Volume 93, Issue 5 -

The purpose of this study was to develop an optimised sample preparation method for the determination of Pu, Am, and Cm in environmental samples, soils, and sediments, and to compare the sensitivities of DF-ICP-MS, alpha spectrometry, and liquid scintillation alpha spectrometry. Borate fusion was used for sample material digestion. Two methods based on TOPO liquid–liquid extraction and combination of TEVA and TRU extraction chromatography showed highest yields of 92.7% for Pu, 86.8% for Am, and 87.6% for Cm. The detection limits were between 0.014–0.034 Bq/kg for 239 Pu, 0.014–0.093 Bq/kg for 240 Pu, and 0.011–1.20 Bq/kg for 241 Am. Analytical results for 238 Pu, 239 Pu, 240 Pu, 241 Pu and 241 Am and their isotope ratios in certified reference materials (IAEA-135 and IAEA-300) indicated very good accuracy of the methods proposed.

A comparative evaluation of 238 Pu determination in NIST-SRM-947-Pu isotopic reference material by alpha spectrometry and thermal ionization mass spectrometry (TIMS) is presented. Electrodeposited sources with geometric progression (G.P.) method to account for tail contribution were used in alpha spectrometry. In TIMS, the recently developed approach of using 235 U as a monitor isotope in interfering element correction methodology was employed to account for the isobaric interference of 238 U at 238 Pu. The atom % abundance of 238 Pu determined by both the methods is in good agreement with each other but is higher than that quoted by NIST in the reference material SRM-947-Pu.

The uranium(VI) silicate phases uranophane, Ca[(UO 2 )(SiO 3 OH)] 2 ·5H 2 O, and sodium boltwoodite, Na[(UO 2 )(SiO 3 OH)]·1.5H 2 O, were synthesized in the presence of small, variable quantities (0.5–2.0 mol % relative to U) of pentavalent neptunium (Np(V), as NpO 2 + ), to investigate the nature of its association with these U(VI) solid phases. Solids were characterized by X-ray powder diffraction (XRD), gamma spectrometry (GS), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) with electron energy-loss spectroscopy (EELS). Neptunium concentration was determined in the bulk solid phases by GS and was found to range from 780–15800 μg/g. In some cases, Np distributions between the aqueous and solid phases were monitored, and 78–97% of the initial Np was associated with the isolated solid. Characterization of individual crystallites by TEM/EELS suggests the Np is associated with the U(VI) phase. No discrete Np phases, such as Np oxides, were observed. Because the U(VI) silicates are believed to be important solubility-controlling solids on a geologic timescale, these results suggest that the partitioning of the minor actinides to these solids must be considered when assessing the performance of a waste repository for spent nuclear fuel.

Diffusion and sorption of U(VI) in compacted bentonite were studied using a capillary method. The experiments were carried out at room temperature in 0.1 M NaClO 4 solutions at pH 7.0±0.1. Effects of contact time, solution concentration and bentonite bulk density on diffusion were also investigated. The results fit the Fick's second law very well and are in good agreement with the literature data for similar bentonite dry densities [3]. The K d values from capillary method are in most cases lower than those from batch experiments. The interlaminary space of the compacted bentonite contributes significantly to the sorption of uranium. The apparent diffusion coefficient D a of diffusion derived from the experiments are used to simulate its diffusion in compacted bentonite and the results indicate that several meters of compacted bentonite is enough to prevent the diffusion of from the repository to the environment.

Two new ammonium uranyl oxalates (NH 4 ) 2 -[UO 2 (C 2 O 4 ) 2 H 2 O]·2H 2 O (1) and (NH 4 ) 2 [(UO 2 ) 2 (C 2 O 4 ) 3 ]· 3H 2 O (2) and one mixed ammonium hydrazinium uranyl oxalate (NH 4 )(N 2 H 5 )[(UO 2 ) 2 (C 2 O 4 ) 3 ]·3H 2 O (3) have been prepared. The crystal structures of the three compounds have been determined by single-crystal X-ray diffraction. The crystal structures were solved by the Patterson method and Fourier difference techniques, and refined by a least square method on the basis of F 2 for all unique reflections. Crystallographic data: 1, hexagonal, space group P6 1 22, a =8.143(2) Å, c =36.179(18) Å, Z =6, R 1= 0.0268 for 105 parameters with 1223 reflections with I ≥ 2σ( I ); 2, monoclinic, space group P 2 1 / n , a =8.705(3) Å, b = 19.454(6) Å, c =5.5105(18) Å, β=101.741(5)°, Z =2, R 1= 0.0314 for 139 parameters with 2059 reflections with I ≥ 2σ( I ); 3, monoclinic, space group P 2 1 / n , a =8.958(3) Å, b =19.601(7) Å, c = 11.007(4) Å, β=112.928(5)°, Z =4, R 1=0.0363 for 131 parameters with 3346 reflections with I ≥ 2σ( I ). The crystal structure of 1 contains [UO 2 (C 2 O 4 ) 2 · H 2 O] 2− anions, NH 4 + cations and water molecules. In the anion, the linear uranyl group is coordinated by two bidentate oxalate anions and one water molecule giving a pentagonal bipyramidal environment for the uranium atom. The structures of 2 and 3 consist of two-dimensional networks built from uranyl and oxalate ions forming hexagonal rings. The oxalate ions are tetradentate, each bridging two uranyl ions which are coordinated by three oxalate groups to give distorted hexagonal bipyramidal environments for the uranium atoms. In 3, the ammonium and hydrazinium ions are ordered in successive layers. The various possible coordinations for the uranyl cation and the great versatility of the oxalate anion are magnificently illustrated in the monovalent ion-uranyl double oxalates series and other structures are expected by the diversification of the synthesis methods and experimental conditions.

A number of structurally related new unsymmetrical monoamides with different substituting groups, N-methyl-N-decyloctylamide (MDOA), N-methyl-N-decyldecanamide (MDDA), and N-methyl-N-decyldodecanamide (MDDOA), were synthesized. The extraction of U(VI) from nitric acid medium by the synthesized monoamides diluted with toluene was investigated. The effect of nitric acid concentration, sodium nitrate concentration, extractant concentration and temperature on the distribution ratio was studied. The stoichiometry of the main extracted species confirms to UO 2 (NO 3 ) 2 ·2A (A, amidic extractant). The values of the thermodynamic parameters were determined and the extraction reactions were found exothermic. The IR spectral study was also made of the extracted species.

The distribution of 210 Po and 210 Pb in various particle-size fractions in Finnish groundwater was studied at five private homes. Each site had water treatment equipment comprising either an ion exchange unit or a granular activated carbon filter. Samples of both raw and treated water were filtered using pore sizes ranging from 450 nm to 100 kDa and the activity concentration of 210 Po and 210 Pb in the filtrate was determined. In untreated groundwater 86% of 210 Pb, on average, was found in the large particle fraction (>450 nm). However, in Fe- and Mn-rich water with a high Fe/Mn ratio and in organic-rich water, the majority of 210 Pb was found in either the intermediate particle (100 kDa–450 nm) or small particle (<100 kDa) fractions. Compared to 210 Pb, 210 Po was bound more to the intermediate and small particle fraction. After water treatment, 210 Pb was found most frequently in the large particle fraction. The size distribution of particle-bound 210 Po was not as clear as that for 210 Pb, and in treated water, 210 Po was more evenly distributed among fractions. The ion exchange unit removed 210 Pb and 210 Po bound to the intermediate or small particle fraction, whereas the efficiency of the activated carbon filters in removing 210 Pb and 210 Po was independent of the particle size.

In this paper, the transport and speciation of ruthenium under conditions simulating an air ingress accident was studied. Ruthenium dioxide was exposed to an oxidising environment at high temperatures (>1200 °C) in a tubular flow furnace. At these conditions, volatile ruthenium species were formed. A major part of the released ruthenium was deposited in the tube as RuO 2 . Depending on the experimental conditions, 12–35 wt. % of the released ruthenium was trapped in the outlet filter as RuO 2 particles. At completely dry conditions using stainless steel tubes, only 0.1–0.2 wt. % of the released ruthenium reached the trapping bottle as gaseous RuO 4 . However, when alumina was applied as tube material or the atmosphere contained some water vapour and silver seed particles, the fraction of gaseous ruthenium reaching the trapping bottle increased to 5 wt. % which is close to thermodynamic equilibrium. This indicates that RuO 2 does not catalyse the decomposition of RuO 4 .

A method for speciation of Tc(IV) species (TcCl 6 2− and TcCl 5 (H 2 O) − ) in chloride solutions, using capillary electrophoresis (CE) technique was developed. The proposed method has overcome the difficulties of unstable oxidation states analysis by shortening their travel time in the capillary. TcCl 6 2− and TcCl 5 (H 2 O) − were thus separated without being hydrolyzed and polymerized, and their UV/Vis spectra were recorded. With a 1 M HCl/NaCl buffer solution (pH=1), the electrophoretic mobilities were determined as 5.47×10 −4 cm 2 /Vs for TcCl 6 2− and 2.13×10 −4 cm 2 /Vs for TcCl 5 (H 2 O) − at 25 °C. The total analysis time for one run is 12 minutes.