Band 100, Heft 11 -

The data published on values of redox potentials E of heptavalent Np, Pu, Am, Ru and Mn and octavalent Ru and Pu were analyzed. The half-life ( τ 1/2 ) for reduction reactions of heptavalent metal by water in aqueous alkaline solutions was also analyzed. The decrease in the half life stability of actinide in water with the redox potential for 3− charged anions of Np(VII), Pu(VII), and Am(VII) was found. At the same potential, a charge decrease from 3− to 1−reduces the stability approximately two fold. For the redox couple Pu(VIII)/Pu(VII), the estimated value is E > 1.15  V/NHE. If Pu(VIII) existed as PuO 4 , it would be very unstable ( τ 1/2 ≈  × 10 2  s) in 1 M NaOH. For the anionic forms of Pu(VIII), PuO 4 (OH) 2 2− and PuO 6 4− , the half life was estimated to be very low ( τ 1/2 < 1 s).

A study of the electrochemical behaviors of N , N -dimethylhydroxylamine (DMHAN) and monomethyl hydrazine (MMH) in nitric acid solution on Pt electrodes were carried out by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) methods. The diffusion coefficients of DMHAN and MMH were obtained by CV. The values are found to be 0.53 × 10 6  cm 2 /s D (DMHAN ) and 0.88 × 10 5  cm 2 /s D (MMH ) . The equilibrium potentials (+0.47 V vs. SCE for DMHAN and +0.31 V vs . SCE for MMH) were also measured using Tafel curves. Various valence states of Pu and Np in HNO 3 solution containing DMHAN and MMH in the electrolytic process were investigated by an electrolytic cell using a platinum as the anode and a titanium plate as the cathode. In this procedure, MMH was first electro-oxidized on the Pt anode and Np(V) was reduced to Np(IV) on the Ti cathode. After MMH was entirely consumed, the accumulation of HNO 2 (due to the electrochemical reduction of nitric acid on the Ti cathode) caused a significantly fast catalytic reaction of DMHAN with HNO 3 to form HNO 2 . HNO 2 can oxidize Pu(III) to Pu(IV) quickly. As a result, both oxidation states of Pu and Np were found to be tetravalent in the post-electrolysis solution. A convenient method to keep the post-electrolysis solution at 70 ºC was used to adjust the oxidation state of Np in it's pentavalent state while retaining the tetravalent state of Pu. This study developed an electrolytic process for the preparation of 2AF feed (the feed of Pu purification cycle) in APOR (Advanced Purex Process Based on Organic Reductants) process by electrochemically oxidizing Pu(III) and selectively adjusting the valence state of neptunium to either Np(IV) or Np(V).

Crystal washing experiments were carried out using a uranyl nitrate solution in order to confirm the effect of uranyl nitrate hexahydrate (UNH) crystalline particle size on the removal of liquid impurities. The UNH crystal was immersed in a Ce solution and was washed for removing the mother liquor on the surface of the UNH crystals. Larger UNH crystals were advantageous for increasing the decontamination factors (DFs) of liquid impurities. The large crystal size reduced the specific surface area of the crystals which in turn decreased the adhesion of liquid impurities on the surface of the crystals. Therefore, high DFs of liquid impurities were achieved before and after washing. In the crystallization experiments, the DFs of metals for the UNH crystal were evaluated using a dissolver solution derived from irradiated fast neutron reactor core fuel. The UNH crystal size did not affect the decontamination of solid impurities such as Ba and Np even after crystal washing in the U crystallization experiments.

We measured the pH-dependent adsorption of Th(IV), an analogue for Pu(IV) and other tetravalent actinides, to two geomedia: goethite ( α -FeOOH(s)) and a heterogeneous Fe-containing sand from the southeastern USA. The goal was to examine whether or not the Th(IV)-goethite adsorption data could be used to predict the adsorption of Th(IV) by the heterogeneous sand. In the absence of either geomedia, after forty-eight hours the measured pH-dependent “adsorption” was consistent with the solubility of solid amorphous ThO 2 (am, aged), despite the fact that ThO 2 (am, aged) is generally not formed until approximately seventy days. We concluded that ThO 2 (am, aged) was stabilized by precipitating on the walls of the reaction vessels. Ignoring this phenomenon could lead to experimental artifacts in Th(IV) adsorption studies. Thorium adsorption by both goethite and the sand was strongly pH dependent, with adsorption increasing sharply from pH ∼ 2 to pH ∼ 4. Two methods were utilized to predict the pH-dependent adsorption of Th(IV) by the sand using the Th(IV)-goethite adsorption data. Using the Fe content of the sand and the Th(IV)-goethite adsorption data, we were able to predict the maximum amount of Th(IV) adsorption by the sand within 78% of the actual value ( i.e. , an error of 22%). In contrast, on a surface-area-normalized basis, we were only able to predict the maximum adsorption of Th(IV) by the sand within a factor of two. These results have important implications to scaling and extrapolating the results of batch-scale tetravalent actinide adsorption studies with pure minerals to predict their field-scale adsorption by and transport in heterogeneous subsurface media.

The present investigation entails the application of dry cow dung powder (DCP) as an indigenous, inexpensive and eco-friendly material for the removal of Cr(VI) from aqueous medium. Batch biosorption experiments were conducted employing 51 Cr(VI) as a tracer and the effect of various process parameters such as optimum pH, temperature, amount of resin, time of equilibration, agitation speed, concentration of metal ions and interfering effect of different salts etc. were studied. The kinetic studies were carried out employing various models but the best fitting was given by Lagergren Pseudo-second order model with high correlation coefficient R 2 value of 0.997 and adsorption capacity of 10.20 mg/g. The thermodynamic parameters for biosorption were evaluated as Δ G º = −2.837 kJ/mol, Δ H º = −4.757 kJ/mol and Δ S º = 16.64 J/mol K, which indicated spontaneous and exothermic process with high affinity of DCP for Cr(VI). Many naturally available materials are used for the biosorption of heavy metal pollutants, where most of them are physically or chemically modified. In this research work, DCP has been utilized without any pre or post chemical treatment. Thus it manifests the principle of green chemistry and proves to be an eco-friendly resin.

A typical high active waste (HAW) arising from reprocessing of the nuclear fuel –(U 0.3 Pu 0.7 )C irradiated to the burn-up of 155 GWd/Te in a Fast Breeder Test Reactor (FBTR) was characterized by various analytical techniques. The target element was separated from other interferences or pre-concentrated by a suitable technique such as solvent extraction, chromatographic methods etc. The results obtained from various techniques are compared. The implications of the estimated composition in handling, treatment and disposal of HAW are discussed.

For the decommissioning and disposal of shielding concrete from accelerator facilities, the Swiss Authorities require information on the radionuclide inventory. Besides the easy-to-measure γ -emitters 152 Eu, 60 Co, 44 Sc, 133 Ba, 154 Eu, 134 Cs, 144 Ce, 22 Na, also long-lived radionuclides emitting α - or β -radiation like 129 I, 10 Be, 36 Cl, 239/240 Pu and 238 U have to be studied in order to obtain an overview to which extent they are produced and whether they represent a safety issue. In this study, we present the chemical separation and determination of selected radionuclides in shielding concrete from two different positions in the accelerator facilities at the Paul Scherrer Institute (PSI), the BX2 station, which was shut down in 1998, and the environment of the target M station, where the samples were taken in 1985 during reconstruction. The results of the measurements show that in no case the radionuclide content represents a safety risk. The components can be decommissioned corresponding to the Swiss safety regulations.

Fast progressing immuno -PET gives reasons to develop new potential medium-long and long-lived radioisotopes. One of the promising candidates is 90 Nb. It has a half-life of 14.6 h, which allows visualizing and quantifying processes with medium and slow kinetics, such as tumor accumulation of antibodies and antibodies fragments or polymers and other nanoparticles. 90 Nb exhibits a high positron branching of 53% and an optimal energy of β + emission of E mean =0.35 MeV only. Consequently, efficient radionuclide production routes and Nb V labeling techniques are required. 90 Nb was produced by the 90 Zr( p,n ) 90 Nb nuclear reaction on natural zirconium targets. No-carrier-added (n.c.a.) 90 Nb was separated from the zirconium target via a multi-step separation procedure including extraction steps and ion-exchange chromatography. Protein labeling was exemplified using the bifunctional chelator desferrioxamine attached to the monoclonal antibody rituximab. Desferrioxamine was coupled to rituximab via two different routes, by the use of N-succinyl-desferrioxamine (N-suc-Df) and by means of the bifunctional derivative p -isothiocyanatobenzyl-desferrioxamine B (Df-Bz-NCS), respectively. Following antibody modification, labeling with 90 Nb was performed in HEPES buffer at pH 7 at room temperature. In vitro stability of the radiolabeled conjugates was tested in saline buffer at room temperature and in fetal calf serum (FCS) at 37 ºC. The selected production route led to a high yield of 145 ± 10 MBq/μA h of 90 Nb with high radioisotopic purity of >97%. This yield may allow for large scale production of about 10 GBq 90 Nb. The separation procedure resulted in 76–81% yield. The Zr/ 90 Nb decontamination factor reaches 10 7 . Subsequent radiolabeling of the two different conjugates with 90 Nb gave high yields; after one hour incubation at room temperature, more than 90% of 90 Nb-Df-mAb was formed in both cases. At room temperature in aqueous solution, both 90 Nb-Df-mAb constructs were more than 99% stable over a period of 18 d. The developed production and separation strategy provided 90 Nb with purity appropriate for radiolabeling applications. Labeling and stability studies proved the applicability of 90 Nb as a potential positron emitter for immuno -PET.