Band 94, Heft 5 -

The release of iodine from liquid eutectic lead-bismuth alloy (LBE) under a flowing Ar/7%H 2 atmosphere has been studied in a temperature range from 428 to 1223 K using γ-ray spectroscopy. During short-term experiments, significant amounts of iodine evaporate from liquid LBE at temperatures higher than 800 K. Long-term experiments reveal that the release of iodine at temperatures of relevance to technical applications, such as liquid metal spallation targets or Accelerator Driven Systems (ADS), is below our detection limits for periods up to 7 days. The release rate is determined by the desorption/evaporation process rather than by diffusion within the liquid alloy.

The pH dependent sorption of Cm(III) onto alkali Feldspars (albite and orthoclase) is investigated by time resolved laser fluorescence spectroscopy (TRLFS) in the pH range from 3.4 to 9.4. Three single components are calculated from the raw spectra for both feldspar systems. The first component which corresponds to the Cm(III) aquo ion has a peak maximum at 593.8 nm and a fluorescence emission lifetime of 68±4 μs. This lifetime corresponds to a Cm(III) coordination of nine water molecules in the first coordination sphere of the actinide ion. The second component with a peak maximum at 601.4 nm corresponds to an adsorbed species. Its lifetime of 107±3 μs indicates a reduction of coordinating H 2 O/OH − ligands from nine to five caused by inner-sphere complex formation. The third component (603.6 nm) can be attributed to another sorption species. The corresponding lifetime is again 107±3 μs. Hence the number of coordinating ligands remains constant while the ligand field changes caused by the hydrolysis of the sorbed Cm(III). In a further set of experiments the Cm(III) sorption onto albite which is altered at pH 6.0 and pH 9.0 is also investigated by TRLFS. Independent of the dissolution and different surface morphologies caused by the alteration process the same Cm(III) species are formed as found for the sorption onto the untreated albite surface. With regard to the clarification of a feldspar dissolution mechanism the TRLFS results of the Cm(III) sorption onto altered feldspar surfaces give no evidence for a dissolution-reprecipitation based alteration mechanism.

X-ray absorption fine structure (XAFS) spectroscopy has been used to determine the speciation of Pu precipitates prepared by the heterogeneous reduction of Pu(VI) with Al and Fe in 5 M NaCl and an ERDA-6 brine, a simulant from the Waste Isolation Pilot Plant in Carlsbad, New Mexico. NaOCl was added to some of these solutions to determine its effect on Pu speciation. Analysis of the Pu L III spectra showed that all solids consisted of PuO 2+x-y (OH) 2y · z H 2 O, compounds with characteristics identical to those prepared by hydrolysis and with Pu-O and Pu-Pu distances identical to those treated at elevated temperature. Additionally, reduction with Al gave compounds with different site distributions than reduction with Fe, and reduction with Al or the addition of NaOCl appeared to suppress the formation of oxo groups and their associated Pu(V) sites.

The separation of trivalent actinides from the lanthanides using the active extractant in the Cyanex 301 reagent, bis(2,4,4-trimethylpentyl)dithiophosphinic acid, was studied. Specifically, the extractant was studied with an ammonium acetate/acetic acid buffered feed that would result from a transuranic separation process utilizing an ammonium acetate strip solution. Separation factors of 241 Am from 154 Eu with this extractant, as a function of total acetate concentration and pH, have been measured. Additionally, the extraction behavior of stable La, Ce, Pr, Nd, Sm and Eu was measured. Separation factors were typically very high for Am from Eu at a pH ranging from 3.8 to 5.8 and a total acetate concentration ranging from 0.2 M to 1.0 M. However, separation factors across the lanthanide series varied considerably and resulted in separation of the lighter lanthanides from the heavier lanthanides at the higher pH′s.

N , N ′-dimethyl- N , N ′-dibutyl tetradecyl malonamide (DMDBTDMA) coated magnetic particles are being evaluated for the possible application in the partitioning of actinides, lanthanides and fission products from pure nitric acid solutions as well as from Simulated Pressurized Heavy Water Reactor-High Level Waste (PHWR-SHLW). Uptake profiles of various metal ions, such as Pu(IV), U(VI), Am(III), Eu(III), Sr(II) and Cs(I) were obtained as a function of time and nitric acid concentration by batch studies using DMDBTDMA coated magnetic particles. The order of uptake follows the order Pu(IV)>U(VI)>Am(III)>Eu(III)>Sr(II)∼Cs(I) in both nitric acid and SHLW. The uptake of various trivalent lanthanides was also investigated as a function of nitric acid concentration and found the uptake order as Pr(III)>La(III)>Eu(III)>Tb(III)>Ho(III)>Er(III)>Yb(III)>Lu(III). The sorption capacity of the DMDBTDMA coated magnetic particles with respect to U(VI) and Eu(III) was determined, along with the sorption isotherms to simulate multiple contacts. The maximum sorption capacity of DMDBTDMA coated magnetic particles was found to be 1.58 mmol/g and 0.36 mmol/g for U(VI) and Eu(III), respectively. The adsorption models of Langmuir and Freundlich were fitted to the experimental data and best correlations were obtained for both the models. The Langmuir model predicts a loading capacity of 1.61 mmol/g and 0.37 mmol/g for U(VI) and Eu(III), respectively, which is close to the experimental values. The stability and recycling capacity of the DMDBTDMA coated magnetic particles was also assessed.

In the case of a rapid photochemical process, a new theoretical result relating time-resolved emission spectroscopy data to three physical parameters of the chemical system has been recently proposed. This previous work, based on a simulation study, is experimentally evidenced in the present paper, using europium/acetate as a model system. The comparison of the emission spectra obtained upon direct excitation of europium (394 nm) and by use of the “antenna effect” (266 nm) evidences the occurring of a back-dissociation of excited europium complexes to form solvated excited free europium ions.

A spectro-electrochemical cell was developed in order to study the speciation of radio-elements in thermodynamic unstable redox states using in situ XAS spectroscopy. This cell was used for the speciation of Re and Tc complexes in chloride media. Experiments on Re were carried out with the aim to validate the functionality of the experimental set-up. During electro-reduction of Re(VII) in HCl media, EXAFS and XANES studies were performed in order to reveal the formation of chloro-oxygenated compounds of Re(IV). The speciation of technetium in aqueous solutions of deep geological deposits for radioactive waste is important to predict its mobility under reducing conditions. XANES spectra showed that electro-reduction of Tc(VII) in chloride media leads to a position of K -edge absorption which agrees with a Tc(IV)/Tc(III) mixture.

The condensation mechanisms of tetravalent technetium in chloride media were studied in the pH range 0–1.5. A new dimer complex of Tc(IV) has thus been discovered, Tc 2 OCl 10 4− . Spectroscopic and kinetics studies showed that the formation of this compound resulted from the condensation of TcCl 5 (H 2 O) − . An EXAFS study indicates that the dimer displays a [Tc-O-Tc] 6+ structure. As the pH increases, UV-visible measurements showed a cyclization of [Tc-O-Tc] 6+ into [Tc(μO) 2 Tc] 4+ leading, in fine, to the precipitation of TcO 2 · x H 2 O. The aquation constant ( K aq ) of TcCl 6 2− into TcCl 5 (H 2 O) − and the dimerisation constant (log K dim ) of TcCl 5 (H 2 O) − into Tc 2 OCl 10 4− were determined to be 2.20±0.26 and 4.68±0.09, respectively.