Volume 97, Issue 8

The formation of aqueous Cm(III) nitrate complexes is studied in the temperature range from 5 to 200 °C by time resolved laser fluorescence spectroscopy (TRLFS). The experiments are performed in a custom build high pressure and high temperature fluorescence cell. The complex formation is measured at nitrate concentrations ranging from 0.10 to 4.61 mol/kg H 2 O. The mono- and dinitrate complexes are quantified by peak deconvolution of the fluorescence spectra and the complexation constants are determined as a function of the temperature. The conditional equilibrium constants are extrapolated to zero ionic strength using the specific ion interaction theory (SIT) and the thermodynamic standard state data (Δ r H ° m , Δ r S ° m , Δ r G ° m , Δ r C ° p,m ) are determined from the temperature dependence of the equilibrium constants at I =0. The equilibrium constants up to 75 °C are well described by the Van´t Hoff equation (Δ r H ° m independent of T and Δ r C ° p,m =0). Modelling of the data at higher temperatures requires an extended equation including a term for the heat capacity changes (Δ r C ° p,m ).

A rapid procedure for the determination of Am, Pu, Th and U radionuclides in soil and sediment samples is described that can be used for environmental monitoring in emergency situations. The method is based on the fast and complete destruction of small amounts (up to 0.5 g) of samples by lithium metaborate fusion, followed by pre-concentration of the actinides by co-precipitation with calcium fluoride in acidic solution, and separation of the actinides by selective extraction chromatography using a single column filled with TRU resin. Am, Pu and Th are stripped separately, while U and Np are stripped together. Alpha sources are prepared from the chromatographic strip solutions directly by micro-co-precipitation with neodymium fluoride. Activities are determined by means of isotope dilution alpha spectrometry. The method provides accurate and reliable results for the activity concentrations of elevated levels of 239,240 Pu, 238 Pu, 241 Am and natural levels of Th nuclides in soil and sediment samples in course of 24 h. By further purification U and Np nuclides can be separated and determined, too.

Volatile metal complexes of the group 4 elements Zr and Hf with hexafluoroacetylacetonate (hfa) have been studied using short-lived radioisotopes of the metals. The new technique of physical preseparation has been employed where reaction products from heavy-ion induced fusion reactions are isolated in a physical recoil separator – the Berkeley Gas-filled Separator in our work – and made available for chemistry experiments. Formation and decomposition of M(hfa) 4 (M=Zr, Hf) has been observed and the interaction strength with a fluorinated ethylene propylene (FEP) Teflon surface has been studied. From the results of isothermal chromatography experiments, an adsorption enthalpy of -Δ H a =(57±3) kJ/mol was deduced. In optimization experiments, the time for formation of the complex and its transport to a counting setup installed outside of the irradiation cave was minimized and values of roughly one minute have been reached. The half-life of 165 Hf, for which conflicting values appear in the literature, was measured to be (73.9±0.8) s. Provided that samples suitable for α-spectroscopy can be prepared, the investigation of rutherfordium (Rf), the transactinide member of group 4, appears possible. In the future, based on the studies presented here, it appears possible to investigate short-lived single atoms produced with low rates ( e.g. , transactinide isotopes) in completely new chemical systems, e.g. , as metal complexes with organic ligands as used here or as organometallic compounds.

A biamperometric method is described for the determination of uranium in plutonium bearing nuclear fuel materials. Ti(III) is used for reducing U(VI) to U(IV) in 6 to 9 M H 2 SO 4 medium, followed by destruction of the excess reductant by HNO 3 . Plutonium is also reduced to Pu(III), but is selectively oxidized to Pu(IV) by the HNO 2 produced in situ during the destruction of the excess Ti(III) by HNO 3 . The U(IV) is determined by titration with standard K 2 Cr 2 O 7 . Accuracy and precision of the method have been evaluated using different amounts of uranium ranging from 5 microgram to 20 milligram. The method has been applied to U determination in uranium oxides, uranium carbides, (U,Pu)O 2 , (U,Th)O 2 , (U,Pu)C and U-Al alloy. The method has also been employed for the determination of U present at very low levels (<0.2%) in PuO 2 .

In order to contribute to the long-term safety analysis of direct disposed research reactor fuel elements, the corrosion behavior of these fuel-types in final repository relevant salt brines was determined. Due to the corrosion processes, radionuclides were mobilized first, but then trapped by the formed secondary phases. A Mg-Al layered double hydroxide (LDH) with chloride as interlayer anion was identified as one crystalline secondary phase component. The possibility to incorporate zirconium-IV into the lattice structure of the Mg-Al-Cl LDH was investigated by a co-precipitation process. The element zirconium was chosen because it has a low absorption cross section for neutrons, and is therefore used for nuclear energy applications, such as for cladding fuel elements. No zirconium release was detected, when the obtained LDH was treated with an ammonium carbonate solution. The molar stoichiometry with respect to Mg, Al and Zr remained stable and this is the first indication for the incorporation of zirconium. For further examination, the material was analyzed by powder X-ray diffraction (XRD) combined with a Rietveld refinement. Due to a recursive calculation inside the Rietveld refinement, it was possible to derive structural parameters of the disordered LDH. Further on, the Mg-Al-Zr-LDH was analyzed by EXAFS and the results did show that Zr is the central metal atom coordinated by 5 OH groups and by one chloride.

Radiation and chemical stabilities of CMPO-functionalised calix[4]arenes, promising ligands for extraction of actinides and lanthanides, were studied both in solution and in the solid state. A comparison of the results showed that the degradation of ligands under radiolytic conditions proceeds indirectly via interactions with the solvent. The radiation stabilities in chloroform and 1-octanol were systematically studied using model compounds, and the main degradation product under extraction conditions (organic phase/conc. HNO 3 ) was characterised.

An approximate comparison of neodymium sorption at pH=1.5, between the well studied Saccharomyces cerevisiae and three other related microorganisms ( Kluyveromyces marxianus , Candida colliculosa and Debaromyces hansenii ) was made. Although big differences were not observed, a slightly higher neodymium uptake was attained by the latter three kinds of yeasts. Their adsorption isotherms, varying the initial metal concentration from 10 to 200 mg/L, at constant ionic strength ( I =0.1 mol/L), could be fitted equally well, either to Langmuir or Freundlich adsorption model. Their estimated values of q max and K f , which are related to adsorption capacity, ranged from 10−12 mg/g and 0.90–1.2 respectively. The corresponding Scatchard plots suggest two types of bonding sites for all yeast studied and common receptor sites between C. colliculosa and D. hansenii . It is also discussed, the feasibility of using all these microorganisms, as potential detoxification tools, wherever contamination of foodstuffs by radionuclides, seems to be probable.

A novel method has been developed for the controlled delivery of various ligands including solid extractants using supercritical carbon dioxide (Sc-CO 2 ). A ligand delivery vessel with a restricted geometry where its inlet and outlet are located beside each other, accomplished the task of the controlled delivery of ligands. The proposed method eliminates the usage of modifier solvent such as methanol for the delivery of various ligands during the supercritical fluid extraction of metal ions. Using neat Sc-CO 2 , the delivery profiles for the various ligands such as octyl(phenyl)- N , N -diisobutylcarbamoylmethyl-phosphineoxide (CMPO), tri- n -butyl phosphate (TBP), tri- n -octyl phosphine oxide (TOPO), theonyltrifluroacetone (TTA) and di(2-ethylhexyl)isobutyramide (D2EHIBA) were established. The delivery profiles were optimised by investigating the influence of various extraction parameters such as ligand delivery vessel geometry, temperature, pressure, flow rate of Sc-CO 2 and ligand content. Applications of these ligand delivery modes were demonstrated for the supercritical fluid extraction of uranium from tissue paper matrix and preferential extraction of uranium over thorium. These results are compared with the extraction studies involving methanol or hexane modifier under similar experimental conditions. The extraction of neodymium nitrate was also demonstrated using modifier free delivery mode.

129 I is preconcentrated from environmental samples and its accessibility is addressed for inductively coupled plasma quadrupole mass spectrometer with collision/reaction interface (ICP-CRI-QMS). By applying oxygen as CRI gas through skimmer cone, the signal of the interfering 129 Xe from the impurity of plasma gas can be eliminated while the formation of 127 I 1 H 1 H + can be partially removed. The improved ICP-QMS can be employed for investigation of 129 I in environmental samples with a 129 I/ 127 I ratio down to 10 -7 . The detection capability was demonstrated by measuring 129 I in seaweed samples collected around the nuclear fuel reprocessing plant at La Hague. The abundant 127 I in the sample matrix causes a serious problem and degrades the detection capability of the instrument when the concentration of 127 I is larger than 10 5  ng/g. Even combined with a sufficient pre-concentration procedure, ICP-QMS is not considered as a suitable technique for the analysis of 129 I in uncontaminated environmental samples with 129 I/ 127 I ratio of less than 10 -7 . Results are presented for seaweed samples collected around La Hague. In addition, time dependant I concentrations and ratios are given for colloids and water sampled from Lake Thun.

In order to evaluate the potential incorporation of 129 I into uranyl phases that would form during oxidative alteration of spent nuclear fuel, uranophane was synthesized under mild hydothermal conditions of 165°C in the presence of iodide, iodate and periodate, respectively. The precipitates were examined and analyzed using powder X-ray diffraction (XRD), infrared spectroscopy (IR) and scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS). The results indicate that significant amount iodine can be incorporated into the structure of uranophane in the form of IO 4 - , and less in the form of IO 3 - . Crystallo-chemical analyses suggest that the incorporation mechanisms would be the substitution of iodate and periodate for SiO 4 tetrahedron in the sheet.