ln(III) complexes is different from that of the Cm(III) complex in the extraction with Cyanex301. The Ln(III) complex with Cyanex301 has one or two H 2 O molecules with a molecular formula of LnL 3 ·2H 2 O or HLnL 4 ·H 2 O, where L stands for the anion of Cyanex301. However, the Cm(III) complex with Cyanex301 does not contain H 2 O with the molecular formula of HCmL 4 , in which only the 8 sulfur atoms from Cyanex301 coordinate to Cm(III). The results for Cm(III) agree with the previous data for Am(III) from EXAFS and IR measurements.

Complexes of uranium(VI) and thorium(IV) with o-hydroxy N,N´-dimethylbenzylamine and o-carboxy N,N´-dimethylbenzylamine have been synthesized and characterized by elemental analysis, IR and 1 H-NMR techniques. The coordination of metal ions with the ligand and their structures were established. The chemical and spectral properties revealed that uranium(VI) complexes have square bipyramidal structure for coordination number 6, and hexagonal bipyramidal structure for coordination number 8, whereas thorium(IV) shows bicapped square antiprism structure for coordination number 10.

Ion exchange properties of cesium, strontium and europium on uranium antimonate (USb) from nitric acid medium was studied. The distribution coefficient ( K d ) of 1046 mL/g for cesium, 2464 mL/g for strontium and ∼10 5 mL/g for europium were obtained for sorption from 0.01 M nitric acid and K d decreased with increase in the concentration of nitric acid. Rapid sorption of metal ions in the initial stages of equilibration followed by the establishment of equilibrium after 24 hours. Cesium sorption on USb follows ideal ion exchange while strontium and europium do not. From Langmuir adsorption model for the sorption of these ions on USb, the apparent sorption capacity was found to be of 6.9 mg/g for cesium, 19.1 mg/g for strontium and 37.2 mg/g for europium at 300 K. The enthalpy change (Δ H °) accompanied by the sorption was determined by the temperature variation method. The performance of the sorbent under dynamic conditions was assessed by following a breakthrough (BT) curve up to C / C 0 =1. Extraction chromatography of individual ions from the mixture using USb was also reported in this paper.

The adsorption enthalpy of silver and gold atoms on fused silica surfaces was measured using vacuum-thermochromatography. Carrier-free silver, gold and platinum nuclides were produced by irradiation of cadmium, lead and mercury targets at the Swiss Spallation Neutron Source SINQ, followed by a thermochromatographic separation. For the calculation of the adsorption enthalpy from experimental data a thermodynamic model and a kinetic model (Monte Carlo simulation) were used. Our measurements revealed an adsorption enthalpy of -279±10 kJ/mol for gold, -232±13 kJ/mol for silver and an upper limit of -430 kJ/mol for platinum. These values, determined by the thermodynamic model, are in good agreement with literature values based on the same model. Additionally, Monte Carlo simulations have been performed to demonstrate the influence of temperature and size of quartz columns on the transport of model-isotopes with different half-lives.