Showing papers in "Radiochimica Acta in 1986"

Third Phase Formation in the Extraction of Plutonium by Tri-n-Butyl Phosphate

Abstract: Third phase formation in the extraction of plutonium(IV) by tri-n-butyl phosphate (TBP) in n-dodecane (DD) and Shellsol-T (SST) was studied. The effect of ionic strength on the limiting organic concentration (LOC) in Pu(N03)4 /30% TBP/DD system was studied and the LOC was found to increase nearly linearly with aqueous phase ionic strength. Data for the LOC of plutoniurndV) in 15% TBP/SST, 30% TBP/SST and 30% TBP/DD as a function of equilibrium aqueous phase acidity indicate, as expected, a mach higher solubility of the Pu(N03 )< • 2 TBP complex in SST than in DD.

Migration of the Fission Products Strontium, Technetium, Iodine and Cesium in Clay

Abstract: The migration in compacted bentonite i. e., the diffusivity, of the fission products strontium, technetium, iodine and cesium have been studied in laboratory experiments. The clay used in the experiments was a sodium bentonite, Wyoming Bentonite MX-80, compacted to a density of 2000 kg/ m 3 . The aqueous phase was synthetic groundwater representative of Swedish deep granitic groundwaters, and was preequilibrated with the clay. The influence of complex-forming and redox controlling agents was studied by mixing the clay with small amounts of the chemical reagents PbO, KMn04 or powdered iron, or the minerals chalcopyrite/pyrite or cinnabar. The diffusivity of strontium was on the order of 10\" 1 m? /s. For cesium and technetium (as pertechnetate) under oxidizing conditions the diffusivities are on the order of 10\" 1 1 m 1 Is; for technetium under reducing conditions the diffusivity is about one order of magnitude lower. Iodine appears to diffuse with two mechanisms, resulting in two diffusion rates one close to 10\" 1 2 m Is and the other one-tenth slower, 10\" 3 m 1 Is, contributing to the observed overall apparent diffusivity.

Separation of Cesium from Acid ILW-Purex Solutions by Sorption on Inorganic Ion Exchangers

Abstract: The separation of cesium by use of the inorganic ion exchanger ammonium molybdatophosphate from nitric acid solutions of intermediate level waste (ILW) from reprocessing of spent fuel elements according to the PUREX PROCESS has been demonstrated. Other inorganic exchange materials have shown high sorption values only for certain pH ranges: ammonium hexacyano cobaltous ferrate (pH 12, 35 g Cs/kg) potassium hexacyano nickel ferrate (pH 10, 30 g Cs/kg) zirconium phosphate (pH 7, 100 g Cs/kg) titanium phosphate (pH 7, 15 g Cs/kg) antimony pentoxide (pH 2, 30 g Cs/kg) titanium oxide (pH 7, 1 g Cs/kg) Except for high salt loading of 3.6 AT NaN03 , a significant loss of capacities usually occurs; this does not allow the use of these exchangers. However, ammonium molybdatophosphate shows excellent performance with high salt loadings and in a broad pHrange from pH 9 to conc. HN03 with a breakthrough-capacity of 60 g Cs/kg.

Sorption of Trace Elements or Radionuclides in Natural Systems Containing Groundwater and Sediments

Abstract: A general formula for the sorption ratio that is observed experimentally in natural systems is presented taking into account three kinds of processes: sorption at the outer surface of the solid particles, sorption in porous particles and one-directional processes such as precipitation or coprecipitation. These various processes as well as the mechanisms and the kinetics of sorption are discussed. The sorption of radioactive Cs, S r 2 + and Ce 3 + is studied in two selected natural sediment/groundwater systems, one of low and one of high salinity, under various conditions. Cs ions are mainly sorbed in clay minerals that are suspended in the groundwater with relatively high sorption ratios, S r 2 + ions are mainly sorbed on the sediments with relatively low sorption ratios, and Ce 3 + is mainly found in form of colloids or in suspended particles or in coprecipitates. Coprecipitation leads to very high sorption ratios for Ce 3 + . The behaviour of Cs, Sr 2 + and Ce 3 + is typical for all elements with similar properties.

The formation of Pu(IV)-colloid by the alpha-reduction of Pu(V) or Pu(VI) in aqueous solutions

Abstract: The effects of alpha-particle self-irradiation have been investigated in solutions of {sup 239}Pu in the pH range from 1.3 to > 2.2. The initial solutions contained Pu(VI), Pu(V), colloidal Pu(IV) or various mixtures of these. Composition versus time was determined for periods up to 618 days. Colloidal Pu(IV) formed slowly in mixtures with initial average oxidation states greater than about 4.5. Colloidal Pu(IV) reacts slowly to give mixtures of Pu(V) and Pu(VI). The two most important reactions in the system appear to be: the disproportionation of Pu(V) to give Pu(VI) and colloidal Pu(IV), and the alpha-particle induced reduction of Pu(VI) to give Pu(V). Steady-states were reached very slowly and required at least 400 days for most of the mixtures. No evidence was found for equilibrium in the disproportionation reaction. 20 refs., 4 figs., 3 tabs.

Colloid formation and sorption of radionuclides in natural systems

Abstract: Natural systems comprising sediments and groundwater of low and of high salinity are investigated with respect to the formation and the influence of coarsely dispersed particles and finely dispersed particles (colloids). Equations are derived for the sorption equilibria in such systems and it is shown that the efficiencies of mutual separation of coarsely dispersed particles, finely dispersed particles and sediments (efficiencies of filtering) strongly influence the sorption ratios that are observed. In groundwater without sediments the formation of colloids of radioactive Ce/sup 3+/ is demonstrated, whereas Cs/sup +/ and Sr/sup 2+/ do not form colloids under these conditions, as expected. The amount of elements and of colloids given off by the sediments into the groundwaters are measured for the samples of low and of high salinity and the influence of agitation is shown. Sorption ratios of radioactive Cs/sup +/, Sr/sup 2+/, and Ce/sup 3+/ are investigated as function of the ratio of groundwater volume to the mass of the sediment without filtration, after filtration through 0.45 ..mu..m filters and after ultrafiltration. The results are discussed on the basis of the equations derived. It is shown that Cs/sup +/ ions are sorbed mainly on the clay particles and that the larger amount of these clay particles has grain sizes greater than 0.45 ..mu..m under the experimental conditions of smooth shaking. Sr/sup 2+/ ions are mainly sorbed on the sediments with a relatively low sorption ratio. Ce/sup 3+/ ions form colloids (''Eigenkolloide'') that are retained by ultrafiltration.

Migration of the Actinides Thorium, Protactinium, Uranium, Neptunium, Plutonium and Americium in Clay

Abstract: The migration, i. e., the diffusivity, in compacted bentonite of the actinides thorium, protactinium, uranium, neptunium, plutonium and americium have been studied in laboratory experiments. A sodium bentonite, Wyoming bentonite MX-80, compacted to a density of 2 X 10 kg/m, was used in all experiments. The effect of mixing the clay with 1% Fe, (P04), or 0.5% iron powder on the diffusion of uranium and neptunium was examined. The diffusion of uranium and americium after addition of 600 mg/1 of HCO¡ and the diffusion of uranium after addition of 10mg/l of humic acid to the aqueous phase was studied, as well. The aqueous phase was a synthetic groundwater representative of Swedish deep granitic groundwaters, and was preequilibrated with the clay. The apparent diffusivities measured for the pentaand hexavalent actinides

Isotopic Fractionation of Uranium: Extremely High Enrichments of 234U in the Acid-Residues of a Colorado Carnotite

Abstract: Uranium fractions in which the 2 3 4 U / 2 3 , U ratios were as high as 103±7 and 116±11 (Ci/Ci) were obtained in the uraniumpoor residues of a Colorado carnotite and in their chemical and physical separates. Extremely high enrichment of 1 3 4 U relative to , 3 , U occurs when 1 3 U atoms recoil into the uranium-poor phase from the adjacent uranium-rich phase, and the former becomes enriched in the recoil 2 3 4 U atoms when it is removed from the latter by the selective dissolution or other means.

Liquid-liquid Extraction of Pa(V) and U(VI) by Dialkyl Sulphoxides

Abstract: The liquid-liquid extraction of protactinium(V) from HCl solutions by dipentyl and dioctyl sulphoxides (DPSO and DOSO, respectively), tributyl phosphate (TBP) and theii mixtures in diluents over a wide ränge of conditions has been studied. The species extracted appear to be PaOO, • 3 DPSO, PaOCl, • 3 DOSO and PaOClj 2 TBP. The mixtures of extractants exhibit synergism. The extraction of Pa(V) increases roughly linearly with decrease in the dielectric constant of the diluent. In the extraction of uranium(VI) from HCl solutions by a series of sulphoxides (R, SO) from dipentyl to didecyl, the extracted species appear to be of the type UO, O , • 3 R , SO and/or UO, Cl, • HO • 3 R, SO. Dipentyl and dioctyl sulphoxides are shown to be better extractants. The extraction efficiency of the sulphoxides follows the order: dioctyl > dipentyl > diheptyl > dinonyl > dihexyl > didecyl sulphoxide at any aqueous acidity of the ränge studied. A comparative study of the extraction of zirconium(IV), thorium(IV), protactinium(V), and uranium(VI) with dipentyl sulphoxide (DPSO) shows that the metals can be separated from one another under controlled conditions of aqueous phase acidity.

Vacuum-Thermochromatography of Carrier-free Species

Abstract: In thermochromatography volatile speeies are separated by sequential deposition in a tube with a stationary temperature gradient. Each speeies is adsorbed at a characteristic deposition temperature. Most applications performed so far by this technique used carrier gases for the transportation of the volatile speeies through the tube. The minimum time needed to separate two chemical components is strongly influenced by the velocity of the mobile phase, i. e. the carrier gas. Under favourable conditions Separation times of the order of one second can be reached [1]. For the study of very short-lived nuclei, even shorter Separation times would be a prerequisite; such conditions may be achieved by performing thermochromatographic separations at reduced pressure. If the pressure is reduced below a critical value, molecular flow pattern is reached and only collisions of volatile speeies with the surface of the Chromatographie tube occur. This is in contrast to gasthermochromatography, where migration of volatile speeies occurs by collisions with both the surface of the tube and the carrier gas atoms or molecules [2]. In vacuumthermochromatography the drift velocity is a function of the following four parameters [3]:

Extraction of TcO-4 Ions by Use of Crown Ethers from Sulphuric Acid Solutions

Abstract: The extraction of TcO, by dibenzo-18-crown-6 in 1,2-dichloroethane was studied from sulphuric acid medium. The effects of crown cavity size, substitutions, organic solvent on the distribution coefficient were discussed. TcO^ can be separated with high separation factor from irradiated uranium samples.

Measurement of 10b (n,t) 2a reaction cross section in the energy range of 2.5 to 10.6 mev: Diffusion of tritium in boron carbide

Abstract: Cross sections were measured for the reaction \" B (n, t) 2 a using tritium counting. A deuterium gas target was used to obtain quasimonoenergetic neutrons of energies between 2.5 and 10.6 MeV via the reaction ' H (d, n) ' He. Tritium was separated by vacuum extraction and measured in the gas phase using an anticoincidence proportional counter. A special technique involving high-temperature chemical reaction of irradiated \" B with PbO (resulting in the release of tritium) was employed to determine the residual tritium content in the sample. The cross sections lie between 39 and 215 mb (with the maximum at about 5.5 MeV) and have an uncertainty of 13 to 21%. The characteristics of tritium diffusion in B4 C were studied by high temperature release experiments. From the Arrhenius plot the activation energy is deduced to be 196 ± 30 kJmol-' in the temperature ränge of 550 to 680° C.

Extraction Equilibrium and Crystal Structure of Hydronium—Uranium(IV) - Dicyclohexano-18-crown-6 Isomer A Complex

Abstract: The extraction equilibrium of tetravalent uranium from hydrochloric acid solution with dicyclohexano-18-crown-6 isomer A (la) in 1,2-dichloroethane has been studied. The extracted species is found to be 1 : 2 (metal/crown) from slope analysis and direct determination of the extracted complex. The value of the extraction equilibrium constant ( K e x ) at 25°C is 1.12. The extracted complex has the overall composition (Ia)2 · ( H 3 0 + ) 2 · UCl^ The crystal structure of this complex was determined by X-ray diffraction method. Crystals are monoclinic, space group Ρ2 , /c, a = 12.746(1), b = 29.898(4), c = 14.575(3) Α, β= 108.08(10)° and Z = 4. The structure consists of two complex cations ( I a H 3 0 + ) and a complex anion (UCl^ \"). The uranium atom is not directly bonded to the ether oxygen and is surrounded by six Cl~ ions forming an octahedral anion. In the complex cations, each of the two H 3 0 + ions is anchored in the crown ether cavity by three OH . . . O hydrogen bonds (distances approximately 2.65 A). The separation of U(IV) and U(VI) in this extraction system, as well as IR and NMR data of the complex are also discussed.

Separation and Determination of Neptunium, Plutonium, and Americium Using Coprecipitation with Barium Sulfate

Abstract: The coprecipitation of neptunium, plutonium, and americium with barium sulfate was studied under various conditions of kinds of acid, acidity, and amounts of sodium, potassium, and barium. The results gave an optimum condition under which these actinides were quantitatively coprecipitated with barium sulfate. Furthermore, sequential separation of neptunium, plutonium, and americium was accomplished by combining the coprecipitation with barium sulfate and reduction /oxidation of the actinides. barium sulfate, successive separation of uranium, neptunium, plutonium, americium, and curium can be attained by adding proper oxidizing or reducing agents at appropriate stages. A satisfactory result was obtained using KMn04 as an oxidizing agent and NaN02 and NH2 OH · HCl as reducing agents.

Dependence of the Angular Momenta of Fission Fragments on their Nuclear Structure

Abstract: In order to investigate the influence of the nuclear structure of a fission fragment on the scission configuration, angular momenta of 13 1 fragment have been deduced from the radiochemically determined independent isomeric yield ratios of 1 in the fission of 2 3 U, 2 3 U, 1 3 , Pu and 3 , 1 Pu induced by thermal neutrons. An odd-even effect observed in the angular momentum of the fragment indicates a greater extent of deformation in the odd-Z fragments; the angular momentum of the 1 3 I fragment decreases when the neutron number of the complementary fragment approaches the 66 η deformed shell configuration.

Determination of Fractional Cumulative Yields of 91Sr, 92Sr and 134Te in the Thermal Neutron Induced Fission of 233U and 241Pu

Abstract: Fractional cumulative yields (FCY) of " S r , " S r and , 3 4 T e have been determined in the thermal neutron fission of 2 3 3 U and 1 4 1 Pu. Present results together with published data on other fissile nuclides have been analysed in the light of variations of the most probable charge and the extent of charge polarization as a function of the fissionability parameter. The FCY vary linearly as a function of the fissionability parameter. The interpretation is based on the dependence of the charge polarization on the mass-asymmetry.

Separation of Plutonium Oxidation States by Ion Exchange Chromatography

Abstract: A systematic study of the ion exchange behavior of Pu ' Pu* PuO^ and PuO' has been performed using five organic and inorganic cation exchangers. The distribution coefficients of Pu'''\", Pu*\"^ and PuO^\"^ were determined in HCl or HCIO^ solutions by batch experiments, with the acid concentrations ranging over four Orders of magnitude. The plutonium concentrations were measured in both phases by delayed neutron counting of fission products subsequent to irradiations with reactor neutrons. From consecutive column experiments, a Separation scheme was developed based upon a two column procedure. Its application to the Separation of Pu''' '-Pu'\"'\"-Pu02 dissolved in synthetic groundwater at a plutonium concentration level of 1 0 \" \" Af yielded results which were consistent with the initial composition as well as with results obtained by LaF3-coprecipitation.

Identification of Oxidation States of Ultra-trace Elements by Radiation Detection

Abstract: The determination of the oxidation state of ultra-trace elements in the environment, especially in the case of actinides, is of importance in many ways. Speciation techniques using radiation may comprise methods based on the detection of the nuclear and atomic radiations emitted in radioactive decay or methods using external sources of excitation. In the former instance, information can be obtained from the energy and intensity of radiation, but at present the partition method is still the most commonly used, although its reliability is questionable. Excitation with intense laser beams, as is currently being used for trace element analysis in photoacoustic and thermal lensing spectroscopic techniques, could conceivably be applied under suitable conditions to ultratrace elements with a sensitivity approaching that of the radiochemical methods.

Extraction of Zinc(ll) and Europium(lli) by Thenoyltrifluoroacetone and Triphenylphosphine or Triphenylarsine Oxides in Chloroform

Abstract: Zn(II) and Eu (III) were extracted by thenoyltrifluoroacetone (ΗΤΤΑ) and triphenylphosphine oxide (Ph3 PO) or triphenylarsine oxide (Ph3 AsO), (L), in chloroform from Perchlorate aqueous media. The chelate extraction constant (Κχ,ο), the mixed extraction constant (ATX> y ) , the synergic factor (S. F.) and the adduct formation constant (βΧι y ) of the respective extracted species were elucidated. The stoichiometry of the adducts extracted were established to be Zn(TTA)2 L and Eu(TTA)3 L,. The synergic values Kx¡ y , β χ y and S. F. as related to these oxides confirmed the superiority of Ph3 AsO over Ph,PO as adduct forming ligand irrespective of the metal extracted. This was explained on the basis of the electron donating properties of these oxides.

The Effect of Complexing Agent on the Extraction of Lanthanides by Di(2-Ethyl Hexyl) Phosphoric Acid.

Abstract: Liquid-liquid extraction of neodymium, terbium and thulium has been studied using di(2-ethyl hexyl) phosphoric acid (HDEHP) in cyclohexane as the extractant. The effect of glycine on the extraction has been investigated. The role of acidity on the distribution ratios of the lanthanide ions is explained by means of the equilibria involved in the system. An improvement in separation factor is observed and the best conditions of separation are proposed.

Study on the Effect of the Number of Carbon Atoms in Alkyl Group on the Reactivity of Carboxyl or Hydroxyl Group in a Liquid Compound Using Hydrogen Isotope Exchange Reaction

Abstract: Isotope exchange reaction has been investigated using PVA labeled with tritium and liquid, unlabeled compounds (alcohols or carboxylic acids). Activity due to tritium has been measured that has been transferred from the PVA to a liquid compound. The time dependence of the activity has been analysed using McKay plot. The following ((a) ~ (d)) have been found, (a) For alcohols, the greater the number of carbon atoms in the alkyl group, the less is the rate constant at 30° C ~ 70° C. (b) For carb-. oxylic acids, the same relation can be seen at 70° C. (c) For both alcohols and carboxylic acids, a relation can be seen such that the greater the number of carbon atoms in the alkyl group, the less is the activation energy, (d) For these materials, the temperature dependence of acidity (based on kinetic logic) is much larger than that of pK.

Liquid-Liquid Extraction of Trivalent Actinides and Lanthanides with N-Benzoyl-N-Phenyl Hydroxylamine

Abstract: Extraction of the trivalent actinides Am, Cm, Bk and Cf and the trivalent lanthanides Pm, Eu, Tb, Tm and Lu has been studied with N-benzoyl-N-phenyl hydroxylamine (HBPHA) in chloroform in the pH range 3.5-4.5. At pH 4.5 slopes of the logD vs. log [HBPHA] plots progressively decrease from 4 to 3 with increasing Ζ of the ions. Similar plots at pH 4.0 gave a uniform slope of 4 in all cases indicating the extraction of M(BPHA)3 HBPHA (M = An, Ln). In the pH ranges where this species is extracted log D vs. pH plots gave straight lines with slopes increasing from 2.0 to 2.7 with Ζ instead of the expected value of 3.0. Reasons for these abnormalities are discussed. Ο.ΙΛί NaC104 (pH between 3.5 and 4.5). Eu carrier ( ~ 50 Mg/ml) was added to the aqueous phase in all experiments to avoid radio-colloid formation. Effect of HBPHA concentration 0.5 ml of the aqueous phase whose pH was maintained constant at the required value was equilibrated with an equal volume of chloroform solution of varying HBPHA concentrations, ranging from 0.1 to 0.2M. The equilibrations were carried out in a thermostated bath at 30 ± 0.1 °C for one hr though the equilibrium was found to be reached in 30 minutes.