Volume 88, Issue 2 -

The interaction of americium(III) with aqueous silicic acid was studied by competitive solvent extraction with 0.1 M thenoyltrifluoroacetone (HTTA) as extractant. The aqueous phase contained only 0.2 M NaClO 4 or additionally 0.03 M silicic acid at p[H] 3.0-3.8 adjusted with perchloric acid. 241 Am was used in tracer amounts and its distribution ratio was measured γ -spectrometrically. Silicic acid solutions were prepared by hydrolysis of tetramethylorthosilicate (TMOS). Kinetic investigations with the molybdate reaction showed polymeric silica fractions between 10-17% within the p[H] range investigated. Extraction times of about 1.5 hours were taken to assure distribution equilibrium for the 241 Am extraction. The occurrence of a 1:1 complex of americium with silicic acid according to the reaction Am 3+ + Si(OH) 4 ↔ AmOSi(OH) 3 2+ + H + could be demonstrated and a formation constant of K 1 = (6.9±0.7)×10 -3 [log K 1 = -2.16±0.04] at I = 0.2 M was calculated.

The rate equations for the reduction of Np(V), Np(VI) and Pu(IV) ions by acetaldoxime in nitric acid have been determined as: -d[Np(V)]/dt = k 26 [Np(V)][CH 3 CHNOH][HNO 3 ] 1.2 - d[Np(VI)/dt = k 19 [Np(VI)][CH 3 CHNOH]/[HNO 3 ] - d[Pu(IV)/dt = k 6 [Pu(IV)] 2 [CH 3 CHNOH] 1.1 /[Pu(III)][HNO 3 ] 2.2 where respectively: k 26 = (9.2±0.2)×10 -4 l 2.2 mol -2.2 min -1 at 60° C; k 19 = 254±10 min -1 at 26.0° C; k 6 = 25.3±1.9 mol 1.1 l -1.1 min -1 at 19.5°C. The activation energies were found to be: E 19 = 62.6±2.6 kJmol -1 and E 26 = 87.7±9.8 kJmol -1 . Np(V) was generally found to be stable for long periods in nearly all the kinetic experiments and the reduction of Np(V) to Np(IV) could only be studied at elevated temperatures and reactant concentrations. Possible reaction mechanisms for the reduction of Np(VI) and Pu(IV) have been suggested; proceeding, in both cases, via the hydrolysis product and an intermediate CH 3 CHN¤O radical. Simple solvent extraction experiments have shown that Np(VI) and Pu(IV) can be reductively stripped from 30% TBP/n-dodecane in the presence of U(VI).

Accumulation studies with vegetative cells and spores of three Bacillus isolates (JG-A 30, JG-A 12, JG-A 22, classified as Bacillus cereus, Bacillus sphaericus, Bacillus megaterium) from a uranium mining waste pile (Johanngeorgenstadt, Saxony) and their corresponding reference strains have shown that Bacilli accumulate high amounts of U(VI) in the concentration range examined (11-214 mg/L). Information on the binding strength and the reversibility were obtained from extraction studies with different extractants. With 0.01 M EDTA solution the uranium bound to the biomass was released almost quantitatively. The characterization of the bacterial-UO 2 2+ -complexes by time-resolved laser fluorescence spectroscopy (TRLFS) showed the formation of inner-sphere complexes with phosphate groups of the biomass. The results lead to the conclusion that the cell wall components with phosphate residues e.g., polysaccharides, teichoic and teichuroic acids or phospholipide layers of the membranes are responsible for the uranium binding. The spectroscopic studies of the U(VI)-complexes with isolated bacterial cell walls and isolated surface-layer proteins of the strain Bacillus sphaericus NCTC 9602 after cell fractionation have shown that the complexation of U(VI) with intact cells (vegetative cells or spores) is different from the coordination with isolated cell wall components, especially with the S-layer proteins. For all Bacillus strains studied in this work, a significant contribution of the S-layer proteins to the binding of uranyl to living cells can be excluded.

The leaching of natural radionuclides from the material of a uranium mill tailing at Crossen/Saxony was investigated using eight columns (20 cm diameter, 50 cm height). Six columns were irrigated in the laboratory by synthetic rainwater of pH 6, 3 and 2, two columns were exposed outdoor to natural meteorological conditions. In the effluent of the columns, the concentrations of the radionuclides were measured periodically. With exception of the initial phase after installation of the columns (ca. 0.4 y), the leaching rates of radionuclides decreased slowly within the observation period of 4.5 years. Due to the buffering capacity of the tailings material, acidifying the irrigation water of the laboratory columns did not effect the effluent concentrations of the radionuclides. However, significant differences were observed between laboratory and outdoor columns: outdoor, the concentration of 235 U in the effluents was for the first two years substantially smaller than in the laboratory. As a consequence, the accumulated leached activity of 235U during 4.5 years was 19.0±0.9% of the inventory for the laboratory columns, but only 10.9±0.6% for the outdoor columns. While uranium thus proved to be rather soluble, the concentration of 226 Ra in the effluents was quite small (<1 Bq/l). Thorium was retained completely in the columns.

An analytical method for the determination of uranium enrichment in uranium oxide without using any calibration standards is described. Very good agreement between the measured and certified values was obtained in the analysis of a Standard Reference Material. Precise energies and emission probabilities were derived for two weak gamma-rays of 234m Pa: at 258.227±0.003 keV, (0.076±0.002)% and 742.813±0.005 keV, (0.106±0.002)%.

The chloride and oxychloride chemistry of the group 7 elements Tc and Re was investigated in order to develop an experimental approach to a gas chemical characterisation of bohrium (Bh, element 107). In thermochromatography experiments with trace amounts of 101,104 Tc and 183,184 Re the formation of one volatile compound was observed in O 2 /HCl containing carrier gas, which was attributed to MO 3 Cl (M = Tc, Re). From the measured deposition temperatures the adsorption enthalpies on quartz surfaces ΔH ads (TcO 3 Cl) = -51 ± 3 kJ/mol and ΔH ads (ReO 3 Cl) = -62 ± 3 kJ/mol were evaluated. The sublimation enthalpies were derived using an empirical correlation between Δ H ads and ΔH subl : ΔH subl (TcO 3 Cl) = 49±10 kJ/mol and ΔH subl (ReO 3 Cl) = 67±10 kJ/mol. A fast gas chemical separation technique for highly volatile compounds of short-lived isotopes based on isothermal gas solid adsorption chromatography (OLGA-principle) was developed. With a modified OLGA device, model studies with the short-lived nuclides 106,107,108 Tc and 169,170,174,176 Re were carried out in preparation of an experimental gas chemical investigation of bohrium (Bh, element 107). Separation times of less than 3 s were achieved. A good separation of the oxychlorides of group 7 elements from chloride and oxychloride compounds of 152-155 Er, 151-154 Ho (as models for actinide elements), 98-101 Nb, 99-102 Zr (as models for light transactinide elements), 218 Po, and 214 Bi was accomplished in this chemical system.

A natural moor soil humic acid (HA) was labeled with Tc-99m via reduction of pertechnetate with stannous chloride. The humic acid species obtained were characterized by thin layer chromatography (TLC), gel permeation chromatography (GPC), sequential chromatographic analysis (SCA), paper electrophoresis and micropore filtration. Labeling was found to take place in all ranges of molecular weight. Due to the complex humic acid composition and the formation of hydroxo species the labeling yields strongly depend on the separation conditions, ranging from 42% to 80%. The pH-dependent distribution of mobile and immobile species was determined by SCA for HTcO 4 , HA and for Tc-HA-species obtained after labeling. Geochemically relevant properties of HA remain unchanged after the labeling procedure, only macroscopic amounts of the reducing agent Sn 2+ give rise to a shift to lower molecular weight species.

The removal of some hazardous radioactive nuclides such as Cs + , Co 2+ , Sr 2+ and/or Eu 3+ from radioactive liquid waste was carried out either by chemical in-situ precipitation or by using a preformed precipitate of tin(IV) antimonate (SnSb). Stability of the product material for the chemical reagents was investigated at various concentrations of nitric and hydrochloric acids. Capacity and selectivity patterns for Cs + , Co 2+ , Sr 2+ and Eu 3+ were determined on these matrices. Conditioning of the exhausted tin(IV) antimonate in cement matrix was carried out with the study of some important parameters affecting the properties of the solidified waste forms such as, the compressive strength and the leaching coefficient of these nuclides from the solidified waste form. The leaching coefficient of radioactive nuclides precipitated in-situ with SnSb are smaller than those adsorbed on SnSb or plain ordinary portland cement.

Adsorption of Zn(II) ions on hydrous zirconium oxide was studied as a function of concentration of Zn(II), temperature and pH of the adsorptive solution using 65 Zn tracer and high resolution γ -ray spectroscopy. Kinetics of the adsorption for various initial concentration, [C0], of Zn(II) ion was studied. For [C 0 ] ≤ 10 -5 M, the adsorption process was found to obey the first order rate law. The activation energy for the adsorption of Zn(II) was determined to be 51.2 kJ/mol. Interaction of Zn 2+ ions with the adsorption sites is responsible for the adsorption of Zn(II) on hydrous zirconium oxide.

This work aims at analysis of radioactivity levels in the water of spent fuel pool and reactor core of the Egyptian 2MW research reactor (ET-RR.1 at Inshas). Gamma spectrometric and laser fluorimetric analysis have been used for carrying out this study. The fission product 137 Cs and activation product 60 Co are found with very high concentration in the spent fuel storage pool water. Thirteen isotopes; La-140, Cr-51, Ba-140, I-131, Cs-137, Ce-144, Nb-95, Ce-141, Zr-95, Ru-103, Cs-134, Nd-147 and Zn-65 are identified in the reactor core water. However no radiological hazard resulted because the fission products are contained within the shielded reactor pool. The radioactivity released into the reactor coolant water is mainly controlled by the diffusion mechanism.

Heavy ion activation of natural Sb 2 O 3 with 78 MeV 16 O 6+ results in the formation of carrier-free praseodymium isotopes, 133,135 Pr, and their corresponding decay products 133,135 Ce, in the matrix. Also irradiation with ~ 90 MeV 19 F 7+ beam leads to the production of carrier-free neodymium isotopes, 135-138 Nd, which decay out to 135-138 Ce via 135-138 Pr. Another way for the production of carrier-free 135 Ce radionuclide is to irradiate CsNO 3 target with 7 Li 3+ beam of energy 44 MeV. The shorter lived radionuclides of cerium decay out and a radiochemical procedure has been developed for the separation of carrier-free radionuclides from the bulk target matrix antimony and caesium through liquid-liquid extraction (LLX) using Aliquat 336 (tricaprylmethylammonium chloride), and di-(2-ethylhexyl)phosphoric acid (HDEHP) as extractants.