bluuebunny/crossref_metadata_2025 huggingface dataset:
The oxidation of hydroxylamine by nitric and nitrous acids in the presence of technetium (VII)
Authors: Koltunov V. S. , Taylor Robin J. , Gomonova T.V. , Savilova O. A. , Zhuravleva G.I. , Denniss I.S.
Published: August 2006

The oxidation of hydroxylamine by nitric acid in the presence of technetium ions at temperatures above ~60°C is an autocatalytic process comprising an induction period and then a catalysed reaction involving HNO2, which has accumulated in the solution. Tc ions have no appreciable effect on the reaction rate, which is governed only by the nitric and nitrous acid oxidation reactions of hydroxylamine, but the presence of Tc ions does extend the initial induction period. The rate of hydroxylamine oxidation by HNO3in the presence of HNO2, that is, after the induction period, was found to be:

-d[NH3OH+]/dt = k[NH3OH+][HNO2][HNO3]3.5

where k = 120±10 l4.5mol-4.5min-1at T = 80°C, μ = 2 and [H+] ≤ 2 M. Under these conditions, the reaction apparently has a high activation energy of 160-180 kJ mol-1. At low temperatures (20-40°C) hydroxylamine is effectively stable in solutions of HNO3up to concentrations of ~2 M, whether or not Tc(VII) ions are present. Tc(V) was also observed to form at least one complex on reduction with excess hydroxylamine with an absorption maximum between 467 and 480 nm dependent on the solution acidity.
Cross-sections and linear momentum transfer in α-induced reactions on 85Rb
Authors: Guin R. , Das S. K. , Saha S. K.
Published: August 2006

Cross-sections for the reactions 85Rb(α,2n)87Y, 85Rb(α,3n)86Y and 85Rb(α,αn)84Rb have been determined in the α-energy range of 20-50 MeV. Integral recoil ranges of the evaporation residue for the reaction 85Rb(α,αn)84Rb have also been measured. From the recoil range data, the linear momentum transfer to the product nucleus for the above reaction has been deduced. The experimental results are compared with theoretical model predictions. For (α,xn) reactions, the agreement between the theory and the experiment is found to be quite satisfactory. In case of (α,αn) reaction, the theoretical calculations fail to reproduce the experimental cross-sections as well as linear momentum transfer even when the incident α-energy is quite low.
Sorption and desorption kinetics of Np(V) on magnetite and hematite
Authors: Nakata K. , Nagasaki S. , Tanaka S. , Sakamoto Y. , Tanaka T. , Ogawa H.
Published: August 2006

Sorption kinetics of Np(V) on magnetite and hematite were investigated, and a sequential desorption method was applied to investigate changes in the chemical form of Np sorbed according to the amount of time they were in contact with the Np solution. It was found that the sorption process consists of fast sorption and slow sorption which reaches equilibrium in 1 h. According to the desorption results, it was conjectured (i) that fast sorption is attributable to sorption on/into the surface and non-crystalline phases of iron oxides for magnetite and hematite in both acidic and alkaline solutions, (ii) that sorption on/into the crystalline phase also contributes to fast sorption for hematite in an alkaline solution, and (iii) that slow sorption represents sorption into the crystalline phase of magnetite in both acidic and alkaline solutions and that of hematite in an acidic solution. From the results of sorption and desorption kinetics, it was concluded that the equilibrium between various chemical forms of sorbed Np was achieved in about 1 week, although the amount of sorbed Np reached an equilibrium in only 1 h.
Secondary ion mass spectrometry measurements of volcanic tuffs containing radionuclides from underground nuclear tests
Authors: Rose T.P. , Smith D.K. , Phinney D.L.
Published: August 2006

The in situ distribution of anthropogenic radionuclides in volcanic tuffs was measured using secondary ion mass spectrometry (SIMS). Samples were obtained from boreholes drilled in close proximity to expended underground nuclear test cavities at the Nevada Test Site, USA. SIMS measurements revealed the presence of22Na,137Cs, and enriched235U/238U ratios. The radionuclides are distributed heterogeneously and occur at concentrations ranging from 1 to <0.1 ppm. Two processes govern the distribution of radionuclides outside the nuclear test cavity region: the prompt injection of radionuclides along fractures at the time of the nuclear detonation, and the post-test sorption of radionuclides from groundwater. A zone of prompt injection 37 m above the static water table is characterized by the correlated presence of all three radionuclides - in one case, all within a single (60 μm) point of analysis.137Cs is the only radionuclide detected in rocks from the saturated zone. Since these volcanic tuffs are highly zeolitized, containing up to 60 wt % clinoptilolite, it is likely that zeolite minerals control137Cs sorption from groundwater. However, the heterogeneous distribution of radionuclides within the zeolitized samples indicates that micro-fractures in the rock are also important in determining where the radionuclides are deposited.
Experimental determination and chemical modelling of radiolytic processes at the spent fuel/water interface
Authors: Bruno J. , Cera E. , Eklund U.-B. , Eriksen T. , Grivé M. , Spahiu Kastriot
Published: August 2006

The spent fuel matrix constitutes a dynamic redox system, due to the time-dependent generation of oxidants and reductants at the spent fuel/water interface by alpha, beta and gamma radiolysis. In this context it is critical to understand the main processes and mechanisms that control the radiolytic production of redox components at this interface and their impact on the stability of the UO2 matrix and in radionuclide release.

In order to achieve this, a series of carefully controlled experiments have been carried out in order to determine the time dependence of the radiolytic H2, O2 and H2O2 production and radionuclide release (U, Pu, Np, Tc, Mo, Sr and Cs). These tests have been performed by using PWR Ringhals spent fuel fragments in contact with 10 mM NaHCO3 solutions in an initially anoxic and closed system.

The results of these experiments indicate quite a consistent and reproducible behaviour of the radiolytically generated reductants and oxidants. The results indicate that it is possible to define an equilibrium redox potential for the main redox pairs in the bulk system and that the experimentally determined radionuclide release can be rationalised in terms of the system redox potential.
Thermodynamic data for the solubility of tin(IV) in aqueous cementitious environments
Authors: Lothenbach B. , Ochs Michael , Hager D.
Published: August 2006

The solubility of Sn(IV) in cementitious systems is directly related to the presence of dissolved Ca. In the presence of typical Ca concentrations, solid Ca[Sn(OH)6](s) is precipitated, resulting in dissolved tin(IV) concentrations that are about four to six orders of magnitude lower than observed in alkaline, Ca-free systems. From different experiments carried out in initially oversaturated and undersaturated solutions, solubility products have been evaluated.

A constant of 109.85 at I=0 has been derived for the formation of fresh Ca[Sn(OH)6](precip) according to the reaction Ca2++{Sn(OH)6
2- ↔ Ca[Sn(OH)6](s). A constant of 1010.93 has been derived in undersaturation experiments for the equilibrium with crystalline Ca[Sn(OH)6](cr).
Leaching behaviour of UO2 containing α-emitting actinides
Authors: Rondinella V.V. , Matzke Hj. , Cobos Carlos J. , Wiss T.
Published: August 2006

After a few hundred years in a geologic repository, α-emissions will dominate the radiation field in and around spent nuclear fuel. In the event of a failure of the spent fuel container, the dissolution of the uranium dioxide matrix in contact with groundwater could be enhanced by α-radiolysis, which could create oxidizing conditions at the fuel surface. The radioactivity (hence the radiolysis) of the irradiated fuel available nowadays is characterized by strong β- and γ-contributions, which are not representative of aged fuel in a repository. A possible way to single out the effects of α-radiolysis on the dissolution behaviour of irradiated fuel is to study unirradiated UO2 doped with a short-lived α-emitter. UO2 containing ~0.1 and ~10 wt.% of 238PuO2 was fabricated and leached. Previous results of static (batch and sequential) leaching tests on monoliths at room temperature in demineralized water under anoxic atmosphere showed that the amounts of U released were higher in the case of UO2 containing 238Pu than in the case of undoped UO2. This work presents results of leaching experiments performed under similar conditions on materials of the same composition, but crushed to give samples with two different particle size distributions to investigate the effects of different surface areas. The U release data, normalized to the geometric surface area, showed enhanced U dissolution from α-doped UO2 also in the case of crushed materials, except for the initial release after 1 h of leaching. Under these experimental conditions, the concentration of U measured in the leachates for the two doped materials did not show a clear dependence on α-activity.
Aqueous dissolution kinetics of pyrochlore, zirconolite and brannerite at 25, 50, and 75 °C
Authors: Roberts S. K. , Bourcier W.L. , Shaw H.F.
Published: August 2006

We measured the rates of dissolution of pyrochlore, zirconolite, and brannerite in pH-buffered solutions of pH 2, 4, 6, 8, 10, and 12 at temperatures of 25, 50, and 75 °C in flow-through reactors. The dissolution rates for all phases show a minimum near pH 8. Zirconolite dissolves the slowest of the three phases, with a slightly higher rate for pyrochlore and a much higher dissolution rate for brannerite. Brannerite dissolves as much has 30 times faster than zirconolite. The rates increase with temperature, but the magnitude of the increase varies with pH. The calculated average apparent activation energy for dissolution is 6±3 kcal/mole. Dissolution is non-stoichiometric at all pHs. Ti and Hf are released most slowly, and are often below detection limits (1 ppb for Ti, 0.2 ppb for Hf). Releases of Ca, U, Gd, and Ce appear to be stoichiometric below pH 8. At pH 8 and above only U is measurable in solution. Dissolution rates are slow under all conditions, and commonly in the range of 1-100 nm total dissolution/year (between 10-3.5 and 10-5.5 g/m2/day).
Investigation of humic acid complexation behavior with uranyl ions using modified synthetic and natural humic acids
Authors: Pompe S. , Schmeide K. , Bubner M. , Geipel Gerhard , Heise K. H. , Bernhard G. , Nitsche Heino
Published: August 2006

We investigated the influence of phenolic OH groups on the complexation behavior of humic acid (HA) with UO22+ions at pH 4. Starting from synthetic HA type M1, natural HA Aldrich, and natural HA Kranichsee, we synthesized modified HAs with blocked phenolic OH groups by derivatization with diazomethane. The partial blocking of phenolic OH groups was confirmed by a radiometric method which quantitatively determined the functional groups and by FTIR spectroscopy. The complexation behavior of the chemically modified and unmodified HAs with UO22+ions was investigated by time-resolved laser-induced fluorescence spectroscopy. The experimental data were evaluated with the metal ion charge neutralization model. We determined comparable complexation constants for all HAs. Two modified HAs (type M1 and Aldrich) had significantly lower loading capacities for UO22+ions (10.5 ± 0.9% and 9.7 ± 1.6%, respectively) than the corresponding unmodified HAs 18.0 ± 2.0% and 17.5 ± 1.6%, respectively). This indicates that the blocking of the phenolic OH groups changes the complexation behavior of HAs.
Solution coordination chemistry of uranium in the binary UO22+-SO42-and the ternary UO22+-SO42--OH-system
Authors: Moll H. , Reich T. , Hennig C. , Roßberg A. , Szabó Z. , Grenthe I.
Published: August 2006

The structure and reaction dynamics in the systems UO22+-SO42-and UO22+-SO42--OH-were investigated using EXAFS and17O-NMR spectroscopy. Uranium LIIIedge EXAFS indicated a bidentate coordination mode of sulfate to uranyl. In solution, this is characterized by an U-S distance of 3.11 Å. Approximately 5 oxygen atoms were observed in the equatorial plane at 2.39-2.43 Å. The kinetics in the binary uranyl sulfate system can be described by four dominant exchange reactions: (1) UO22++ SO42-⇔ UO2SO4(k1), (2) U*O22++ UO2SO4⇔ U*O2SO4+ UO22+(k2), (3) UO22++ UO2(SO4)22-⇔ 2 UO2SO4(k3), and (4) UO2SO4+ SO42-⇔ UO2(SO4)22-(k4). These reactions have rate constants indicating that the exchange is not of the simple Eigen-Wilkins type.

Ternary uranyl sulfate hydroxide species were characterized by their17O chemical shift and by potentiometry. There are no separate signals for the possible isomers of the ternary species indicating that they are in fast exchange with each other.
The hydrolysis of uranium(VI) in sulfate media
Authors: Comarmond M.J. , Brown P.L.
Published: August 2006

The hydrolysis of uranium(VI) has been investigated in 0.10 and 1.0 mol dm
-3
Na2SO4 using the potentiometric titration technique. Analysis of the data indicates the presence of the following uranyl hydrolysis species: (UO2)2(OH)2
2+, (UO2)3(OH)4
2+, (UO2)4(OH)7
+ and (UO2)5(OH)8
2+ in both media, and additionally, UO2OH+ and (UO2)3(OH)5
+ in the lower ionic strength only. The data were used to calculate stability constants for ternary uranyl hydroxo-sulfate complexes. These constants were found to be in excellent agreement with those found in an earlier study at a higher Na2SO4 concentration (1.5 mol dm-3).
Thermodynamic modeling of metal-ligand interactions in high ionic strength NaCl solutions: the Co2+-oxalate system
Authors: Borkowski M. , Choppin Gregory R. , Moore Robert C.
Published: August 2006

First and second apparent stability constants for cobalt(II) with oxalate ion have been determined using solvent extraction. Data were collected in 0.3 m to 5.0 m NaCl aqueous solutions. The logarithms of first stability constant ranged from 3.30 ± 0.03 to 3.57 ± 0.03 and second stability constant ranged from 5.49 ± 0.05 to 6.02 ± 0.06. The data were modeled using the Pitzer equations. For the 1:1 complex, values of the μ0/RT = -20.3 and the single neutral-ion interaction parameter λ0CoOx-Cl-= -0.161 were determined. For the 1:2 complex, a value for the μ0/RT = -12.4 was calculated from literature data and the Pitzer parameters β0Co(Ox)22--Na+= -0.628; β1Co(Ox)22--Na+= 1.74 and cΦ= 0.251 were determined. Standard chemical potential values are based on a model for oxalate deprotonation reported in an earlier study. Stability constants determined in this work are compared to available values from the literature.
Application of LIBD to the determination of the solubility product of thorium(IV)-colloids
Authors: Bundschuh T. , Knopp R. , Müller R. , Kim J. I. , Neck Volker , Fanghänel Thomas
Published: August 2006

A new experimental method is presented for the determination of solubility data, which is based on the laser-induced breakdown detection (LIBD). The method is capable of monitoring the initial colloid generation when the metal ion concentration reaches or just exceeds the solubility at given pH. The application is made to determine the solubility of Th(IV) in acidic solutions at I = 0.5 M (NaCl) and 25 °C. The initial colloid formation is determined as a function the H+concentration in a series of 2.8 × 10-2- 8.9 × 10-5M thorium solutions. The conditional solubility product (log K´sp= -49.54 ± 0.22) obtained in this study corresponds to an equilibrium between solution and colloidal thorium dioxide particles. The solubility product at I = 0 (log K°sp= -52.8 ± 0.3) is calculated with the SIT coefficients of the NEA-TDB. It corresponds to the known value for crystalline ThO2(cr), in particular if the small particle size of about 20 nm is taken into account. The present results indicate that the high thorium solubilities measured in the previous studies for amorphous Th(IV) hydroxide or hydrous oxide are primarily caused by the inclusion of polynuclear species or Th(IV) colloids of very small size.
The migration behavior of Np(V) in sandy soil and granite media in the presence of humic substances
Authors: Sakamoto Y. , Nagao S. , Ogawa H. , Rao R.R.
Published: August 2006

Migration behavior of Np(V) in sandy soil and granite media was studied in the presence of humic substances using a column method. Two kinds of naturally occurring fulvics were isolated from groundwater at the Chalk River Laboratories of AECL (hereafter, CRL-fulvics) and at the Underground Research Laboratory of AECL (hereafter, URL-fulvics). The commercial humics from Aldrich Co. (hereafter, Aldrich-humics) was also used to compare the influence of humics from different origin on the migration behavior of Np(V). The dominant molecular size of these humic substances was under 5,000 daltons for the fulvics, and in the range from 30,000 to 100,000 daltons for Aldrich-humics. An enhanced elution of Np(V) from the sandy soil column under coexistence of CRL-fulvics at 20 mg/L was observed in comparison with the studies in the absence of humic substances. On the other hand, Np(V) under coexistence of Aldrich-humics was retarded. The difference in the effects of the humic substances on the migration behavior of Np(V) may be caused by the difference in the molecular size distribution of the humic substances. That is, the CRL-fulvics, being smaller in size, has lower sorption ability on the sandy soil than the Aldrich-humics, and thereby Np-fulvics complexes may be able to easily migrate through the sandy soil column. In the case of granite column experiments, again an enhanced elution of Np(V) under the coexistence of URL-fulvics was found and this observation was similar to that found with the CRL-fulvics. From these observations, it is likely that the migration behavior of Np(V) is influenced by the presence of humic substances.
Experimental study and modeling of uranium (VI) transport through ferrous olivine rock columns
Authors: Rovira M. , El Aamrani F.Z. , Duro L. , Casas Ignasi , de Pablo Joan , Bruno J. , Domènech C. , Ayora C.
Published: August 2006

The Lovasjärvi intrusion (SE-Finland) contents a high percentage of ferrous olivine (> 65%). This material has been suggested as a redox-active backfill-additive in deep nuclear waste repositories, due to the large Fe(II) proportion in its mineral composition. In order to understand the processes involved in the redox buffering capacity of this material the transport of uranium (VI) through olivine columns was studied. The results showed considerable retardation factor for the U(VI), particularly in carbonate-free media. The experimental data were simulated by means of reactive transport modeling. The best agreement between the experimental and calculated data was obtained considering that the interaction of U(VI) with the olivine surface occurred at two different types of sorption sites. One type accounts for the sorption capacity of the olivine mineral, and a second type accounts for the sorption on amorphous Fe(OH)3(s) formed at expenses of the oxidative dissolution of olivine.
Sorption of Am(III) and Eu(III) onto γ-alumina: experiment and modelling
Authors: Rabung Thomas , Stumpf Thorsten , Geckeis Horst , Klenze R. , Kim J. I.
Published: August 2006

The present paper describes the surface complexation behaviour of trivalent metal ions, Am(III) and Eu(III), on well characterised γ-alumina. Experiments are conducted at different pH (4-8) and ionic strength (0.001 - 0.1 M NaClO4) either in the presence or absence of CO2. By varying the metal ion concentration from 10-9to 10-4mol/L, the sorption isotherm is established under each given experimental condition. Different surface complexation models are applied to the experimental results to interpret and appraise the surface sorption processes under different experimental conditions. A comparison of the present results is made with the Eu(III) sorption onto the hematite mineral surface investigated previously. It has been shown that sorption properties of hematite and γ-alumina seem to be quite similar. For both systems, a good agreement is found between experimental data and modelling, once using the two site surface complexation model and the same complexation constants for the respective monodentate surface complex. The Eu(III) sorption reaction is additionally studied in-situ by time resolved laser fluorescence spectroscopy (TRLFS). Formation of inner-sphere complexes can be deduced from the emission spectra. The continuous increase of the fluorescence life time with increasing pH starting from pH = 5.0 indicates that surface complexation is accompanied by a decreasing number of hydration water in the first coordination sphere.
Alteration products of uraninite from the Colorado Plateau
Authors: Zhao D. , Ewing Rodney C.
Published: August 2006

Uraninite and associated alteration products from the Colorado Plateau were studied by optical microscopy, electron microprobe analysis (EMPA), scanning electron microscopy (SEM) and backscattered electron (BSE) imaging in order to determine the behavior and fate of trace elements, such as Pb, Ca, Si, Th, Zr, and REE, during corrosion under oxidizing conditions. The long-term alteration products and processes of uraninite may provide insight into the corrosion of the UO2in spent nuclear fuel. Uraninite, schoepite, calciouranoite, uranophane, fourmarierite, a Fe-rich uranyl phase, and coffinite were identified. The primary uraninites and alteration phases generally have low trace element contents, except for coffinite from Caribou Mine, Colorado that has Y2O3as high as 0.88 wt%. The highest Zr, Ti, Th and REE values of the uraninite are ThO20.17, Y2O30.28, La2O30.03, Ce2O30.10, Pr2O30.02, Nd2O30.14, Sm2O30.12, Eu2O30.04, Gd2O30.08, ZrO20.93, and TiO20.54 wt%, which are in general lower than the corresponding components in secondary uranyl phases (the highest values are ThO20.21, Y2O30.88, La2O30.05, Ce2O30.15, Pr2O30.05, Nd2O30.18, Sm2O30.14, Eu2O30.11, Gd2O30.08, ZrO22.11, and TiO22.74 wt%), suggesting that trace elements preferentially enter the structures of these secondary uranyl phases (Table 2). A compositional profile of a concentric structure in schoepite shows that, with increasing alteration, UO2, PbO and ZrO2decrease, and SiO2, TiO2, CaO and P2O5increase. Alteration causes loss of U, Pb and Zr and incorporation of Si, Ti, Ca and P into uranyl phases. The Ca-rich calciouranoite from Grants, New Mexico, indicates an interaction between the limestone host rock and uranium minerals. Texturally, concentric structures and micro-fractures are common. Concentric structures are usually composed of both uraninite and uranyl phases, while micro-fractures are common in the secondary phases.
Fracture-filling minerals as uranium sinks and sources, a natural analogue study at Palmottu, Finland
Authors: Cui Daqing , Eriksen T.
Published: August 2006

The nucleation of a mineral crystal and its growth in groundwater carrying fractures 300 m above the Palmottu uranium deposit provide an impressive example of geochemical selectivity of uranium. Fracture-filling material was collected from a 3 mm thick fracture at depth 74.8 - 75 m (drillcore R348). SEM and EDS analyses on a thin section of the original fracture-filling show that the fracture filling is heterogeneous, composing mineral crystal particles and very porous clay-rich aggregates. The results of INAA on millimetre-sized single mineral crystals and aggregates selected from grinded fracture-filling show that porous aggregates (composed of clays and micrometer sized mineral particles) contain up to 1000 ppm U, which is higher than the average of the whole fracture-filling (400 ppm) and host rock related millimetre sized mineral particles (18 - 100 ppm). 233U/238U isotope exchange proves that a large fraction of the uranium in the fracture-filling is not easily exchanged with uranium in the solution. The amount of 238U released in the isotope exchange experiment is too high to be explained by reversible U(VI) sorption. Oxidation state analyses show that 30% of the uranium exists as U(IV). Laboratory batch experiment at anoxic conditions proved that pyrite can immobilise U(VI).
Actinide partitioning to an acidic, sandy lake sediment
Authors: Loyland S.M. , LaMont S.P. , Herbison S.E. , Clark Sue B.
Published: August 2006

Knowledge of the partitioning of actinides to sediments in natural systems is essential for modeling their environmental fate. Using two different sequential extraction methods, we have studied the partitioning of U and Pu to an acidic, sandy lake sediment that was contaminated due to nuclear production activities. We find that both methods yield similar partitioning information, and that much of the U is associated with insoluble phases, whereas the majority of the Pu is extracted with oxidizable phases, defined to be predominantly organic matter. Our study suggests that U in this ecosystem is of natural origin. Although Pu and Fe in this system are known to cycle from the sediments to the water column during periods of anoxia, only a low percentage of Pu is extracted from the phases that are reducible, which are operationally defined as amorphous Fe oxides. Although this sediment is low in organic matter, our results suggest that natural organics dominate the partitioning of Pu in this system.
An electrostatic approach for the prediction of actinide complexation constants with inorganic ligands-application to carbonate complexes
Authors: Neck Volker , Kim J. I.
Published: August 2006

A new semi-empirical approach is presented for the prediction of actinide complexation constants with inorganic ligands and applied to mononuclear carbonate complexes. The approach is based on an energy term describing the inter-ligand electrostatic repulsion. For a given metal ion M and ligand L, the formation constants log β°nof the complexes MLnare related by:

log β°n= n log β°1-repEL(MLn) / RT ln 10

The electrostatic ligand repulsion termrepELis derived from the charge and inter-distance of ligands involved in a given complex and their angular distribution. Semi-empirical parameters are required to describe the effective electrostatic shielding between complexing ligand ions with the metal ion and hydration water molecules between them. These shielding coefficients are specific for the ligands, but independent of the actinide ion and its oxidation state. The shielding coefficients for carbonate ligands are determined from the known formation constants of Am(III) and Cm(III) carbonate complexes, and then used to calculate carbonate complexation constants for other actinides of different oxidation states. Excellent agreement is found between the calculated and experimental values for Np(V), U(VI), Pu(VI), and even for the transition metals Fe(II) and Cu(II). Based on known constants log β°4and log β°5for U(IV) and Pu(IV), the unknown constants log β°1, log β°2and log β°3are estimated.
Determination and uncertainties of radioelement solubility limits to be used by SKB in the SR 97’ performance assessment exercise
Authors: Bruno J. , Cera E. , Grivé M. , de Pablo Joan , Sellin P. , Duro L.
Published: August 2006

The Swedish Fuel and Waste Management Co, SKB, is at present preparing a Performance Assessment (PA) exercise of its HLNW repository concept. The determination of solubility limits of the main radioelements contained in the spent nuclear fuel is a necessary work to understand their potential migration in both the near and far fields.

The calculated solubilities are compared to experimental data from relevant spent nuclear fuel dissolution tests and field observations from natural systems, particularly Natural Analogue study sites. This work discusses the main uncertainties associated to the calculated solubilities, particularly those related to the variability of groundwater composition, redox conditions and temperature of the system.

The results of the sensivity analysis indicate that although the solubility of some radioelements, such as Th, is not dramatically affected by the uncertainty in the determination of the physico-chemical parameters mentioned above, most of the elements are strongly influenced by this variability, specially Am, U, Np, Pu and Tc.
Distribution coefficients of UO2(NO3)2· 2TBP in supercritical fluid CO2as determined by on-line time resolved laser induced fluorescence
Authors: Addleman R.S. , Wai C.M.
Published: August 2006

Time resolved laser induced fluorescence has been used for on-line analysis of uranium extraction from acidic solutions with tributyl phosphate modified supercritical carbon dioxide. Thein-situmeasurement allows direct characterization of the supercritical fluid extraction. The extractions were found to be first order with respect to uranium and the distribution coefficient was observed to increase with temperature and tributyl phosphate concentration.
Supercritical fluid extraction of plutonium and americium from soil using thenoyltrifluoroacetone and tributylphosphate complexation
Authors: Mincher Bruce J. , Fox Robert V. , Holmes R. G. G. , Robbins R. A. , Boardman C.
Published: August 2006

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 with239Pu and241Am 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.
Thorium isotope fractionation in the dissolution of inorganic samples by a microwave method
Authors: Lozano J. C. , Tomé F. V. , Rodríguez P. B.
Published: August 2006

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.
Characteristics of two fission modes
Authors: Nagame Y. , Zhao Y.L. , Nishinaka I. , Goto S. , Kaji D. , Tanikawa M. , Tsukada K. , Asai M. , Haba H. , Sakama M.
Published: August 2006

Characteristics of nuclear deformation properties at scission of two fission modes, symmetric and asymmetric, are reviewed. Existence of two kinds of scission configurations associated with the symmetric and asymmetric fission modes is pointed out: elongated and compact configurations. Each symmetric and asymmetric scission property is discussed in terms of shape elongation evaluated from fragment total kinetic energy (TKE). Fragment deformation at scission is also discussed based on neutron multiplicity data. From the systematic study of the scission properties in a wide range of actinide fission, the bimodal fission observed in spontaneous fission (SF) of the heavy actinides is interpreted as the result of the presence of the two fission paths of the ordinary asymmetric mode and a strongly shell-influenced symmetric one. The correlation between the fragment shell structures and the asymmetric mass-yield curves is described.
Quantum chemical predictions of properties and experimental behaviour of elements 106, 107, and 108
Authors: Pershina Valeria , Bastug T. , Kratz Jens Volker
Published: August 2006

Fully relativistic Density-Functional calculations have been performed for group 7 MO3Cl (M=Tc, Re, and element 107, Bh), for group 8 tetroxides MO4(M=Ru, Os, and element 108, Hs), and for various aqueous complexes of group 6 elements Mo, W, and element 106, Sg. The electronic structure analysis has shown the transactinide compounds to be very similar to those of the lighter homologs in the respective chemical groups with the covalence increasing with increasing atomic number. Results have shown BhO3Cl to have a trend in volatility in line with that of the lighter homologs in the group. Hydrolysis of element 106 with the formation of anionic oxo-complexes has, however, a reversed trend, so that hydrolysis decreases in the order Mo>Sg>W.
Startup of transactinide chemistry in JAERI
Authors: Haba H. , Tsukada K. , Asai M. , Nishinaka I. , Sakama M. , Goto S. , Hirata M. , Ichikawa S. , Nagame Y. , Kaneko T.
Published: August 2006

The transactinide nuclides261Rf and262Db have been successfully produced in the248Cm(18O,5n) reaction at 99 MeV and in the248Cm(19F,5n) reaction at 100, 103, and 106 MeV, respectively, at the JAERI tandem accelerator. The on-line ion exchange experiments with an automated fast and repetitive liquid chromatography separation system were performed in the HNO3/HF system using Rf homologues89mZr and167,165Hf produced in the89Y(p,n) and152Gd(18O,xn) reactions, respectively. The radiotracers88Zr,175Hf, and234Th were also prepared and the distribution coefficients on ion exchange resins were measured systematically in 1-11 M HCl and 1-14 M HNO3with the batch method. It was found that anion exchange experiments of Rf in 8 M HNO3and 9 M HCl provided information useful to extract the ionic radius of Rf and to verify the influence of relativistic effects.
First attempt to chemically identify element 112
Authors: Yakushev Alexander B. , Buklanov G. V. , Chelnokov M. L. , Chepigin V. I. , Dmitriev S. N. , Gorshkov V. A. , Hübener S. , Lebedev V. Ya. , Malyshev O.N. , Oganessian Yu. Ts.
Published: August 2006

The first attempt to chemically identify one of the recently discovered long-lived isotopes of superheavy elements, namely 283112 (3 min, SF), made at FLNR, Dubna is reported. The nuclide was produced by fusion of accelerated 48Ca with a target of natural U, which contained some Nd to simultaneously produce also short-lived Hg nuclides. According to test experiments with Hg, the expected lighter homologue of element 112, both elements can be isolated from the products of the bombardment in metallic state, and transported from the target in flowing He gas to a detection system, where spontaneous fission and alpha decays 49-s 185Hg) were registered using PIPS detectors. The surface of the detectors was covered with a thin layer of Au or Pd which ensured the detection of Hg with high efficiency due to its chemisorption on these surfaces. While about three SF events could be expected, not a single one was detected at an upper limit for the production cross section of about one picobarn. This may point to a "Rn-like" rather than "Hg-like" behavior of element 112. A new experiment is planned, in which both a "Rn-like" and a "Hg-like" species could be detected.
Radionuclide speciation in the environment: a review
Authors: Moulin Valérie , Moulin Christophe
Published: August 2006

Speciation determination is of prime importance to explain and evaluate the mobility, the toxicity and the risk resulting from the presence of trace elements in natural systems, in particular in the case of radionuclides, in the framework of environment and waste management purposes. The present paper will then focus more specifically on the physico-chemical speciation of radionuclides, and more particularly of actinides, in the environment, with emphasis on the behavior in solution: from a chemical point of view (with important ligands including colloidal phases) using experimental data and speciation calculations, as well as from a more technical point of view (with analytical methods forin situspeciation determination and thermodynamic data determination). A review of recent papers (mainly from CEA) is presented.
Sorption studies of Cs+, Ba2+, and Co2+ ions on bentonite using radiotracer, ToF-SIMS, and XRD techniques
Authors: Shahwan T. , Erten H.N.
Published: August 2006

The sorption behaviour of Cs+, Ba2+, and Co2+ ions on bentonite were investigated using the radiotracer method, Time of Flight-Secondary Ion Mass Spectroscopy (ToF-SIMS), and X-Ray Diffraction (XRD). The sorption of Cs+ and Ba2+ were exothermic while sorption of Co2+ was endothermic. The sorption data were well described by Freundlich and Dubinin-Radushkevich isotherms. According to ToF-SIMS results Na+ and Mg2+ were the primary exchanging ions in bentonite. The XRD spectra showed that no structural changes were associated with the sorption of Cs+ and Co2+, and BaCO3 precipitate was formed upon the sorption of Ba2+ on bentonite.
Pollutant concentrations in a sediment core dated by Th-isotopic ratios and the 210Pb dating method
Authors: San Miguel E.G. , Bolívar J.P. , García-Tenorio R. , Martín J.E.
Published: August 2006

In this research we have dated a sediment core in an estuarine system (southwest of Spain) strongly contaminated by anthropogenic activities, making use of the enhanced levels of some natural radionuclides from uranium series found in the upper layers of the core due to these activities and applying the 210Pb dating method in the remaining ones. This chronology has allowed to explain the concentration profile along the sediment core of some heavy metal (Fe, Cu, Zn and U), which have been introduced in this estuary by mining and industrial activities.
Production of positron emitters of metallic elements to study plant uptake and distribution
Authors: Watanabe S. , Ishioka N.S. , Osa A. , Koizumi M. , Sekine Tsutomu , Kiyomiya S. , Nakanishi H. , Mori S.
Published: August 2006

The metallic positron emitters 52Mn, 52Fe and 62Zn, the elements of which are essential nutrients for plants as well as for animals, have been produced for a new tracer method in plant physiology. The tracer method utilizes the detection of annihilation γ-rays, like PET in nuclear medicine, to obtain two-dimensional images on a plant as well as to obtain radioactivity counts at specified points in a plant; this method allows us to observe the tracer movement in a living plant without touching the test plant. The previously reported methods of radiochemical separation of these metallic positron emitters from targets were partly modified from the view of their use in plant physiology. Radionuclidic impurities remaining in the final solutions were examined by γ-ray spectrometry, and their influences on the above-mentioned measurements are discussed. From the experiments on a barley plant, the speeds of 52Mn2+ ion and 52Fe3+-mugineic-acid complex have been obtained for the first time to be 0.2 cm/min and 1.0 cm/min, respectively.
Formulation and preliminary clinical application of the 99mTc(V)-dimercaptosuccinic acid "instant" kit
Authors: Ayranov Marin , Jordanova A. , Mladenov B. , Stantchev V. , Kouykin V.
Published: August 2006

99mTc labelling of DMSA under moderate reduction conditions (alkaline pH and low concentration of Sn(II) leads to formation of various DMSA complexes. One of them 99mTc(V)-DMSA is proved to be suitable for tumour imaging in nuclear medicine diagnostics. The aims of our study were to define the optimum terms for high yield of 99mTc(V)-DMSA complex and kit formulation, which can be conveniently applied for diagnosis in nuclear medicine laboratories. The 99mTc labelled DMSA complexes were analysed by means of ascending thin layer chromatography (TCL) in three mobile phases - methyl ethyl ketone, n-butanol/acetic acid/water 3/2/3 and 0.154 M NaCl. Appropriate formulae were chosen for kit preparation and applied for preliminary clinical investigations.
Luminescence study on solvation of americium(III), curium(III) and several lanthanide(III) ions in nonaqueous and binary mixed solvents
Authors: Kimura T. , Nagaishi R. , Kato Y. , Yoshida Z.
Published: August 2006

The luminescence lifetimes of An(III) and Ln(III) ions [An=Am and Cm; Ln=Nd, Sm, Eu, Tb and Dy] were measured in dimethyl sulfoxide(DMSO), N,N-dimethylformamide(DMF), methanol(MeOH), water and their perdeuterated solvents. Nonradiative decay rates of the ions were in the order of H2O > MeOH > DMF > DMSO, indicating that O-H vibration is more effective quencher than C-H, C=O, and S=O vibrations in the solvent molecules. Maximal lifetime ratios τD/τHwere observed for Eu(III) in H2O, for Sm(III) in MeOH and DMF, and for Sm(III) and Dy(III) in DMSO. The solvent composition in the first coordination sphere of Cm(III) and Ln(III) in binary mixed solvents was also studied by measuring the luminescence lifetime. Cm(III) and Ln(III) were preferentially solvated by DMSO in DMSO-H2O, by DMF in DMF-H2O, and by H2O in MeOH-H2O over the whole range of the solvent composition. The order of the preferential solvation, i.e., DMSO > DMF > H2O > MeOH, correlates with the relative basicity of these solvents. The Gibbs free energy of transfer of ions from water to nonaqueous solvents was further estimated from the degree of the preferential solvation.
Determination of mass transfer coefficients of 99Tc(VII) in forward and backward transport in PUREX-relevant systems by using analytical ultracentrifugation
Authors: Ludwig R. , Nguyen T.K.D. , Nabeshima M.
Published: August 2006

The lack of published data on the extraction kinetics of Tc(VII) in the system U(VI)/HNO3//TBP/dodecane prompted us to investigate its transport behaviour in detail. The aim was to improve the U(VI)/Tc(VII) separation in the PUREX process. We choose the method of analytical ultracentrifugation to determine the concentration gradient profile, the initial flux density and the integral mass transport for both sides of the unstirred liquid-liquid interface as well as the overall mass transfer coefficients as a function of Tc(VII)-, U(VI)-concentrations and temperature from time-dependent changes of the refractive index gradients. The results were supplemented by comparing the experimental with calculated concentration profiles, obtained by modeling a diffusion-limited extraction process. In some of the investigated systems, the transport at the interface is reaction-limited after phase contact. The determined values of J
max, I, and α are discussed in terms of the extraction conditions.
Dosimetry related to SPECT and PET applications
Authors: Herzog H.
Published: August 2006

Nuclear medicine methods permit the in vivo measurement of physiological and metabolic functions. For this purpose metabolically active molecules are labelled with radionuclides. After the injection, these radiopharmaceuticals can be detected from outside the body with appropriate detectors such as conventional gamma cameras, single photon emission computerized tomographs (SPECT), or positron emission tomographs (PET). As with any application of ionizing radiation the benefits of nuclear medicine (the diagnosis and treatment of disease) must be balanced against the risks of the procedures. Risks in nuclear medicine are evaluated through dosimetry, the calculation of the radiation dose estimates, in which the energy deposited by the radiation in human tissues is quantitated. The first step of dosimetry is the determination of the biodistribution, i.e. the spatial and temporal distribution of the radiopharmaceutical within the body. When a new radiopharmaceutical is introduced such data are first derived from ex vivo experiments in animals. Further evaluations of the biokinetics and dosimetry are carried out via quantitative measurements in humans using the nuclear medicine imaging equipment, applying whole-body planar and tomographic methods. Based on the knowledge of the biodistribution and using the framework introduced by the MIRD committee as well as by the ICRP, the radiation dose to single organs and to the total body can be calculated. The purpose of this paper is to review methods for measuring radiopharmaceutical biodistributions in humans and for calculating the appropriate radiation dose quantities.
Overview of hadron therapy: rationales, present status and future prospects
Authors: Jones D.T.L.
Published: August 2006

The rationales for hadron therapy are based on the physical selectivity and biological effects of the respective beams. Fastneutron therapy began as long ago as 1938 and subsequently proton, alpha particle, heavy ion, pion and neutron capture therapy have beenused. To date it is estimated that in excess of 50000 peoplehave undergone some form of hadron therapy. In the future it isexpected that fast neutron therapy will be used for selected tumourtypes for which neutrons are known to show improved cure rates. Thefuture trends in charged particle therapy will be driven by increasingcommercialization. The future of neutron capture therapy will dependon current clinical trials with epithermal neutron beams and thedevelopment of new tumour-seeking drugs.
What accuracy is required and can be achieved in radiation therapy (review of radiobiological and clinical data)
Authors: Wambersie A.
Published: August 2006

An attempt is made to formulate the requirements for the accuracy in the delivery of absorbed dose to a patient during radiation therapy. These requirements are mainly based on the relative steepness and separation of the dose-effect curves for local tumour control and normal tissue damage. The curves for normal tissue complications in general may be steeper than those for local tumour control. From these data, a standard requirement of 3.5% is proposed for the combined uncertainty of type A (random) and type B (systematic), given as one relative standard deviation in the absorbed dose delivery. However, it is recognized that, in many cases, larger uncertainties are acceptable palliative treatments). This value of 3.5% applies to the absorbed dose at the specification point for curative treatments. As far as the dose accuracy requirements at other points in the planning target volume are concerned, a value of 5% (one standard deviation) seems more appropriate. This required accuracy in the delivery of the absorbed dose cannot always be completely achieved in photon therapy even for simple treatment conditions. All the clinical data which were reviewed, including some results from the ldquo;Patterns of Care Study”, indicate a close correlation between the outcomes of therapy (control rates, complications) and dose level, inaccuracy or errors in dosimetry and patient-machine positioning. This has been reported for external beam therapy as well as for brachytherapy. Only the clinical results will allow us to select the optimal treatment conditions (e.g. selection and definition of the planning target volumes, dose levels and beam arrangement), but they could be interpreted correctly only to the extent that the treatment execution would be correct. This result strongly endorses the Quality Assurance Programmes, in which the clinicians and physicists should be fully involved. Lastly, the outcome of a treatment can only be interpreted meaningfully if the parameters of the irradiation, in particular, the distribution of dose in space and time can be accurately correlated with the type and extent of the disease. It is essential that clear, well defined and unambiguous concepts and parameters be used for reporting purposes to ensure a common language between collaborating centres. This is one of the major tasks that the ICRU undertook several years ago.
Therapeutic radionuclides and nuclear data
Authors: Qaim Syed M.
Published: August 2006

The nuclear data required for the production and endotherapeutic application of radionuclides are outlined. The three types of therapeutic radionuclides, viz. β--emitters, α-emitters and Auger electron emitters, are considered and the role of some β+-emitters in therapy planning is discussed. The status of available data is reviewed.