[en] An exhaustive bibliographic review on hydrolysis of americium gives the stability constants, at zero ionic strength. No evidence of Am(OH)₄^- formation was found by solubility studies up to pH < 13. The solubility of solid Am₂ (CO₃)₃ characterised by its X-ray diffraction pattern is studied at a high ionic strength. All the published results on Am in carbonate media are reinterpreted using these stability constants (Am-OH-CO₃ complexes are not needed). No evidence of Am(CO₃)₄^5- formation was found by spectrophotometry up to 3M. Literature results are used to determine the formal redox potentials at pH = 9.4 and to calculate the formation constants, at zero ionic strength. The formation of complexes between americium and humic materials (purified fulvic and humic acids) has been studied by a spectrophotometric technique. The results are interpreted by the formation of a 1:1 complexe. Solubility of the solid PuO₂(CO₃) is measured in bicarbonate media at high ionic strength, to obtain the solubility product and formation constants of the PuO₂(CO₃)_i^2-2i complexes

[en] By using spectrophotometric and potentiometric methods it is shown that, in media of high ionic strength (NaClO₄ 3M) and total concentrations of hexavalent actinoids higher than 10^-3M, trimers are formed. The equilibrium constants for the reactions 3MO₂(CO₃)₃^4- reversible (MO₂)₃(CO₃)₆^6- + 3 CO₃^2- are log K (U) = -11,3; log K (Np) = -10,1 and log K (Pu) = -7,4. It is demonstrated that one of the cations of the trimer can be exchanged with another actinoid cation: the equilibrium constants for the reactions 2UO₂ (CO₃)₃^4- + MO₂ (CO₃^4- reversible (UO₂)₂ MO₂ (CO₃)₆^6- + 3CO₃^3- are log K = -11,3; -10,0 and -8,8 respectively for M: U, Np, Pu. Then, polynuclear complexes can be efficient solution ''carriers'' for other hexavalent actinides in a waste disposal. Some properties of the solid phases MO₂CO₃(s) are discussed. Experimental studies of chemical equilibria of americium (III, IV) are reviewed: in carbonate media Am(III) species are Am CO₃⁺, Am (CO₃)₂^- Am (CO₃)₃^3-, (Am₂ CO₃)sub(s) and (NaAm(CO₃)₂)sub(s); for Am(IV), log B₅ approximately equal to 40. In NaClO₄ (3M) medium solubility measurements of Np(V) show that logβ₁ = 5,09, logβ₂ = 8,15, logβ₃ = 10,46, log Ks(Na Np O₂ CO₃) = 10,56 and log Ks (Na₃ NpO₂(CO₃)₂) = 12,44; ionic strength corrections are proposed

[en] Instrumentation has been developed to perform uv-vis-nir absorbance measurements remotely and at elevated temperatures and pressures. Fiber-optic spectroscopy permits the interrogation of radioactive species within a glovebox enclosure at temperatures ranging from ambient to >100 degree C. Spectral shifts as a function of metal- ligand coordination are used to compute thermodynamic free energies of reaction by matrix regression analysis. Pr³⁺ serves as a convenient analog for trivalent actinides without attendant radioactivity hazards, and recent results obtained from 20 degree--95 degree C with the Pr-acetate complexation system are presented. Preliminary experimentation on Am(3) hydrolysis is also described. 16 refs., 1 tab

[en] We have developed instrumentation capable of measuring optical absorption spectra over a wavelength range of 200--1200 nm and a temperature range of 20--100 degree C. This fiber-optic based spectrometer generates data which allow the computation of metal-ligand equilibrium constants. Studies at five temperatures have been completed using praseodymium-diglycolate as a model system. Fundamental thermodynamic values (free energies, enthalpies, entropies) were obtained from the experimentally-determined stability constants. Thermodynamic data pertinent to the interactions of actinides and long-lived fission products with groundwater, waste package components, and geologic media are critical input to modeling programs. 9 refs., 1 fig., 2 tabs

No abstract available

[en] Instrumentation has been developed to perform uv-vis-nir absorbance measurements remotely and at elevated temperatures and pressures. Fiber-optic spectroscopy permits the interrogation of highly radioactive species within a glovebox enclosure at temperatures ranging from ambient to > 100C. Spectral shifts as a function of metal-ligand complexation are used to calculate thermodynamic free energies of reaction by matrix regression analysis. The importance of such measurements to the perpetual confinement of the high-level nuclear waste is discussed, and recent results utilizing this technique are presented

[en] By spectrophotometric and potentiometric methods it is shown that trimers are formed in media of high ionic strength (3 M NaClO₄) and total concentrations of hexavalent actinides higher than 10^-3 M. The equilibrium constants for the reactions 3 MO₂(CO₃)₃^4- ↔ (MO₂)₃(CO₃)₆^6- + 3 CO₃^2- are lg K(U)=-11.3±0.1; lg K(NP)=-10.1±0.1; lg K(Pu)=-7.4±0.2. It is demonstrated that one of the cations of the trimer can be exchanged with another actinide cation: the equilibrium constants for the reactions 2 UO₂(CO₃)₃^4- + MO₂(CO₃)₃^4- ↔ (UO₂)₂MO₂(CO₃)₆^6- + 3 CO₃^3- are lg K=-11.3±0.1, -10.0±0.2 and -8.8 respectively for M=U, Np, Pu. Thus, polynuclear complexes can be efficient solution ''carriers'' for other hexavalent actinides in waste disposal. Some properties of the solid phases MO₂CO₃(s) are discussed. Experimental studies of chemical equilibria of americium (III, IV) are reviewed: in carbonate media americium(III) species are AmCO₃⁺, Am(CO₃)₂^-, Am(CO₃)₃^3-, (Am₂(CO₃)₃)₆ and (NaAm(CO₃)₂)_s; for americium-(IV) lg β₅ ≅ 40. In 3 M NaClO₄ solubility measurements of neptunium(V) show that lg β₁=5.09, lg β₂=8.15, lg β₃=10.46, lg Ks(NaNpO₂CO₃)=10.56 and lg Ks(Na₃NpO₂(CO₃)₂)=12.44; ionic strength corrections are proposed on the basis of these results. (orig.)

[en] The kinetics of ligand displacement reactions in the multicomponent system Tb/Humic acids/EDTA/Ca at pH 8.5 was studied by Time Resolved Laser Induced Fluorescence. The intensity of Tb(III) fluorescence was observed to increase upon binding to Humic Acids (HA), because of a non-radiative energy transfer between HA acting as luminescent donor and coordinated Tb ions serving as acceptors. Two kinetically distringuishable components of HA were identified. The rate of Tb mobilization with EDTA from the TbHA chelate was found to decrease considerably in the presence of Ca and with decreasing Tb concentrations. The rate determining steps of the reactions are the transformation of the mixed ligand complex intermediate Tb-EDTA-Ca and the Tb dissociation from the slower reacting component of HA. (orig.)

[en] The main task of a target producer is to make well characterized and homogeneous deposits on specific supports. Alpha and/or gamma spectrometry are traditionally used to monitor the quality of actinide deposits. With the increasing demand for enriched stable isotope targets, other analytical techniques, such as ICP-MS and NAA, are needed. This paper presents the application of neutron activation analysis to quality control of 'thin' targets, 'thicker' neutron dosimeters and 'thick' bronze disks prepared by the Reference Materials Unit at the Institute of Reference Materials and Measurements

[en] A series of reference materials intended for use as activation or fission monitors for neutron fluence rate measurements has been prepared by the Joint Research Centre of the European Commission. Certification has been carried out by expert European laboratories and distribution of the certified reference materials (CRMs) is through the BCR programme of the Commission. The list (18 CRMs) includes materials to cover the complete energy spectrum, and suitable for different irradiation times. Fission monitors are ²³⁸UO₂ or ²³⁷NpO₂ in the form of microspheres. Activation monitors are high purity metals (Ni, Cu, Al, Fe, Nb, Rh, or Ti), certified for interfering trace impurities, or dilute aluminium-based alloys, where aluminium is chosen as a suitable matrix for reducing the neutron self-shielding effect. Newly certified materials are IRMM-530R Al-0.1%Au, replacing the exhausted IRMM-530 material, used as comparator for k₀-standardization, and three new Al-Co alloys (0.01-1%Co). Two others, in the process of certification are Al-0.1%Ag and Al-2%Sc for thermal and epithermal fluence rate measurements. Other candidate reference materials currently being certified are two uranium-doped glass intended for dosimetry by the fission-track technique. (author)