C. Le Naour

Experimental verification of neutron phenomenology in lead and transmutation by adiabatic resonance crossing in accelerator driven systems

Energy and space distributions of spallation neutrons (from 2.5 and 3.57 GeV/c CERN proton beams) slowing down in a 3.3 x 3.3 x 3 m3 lead volume and neutron capture rates on long-lived fission fragments 99 Tc and 129 I demonstrate that Adiabatic Resonance Crossing (ARC) can be used to eliminate efficiently such nuclear waste and validate innovative simulation.

Structure of early actinides(V) in acidic solutions

Abstract Protactinium occupies a key position in the actinide series between thorium and uranium. In aqueous acidic solution, it is stable at oxidation state (V), occurring either as an oxocation or as a naked ion, depending on the media. Very few structural information on the hydration sphere of Pa(V) in acidic medium is available, in particular in hydrofluoric acid. Combined EXAFS and theoretical calculations have been used in this work to characterize the protactinium coordination sphere at various HF concentrations. The correlation of the XAFS data with quantum chemical calculations provides complementary structural and electronic models from ab initio techniques. At HF concentrations from 0.5 to 0.05 M, both theoretical calculations and EXAFS data suggest that the protactinium coordination sphere is mainly composed of fluoride ions. At the lowest HF concentration, the occurrence of a monooxo bond is observed with EXAFS, in agreement with the literature. A comparison of these data with related neptunium(V) and plutonium(V) diooxocations in perchloric acid is also presented.

Neutron driven nuclear transmutation by adiabatic resonance crossing

The use of accelerator driven system (ADS) like for instance the Energy Amplifier concept (EA) proposed by C. Rubbia and his group might be one of the solutions to solve the energy problem and in particular to answer the question: what could we do with the nuclear waste produced by the present nuclear reactors? We present in this paper the EA concept, which is illustrated by two experiments performed at the CERN-PS facility. One of them is the TARC (Transmutation by Adiabatic Resonance crossing) experiment which is designed to demonstrate the high efficiency offered by the EA to destroy the long-lived fission fragments.

Search for chemical separation of element 106 homologues in HF and HF-HCl media

Abstract In order to study the chemical properties of element 106 in aqueous media, fast, efficient and reproducible chromatographic separations were tested on its assumed homologues: Mo, W and U. Corroborative static and dynamic off-line experiments have shown that after fixation of these three elements on an anion-exchange resin in HF medium, selective elution could be achieved by using suitable concentrations of HCl-HF and HCl solutions. Separations of short-lived W isotopes, produced through heavy ion irradiation were also performed on-line.

Adsorption behavior of Zr, Hf, Nb, Ta and Pa on macroporous anion exchanger in NH4SCN/HClO4 and NH4SCN/HF media

The possible use of thiocyanate and ammonium thiocyanate-hydrofluoric acid mixtures for quantitative anion exchange separation of zirconium from hafnium and niobium from tantalum and protactinium has been investigated. Distribution coefficients of zirconium(IV), hafnium(IV), niobium(V), tantalum(V) and protactinium(V) on macroporous BIO-RAD AGMP1 resin over a wide range of SCN and SCN/HF concentrations have been determined. The simultaneous presence of these two complexing agents causes a strong decrease of the adsorption phenomena.

Transmutation of 99Tc in a low lethargy medium as a function of the neutron energy

In the TARC experiment the differential neutron flux φ(E,r) of a spallation of 2.5 and 3.5 GeV/c proton in large lead block is measured in the range between 0.1 eV and 1.5 MeV. A new technique, using small quantities (less than 0.1 gram) of material, is used for measuring the transmutation rate as a function of neutron energy in the range between 0.1 eV up to a few keV. The method is applied to a target of 86 mg (99Tc) mixed with 1.7 g of Aluminum. From these measurements the energy profile of the capture cross section can be extracted.

Molecular Characterization of Actinide Oxocations From Protactinium to Plutonium

This presentation addresses the structural characterization by EXAFS of actinide cations at oxidation states (V) and (VI) as one walks across the periodic table from Z = 91 (protactinium) to Z = 94 (plutonium). A structural comparison between Pa, U, Np and Pu oxocations in aqueous solution at formal oxidation states (V) and (VI) is carried out. These results are corroborated by quantum chemical and molecular dynamics calculations.

Complexation of protactinium(V) with nitrilotriacetic acid: a study at the tracer scale

Complexation of Pa(V) with nitrilotriacetic acid (NTA) in aqueous solution (1 M (Na,H)ClO4) was studied by solvent extraction at different acidities (pcH = 0.6; 1.0; 2.0 and 2.5) with the element at the tracer scale (CPa < 10−10 M). Two types of metal–ligand complexes were identified in solution: (1 : 1) and (1 : 2) complexes. The mean charge of the two successive complexes formed in aqueous phase was deduced from the variations of Pa distribution coefficient as a function of acidity. The apparent formation constants of PaO(NTA) and PaO(NTA)23− were also determined from the solvent extraction experiments. Capillary electrophoresis coupled with inductively coupled plasma mass spectrometry (CE-ICP-MS) experiments confirmed the charge −3 of the complex of maximum stoichiometry.

Neutron-induced fission cross section of {sup 234}U and {sup 237}Np measured at the CERN Neutron Time-of-Flight (n{sub T}OF) facility

A high-resolution measurement of the neutron-induced fission cross section of {sup 234}U and {sup 237}Np has been performed at the CERN Neutron Time-of-Flight facility. The cross sections have been determined in a wide energy range from 1 eV to 1 GeV using the evaluated {sup 235}U cross section as reference. In these measurements the energy determination for the {sup 234}U resonances could be improved, whereas previous discrepancies for the {sup 237}Np resonances were confirmed. New cross-section data are provided for high neutron energies that go beyond the limits of prior evaluations, obtaining important differences in the case of {sup 237}Np.A high-resolution measurement of the neutron-induced fission cross section of 234U and 237Np has been performed at the CERN Neutron Time-of-Flight facility. The cross sections have been determined in a wide energy range from 1 eV to 1 GeV using the evaluated 235U cross section as reference. In these measurements the energy determination for the 234U resonances could be improved, whereas previous discrepancies for the 237Np resonances were confirmed. New cross-section data are provided for high neutron energies that go beyond the limits of prior evaluations, obtaining important differences in the case of 237Np.

Molecular solids of actinide hexacyanoferrate: Structure and bonding

The hexacyanometallate family is well known in transition metal chemistry because the remarkable electronic delocalization along the metal-cyano-metal bond can be tuned in order to design systems that undergo a reversible and controlled change of their physical properties. We have been working for few years on the description of the molecular and electronic structure of materials formed with [Fe(CN)6]n- building blocks and actinide ions (An = Th, U, Np, Pu, Am) and have compared these new materials to those obtained with lanthanide cations at oxidation state +III. In order to evaluate the influence of the actinide coordination polyhedron on the three-dimensional molecular structure, both atomic number and formal oxidation state have been varied : oxidation states +III, +IV. EXAFS at both iron K edge and actinide LIII edge is the dedicated structural probe to obtain structural information on these systems. Data at both edges have been combined to obtain a three-dimensional model. In addition, qualitative electronic information has been gathered with two spectroscopic tools : UV-Near IR spectrophotometry and low energy XANES data that can probe each atom of the structural unit : Fe, C, N and An. Coupling these spectroscopic tools to theoretical calculations will lead in the future to a better description of bonding in these molecular solids. Of primary interest is the actinide cation ability to form ionic ? covalent bonding as 5f orbitals are being filled by modification of oxidation state and/or atomic number.