Volume 89, Issue 10 -

The separation of americium-241, curium-242/244, plutonium-238/239, neptunium-237, and uranium-234/235/238, in the same sample aliquot of clear acidic solution resulting from the electrometallurgical treatment of spent nuclear fuel has been investigated. Using ion exchange techniques in 10 M HCl media, it was determined that good separation can be achieved to resolve each isotope via alpha spectroscopy. The resin used was AG 1-x8 chloride form supplied by BioRad® Laboratories. The retention and eluting conditions for each isotope were determined using tracer techniques and will be presented. Based on this work, an analytical procedure for the sequential separation of Am, Cm, Pu, Np, and U, in various sample matrices recovered from the demonstration project is presented.

Samples of clean soil from the source used to backfill pits at the Idaho National Engineering and Environmental Laboratory´s Radioactive Waste Management Complex were spiked with 239 Pu and 241 Am to evaluate ligand-assisted supercritical fluid extraction as a decontamination method. The actual soil in the pits has been subject to approximately three decades of weathering since it was originally contaminated. No surrogate soil can perfectly simulate the real event, but actual contaminated soil was not available for research purposes. However, fractionation of Am and Pu in the surrogate soil was found to be similar to that previously measured in the real soil using a sequential aqueous extraction procedure. This suggests that Pu and Am behavior are similar in the two soils. The surrogate was subjected to supercritical carbon dioxide extraction, in the presence of the fluorinated beta diketone thenoyltrifluoroacetone (TTA), and tributylphosphate (TBP). As much as 69% of the Pu and 88% of the Am were removed from the soil using 3.2 mol.% TTA and 2.7 mol.% TBP, in a single 45 minute extraction. Extraction conditions employing a 5 mol.% ethanol modifier with 0.33 mol.% TTA and 0.27 mol.% TBP resulted in 66% Pu and 68% Am extracted. To our knowledge, this is the first report of the use of supercritical fluid extraction (SFE) for the removal of actinides from soil.

The extraction of carrier-free tungsten and molybdenum from nitric, phosphoric and sulphuric acid with 0.05 M TOA (tri- n -octyl amine, R 3 N) in toluene and 2.5% by volume 1-dodecanol has been studied. Their extraction behaviour has also been compared to hafnium, some trivalent lanthanides (lanthanum, cerium, thulium, ytterbium and lutetium) and some actinides (thorium, uranium, americium and curium). The extraction of these metal ions decreases in the order M 4+ >MO 2 2+ >M 3+ from >1 M nitric acid solutions, if hafnium, which is on the form HfO 2+ , is disregarded. At low nitric acid concentrations tungsten and molybdenum are most likely extracted as tungstate or molybdate ions (R 3 NH) 2 ·MO 4 , while at higher concentrations they are most likely extracted similar to uranium, i.e. on the form R 3 NH·MO 2 (NO 3 ) 3 . Further, the extraction from phosphoric acid solutions decreases in the order M 4+ >MO 2 2+ >M 3+ , if the elements which are easily hydrolysed, hafnium, molybdenum and tungsten, are disregarded. The major extracted complex of tungsten contains one TOA and the minor two TOA. The extracted complex with one TOA is probably (R 3 NH)·WO 2 (H 2 PO 4 ) 3 or R 3 N·WO 2 (H 2 PO 4 ) 2 , while that with two TOA more likely is (R 3 N) 2 H·WO 2 (H 2 PO 4 ) 3 or even the more hydrolysed species of tungsten (R 3 NH) 2 ·WO 4 . For molybdenum, the extracted complexes seem reasonably similar. Disregarding HfO 2+ the extraction decreases in the order MO 2 2+ >M 4+ >M 3+ for the chosen range of sulphuric acid concentration.

Uranium(VI) complex formation at vegetative cells and spores of Bacillus cereus and Bacillus sphaericus was studied using uranium L II -edge and L III -edge extended X-ray absorption fine structure (EXAFS) spectroscopy. A comparison of the measured equatorial U-O distances and other EXAFS structural parameters of uranyl species formed at the Bacillus strains with those of the uranyl structure family indicates that the uranium is predominantly bound as uranyl complexes with phosphoryl residues.

Several procedures of general application for the total dissolution of inorganic samples using a microwave oven were studied in detail. They were applied to the determination of thorium isotopes by alpha spectrometry. This study revealed the existence of various stages during the process of digestion that led to an apparent differential behaviour of the isotopes of thorium, so that the original isotopic composition of the sample was completely lost. We introduced changes in the dissolution procedures which resulted in good agreement between the experimentally determined and the true isotopic ratios.

The diffusion of 99 Tc in granite was investigated with small-sized diffusion cells, composed of a radioactive source solution cell and a sampling cell. Water in the two cells was kept at the same level. 1 ml aliquots were taken from the sampling cells daily during the first 50 days, then at intervals of several days, and measured via liquid scintillation counting. The experimental results indicate that the diffusion of 99 Tc and 3 H in granite follows the one-dimensional diffusion equation when diffusion time is long enough (>100 days). The calculated average diffusion coefficient of 99 Tc (1.4×10 -12 m 2 /s) is about one half of that of 3 H (3.2×10 -12 m 2 /s).

The migration of 99 Tc in unsaturated Chinese loess under artificial rainfall condition was investigated in situ . Water suckers were buried at different depths under the bottom of an experimental pit of 2 m × 2 m × 1 m (deep). Quartz containing 3 H and 99 Tc was introduced into the experimental pit to an area of 40 cm × 40 cm and the pit was backfilled to a thickness of 30 cm. An artificial rainfall of 5 mm/h was applied to the experimental pit 4 h a day for 3 months. Moisture water samples were sucked with the help of a vacuum pumping system and the activity of 3 H and 99 Tc in the samples was determined. Breakthrough curves of 3 H and 99 Tc indicated that 99 Tc was slightly retarded. The calculated average apparent distribution coefficient of 99 Tc in the medium was (1.98±0.42)×10 -2 ml/g.

Zirconium phosphate hase been prepared by solid-solid reaction. The characterization of this inorganic ion exchanger was done with respect to capacity, pH titration, dissolution, etc. The preconcentration and separation of fission products, Sr(II), Co(II), Eu(III), Gd(III), Hg(II) and Am(III) has been achieved from different acidic media, HCl, HNO 3 , H 2 SO 4 , HClO 4 . The speciation of these cations in different media has been investigated. From the results obtained, it is obvious that these cations can be preconcentrated in low acidic medium, whilst at high acidity in the range 1-2 M, they be can separated from each other.

The interaction between Ca 2+ and humic acids (HA) was studied at ionic strengths from 0.10 to 5.0 m (NaCl) by the solvent extraction technique. The dependence of the stability constants upon pcH (4.7 to 9.0) was interpreted by the polyelectrolyte model of HA. The data was consistent with formation of a single Ca-HA complex.

A method is described for the production of 223 Ra ( t 1/2 =11.4 d) in a quality useful for endoradiotherapeutic applications. The method is based on a long term operating generator with a source of 227 Ac ( t 1/2 =21.7 years), from which 223 Ra is eluted. The 227 Ac was isolated from a 231 Pa source using the f-element selective extraction chromatographic material TRU-resin. The purified 227 Ac/ 227 Th source was subsequently applied to another extraction chromatographic resin, containing the extractant P,P ′ -di(2-ethylhexyl)methanediphosphonic acid on silica (Dipex-2) and used as a generator for 223 Ra. From the generator column, the yield of 223 Ra was about 60 kBq per 100 kBq of 227 Ac with a highly effective separation of 223 Ra from the precursors. In production runs, the activity of 227 Ac was found to be 6×10 -6 relative to the eluted activity of 223 Ra. By using a second column of Dipex-2 for additional purification, the activity of Ac was reduced to below 7×10 -8 relative to 223 Ra with nearly quantitative recovery of 223 Ra. The described procedure resulted in a high purity 223 Ra preparation, potentially useful in, e.g ., targeted radiotherapy of tumors.