Volume 94, Issue 1 -

Systematic studies on fission neutron spectrum averaged cross sections of some threshold reactions like ( n , p ) and ( n ,α) on cadmium were carried out using the activation technique in combination with radiochemical separations and high-resolution γ-ray spectroscopy. Special attention was paid to the formation of 103 Pd via the 106 Cd( n ,α) 103 Pd reaction since it is an important therapeutic radionuclide. At a fast flux neutron density of 7.5 × 10 13 cm 2 s -1 and an irradiation time of 120 h, using 100% enriched 106 Cd target 340 MBq of no-carrier-added 103 Pd per batch could be produced. The method is thus suitable for medium-scale production of this radionuclide.

Several ruthenium species compounds are typically encountered in waste management from nuclear fuel reprocessing operations. Ozone acting as a strong oxidizing agent in aqueous alkaline medium presents some advantages to dissolve rapidly solid deposits of RuO 2 , x H 2 O formed into process devices, without generating troublesome byproducts or secondary wastes. In this study, a three-phase solid-gas-liquid column was used for dissolution experiments where the ozone gas flow was contacted with RuO 2 , x H 2 O solid particles suspended in sodium hydroxide solution. The analysis of reaction by-products, ruthenate and perruthenate ions, leads us to propose a reaction mechanism. It points out the autocatalytic effect of ruthenate RuO 4 2- in the dissolution reaction mechanism. Parametric experimental study has been performed. It shows that increase of oxidative dissolution kinetics is obtained: (i) with a particular RuO 2 , x H 2 O solid morphology, (ii) for an optimum sodium hydroxide concentration near 0.5 M, (iii) by increasing gas-liquid exchange surface area, (iv) by increasing ozone concentration in the gas and (v) by increasing ruthenium initial concentration.

Oxidation of the nitrosyl ruthenium complex RuNO(OH) 5 2- has been carried out in sodium hydroxide solutions in contact with a gas flow containing ozone. The RuNO(OH) 5 2- complex is converted successively into ruthenate and perruthenate ions. An empirical kinetic rate law for the first step has been determined and was shown to depend on concentrations of (i) the ruthenium complex, (ii) the hydroxide ions and (iii) ozone concentration in the gas flow. The second step of the reaction, corresponding to the perruthenate ion formation, shows a complex mechanism and four competing reactions have been proposed to represent it. The influences on the second step kinetics of several parameters such as ozone or hydroxide concentrations or the conditions of the gas-liquid exchange area are also qualitatively discussed.

The o-carboxy N - N ′-dimethylbenzylamine uranium(VI) and thorium(IV) complexes, o-C 6 H 4 COOHCH 2 N-(CH 3 ) 2 UO 2 SO 4 (I), o-C 6 H 4 COOHCH 2 N(CH 3 ) 2 UO 2 (NO 3 ) 2 (II), o-C 6 H 4 COOHCH 2 N(CH 3 ) 2 UO 2 Cl 2 (III), and o-C 6 H 4 CO-OHCH 2 N(CH 3 ) 2 Th(NO 3 ) 4 (IV) were prepared and studied by means of thermoanalytical techniques in static air atmosphere to understand their mode of decomposition and thermal stability. Their compositions were investigated by elemental analysis in order to ensure their purity, and structure elucidations were based on proton NMR and IR spectra. Study of their thermal decomposition showed that they pyrolyzed in stages: the degradation of square bipyramidal complexes (I and III) occurred in four stages; hexagonal bipyramidal complex (II) also followed the same pattern. The decomposition of bicapped square antiprism complex (IV) proceeded in three steps. The thermal decomposition of these complexes occurred with the loss of inorganic and organic fragments and exhibited almost the same mode of decomposition. The composition of the intermediate formed during degradation was confirmed by microanalysis and IR spectroscopy. The residue after heating above 480 °C corresponded to metal oxide. It follows from the results that the thermal stability of the complexes increases in the following sequence: Complex II, Complex IV < Complex III < Complex I

Ni radioisotopes are present in cementitious repositories for radioactive waste and considered to be safety relevant in performance assessment. The behaviour of non-radioactive nickel and 63 Ni in cement systems has been investigated in batch-type experiments under conditions corresponding to the initial stage of cement degradation. Solubility tests using 63 Ni labelled solutions mixed with an artificial cement pore water (ACW) at pH 13.3 revealed that a Ni-containing precipitate was formed at high Ni concentrations, which limits the concentration of dissolved Ni to (2.9 ± 0.5) × 10 -7 M. The concentration of dissolved Ni in cement suspensions, however, was controlled by the partitioning of non-radioactive Ni between the hardened cement paste (HCP) and ACW. The concentration of dissolved Ni was found to be independent of the solid-to-liquid (S/L) ratio in the range between 10 -6 kg L -1 and 0.13 kg L -1 ((7.3 ± 3.9) × 10 -8 M). The concentration of dissolved Ni could not be modelled on the assumption that Ni partitioning is a reversible linear sorption process. The experimental data and the modelling indicate that a solubility-limiting process controls the concentration of dissolved Ni in the cement systems. Measurements of the sorption isotherm showed only a small increase in the concentration of dissolved Ni from about 5 × 10 -8 M to about 8 × 10 -7 M while the concentration of added Ni varied over several orders of magnitudes (10 -6 M–5 × 10 -2 M). This finding supports the idea that a solid-solution aqueous-solution system involving Ni may account for the behaviour of Ni in cement systems. The distribution ratio for the partitioning of 63 Ni between HCP and ACW was found to be consistent with literature data obtained under similar experimental conditions ( R d =0.15 ± 0.02 m 3 kg -1 ). The R d value determined on Ni loaded HCP samples (3.9 × 10 -4 mol kg -1 and 4.3 × 10 -3 mol kg -1 ) increased with increasing Ni concentration in HCP. It is shown that the uptake of 63 Ni can be interpreted in terms of an isotopic exchange process with the non-radioactive Ni of the cement matrix. The distribution coefficient, α, of the exchange process ranges in value between about 0.02 and about 0.06, indicating that only a small portion of the Ni inventory is accessible to isotopic exchange.

A method combining radioactive ‘multitracer’ and dialysis techniques was developed to study the binding of multiple metal ions to humic acid (HA). Technical problems such as the leakage of small-molecule HA segment and the slow diffusion of metal ions through the dialysis membranes were examined. Under the condition of pH = 4.0, I = 0.100 M NaNO 3 , [Mg II ] = 0 M, or [Mg II ] = 0.500×10 -3 M, the interactions between Inogashira humic acid and metal ions (Be II , Sc III , Zn II , Co II , Mn II and Sr II ) were investigated by varying the metal concentrations in a wide range. It was found that as the concentrations of the trace metals are significantly smaller than that of HA, there are abundant binding sites available and there are no competition interactions between the trace metal ions of interest. Therefore, the stability constants for multiple metal ions binding onto humic substances can be obtained readily using the present method. The method is useful for quickly determining trace metal binding onto humic substances in environmental chemistry.

A new assay method was developed to determine added stable caesium (Cs) in blood plasma. The simple and inexpensive method is based on the competition between stable and radioactive Cs in binding to ammonium-iron(II)-hexacyanoferrate(III) (AFCF), followed by the precipitation of AFCF-bound Cs with plasma proteins, and the measurement of the radioactivity of the precipitate. For data treatment, standard procedures of radioimmunoassay were used. At present stage, the qualitative detection limit is around 0.2 μmol L -1 , and the practical limit for quantitative results around 1 μmol L -1 . The method is applicable only for recently added Cs in blood plasma, and cannot be used to measure endogenous plasma Cs or Cs in other tissues. Determining plasma kinetics of Cs might be useful in the study of some aspects of potassium kinetics, since these two alkali metals are transported into cells by the same cellular mechanism (Na,K-ATPase).

In a previous study, the sorption of radiocobalt by powdered pottery materials was investigated. The use of these materials as immobilization matrix for liquid radioactive waste requires the employment of pottery vessels. Therefore, the present study aims to give detailed investigations of the decontamination of radionuclides and toxic elements using pottery containers. These investigations are equally useful to elucidate how far these vessels can be utilized for water purification through decontamination of toxic and heavy metals. The radionuclide or heavy metal removal capability using pottery pots, as low cost sorbents, has been investigated for both radioactive ( 203 Hg) and stable mercury. The results indicated that Hg 2+ is better removed by pottery from neutral to alkaline solutions. The capacity of the used pottery container (100 ml in volume) for complete removal of mercury was found to reach 3 × 10 -4 mol/l, and the time needed was 8 hours. The sorption process was suggested to occur via adsorption and ion exchange. The effect of presence of humic or fulvic acid, as ligands abundant in water, is also investigated. The results imply that, in absence of humic or fulvic acid the sorption follows the expected behaviour, i.e. sorption sites with similar affinity for mercury. In presence of humic or fulvic acid, additional sorption sites are available by the organic molecule when it is associated to the pottery.

The extraction of Bk(III) into an organic phase consisting of 2,6-bis-(benzoxazolyl)-4-dodecyloxylpyridine, 2-bromodecanoic acid and tert-butyl benzene as a function of nitrate ion concentration in the aqueous phase was studied in order to determine the stability constants of the formation of Bk nitrate complexes. Increasing the nitrate ion concentration in the aqueous phase will increase the nitrate complex formation and thus the extraction of metal ions will decrease. Measuring this decrease in distribution ratio and fitting the data points with an appropriate model gives the stability constants of the Bk nitrate complex formation.