Band 100, Heft 12 -

We measured the 41 K thermal neutron absorption and resonance integral cross sections after the irradiation of KNO 3 samples near the core of the IEA-R1 IPEN pool-type research reactor. Bare and cadmium-covered targets were irradiated in pairs with Au-Al alloy flux-monitors. The residual activities were measured by gamma-ray spectroscopy with a HPGe detector, with special care to avoid the 42 K decay β - emission effects on the spectra. The gamma-ray self-absorption was corrected with the help of MCNP simulations. We applied the Westcott formalism in the average neutron flux determination and calculated the depression coefficients for thermal and epithermal neutrons due to the sample thickness with analytical approximations. We obtained 1.57(4) b and 1.02(4) b, for thermal and resonance integral cross sections, respectively, with correlation coefficient equal to 0.39.

Optical absorption spectra of Pu(IV) in 3 mol/dm 3 (M) nitric acid at 373 K were measured using an optical quartz cell equipped with a thin-film heater. Pu(IV) was oxidized to Pu(VI) by heating at 373 K, and the concentrations of Pu(IV) and Pu(VI) gradually decreased and increased, respectively, with the heating time. The ratio of Pu(IV) oxidized to Pu(VI) was 37% at a heating time of 394 min, and no Pu(III) or Pu(V) characteristic peaks were observed throughout the experiment. The oxidation rate of Pu(IV) in 3 M nitric acid at 373 K could be described by the equation -d [Pu(IV)] t /d t= k′ 1 [Pu(IV)] t -k′ 2 [Pu(VI)] t , where [Pu(IV)] t and [Pu(VI)] t were the concentrations of Pu(IV) and Pu(VI) at a heating time of t min. The apparent rate constants for Pu(IV) oxidation ( k′ 1 ) and Pu(VI) reduction ( k′ 2 ) at 373 K were calculated to be 2.3 × 10 3  min -1 and 3.4 × 10 3  min -1 , respectively.

Combination of sorption, desorption and kinetic experiments for Pu(IV) in silica and alumina suspensions over the pH range (2–9) have been employed to study the factors controlling Pu mobility from the near field of the repositories. These studies have been carried out using shorter lived isotope of Pu ( 238 Pu) thereby achieving Pu concentration ( ∼10 -9 M) near the solubility limit. Kinetic experiments were carried out to investigate the mechanism of the sorption process. In order to conclude about the surface speciation, desorption and leaching studies have been carried out on short as well as long time equilibrated sorption samples. Oxidation state transformation in the kinetic experiment was determined using parallelly carried out solvent extraction procedures. Silica was found governing the sorption at pH values ≲ 5.5 while both the surfaces quantitatively sorb the metal ion at higher pH values. The leaching and desorption experiments, in light of kinetic experiments, concluded the formation of small polynuclear Pu(IV) oxide/hydroxide species on both the surfaces. These experiments did not show any evidence for PuO 2 (am.) as the surface speciation. Oxidation state determination in silica supernatants revealed V as the oxidation state of Pu, while alumina suspensions favour higher oxidations state, i.e. , (VI) over (V) in the supernantant. Disproportionation of Pu(V) in the interfacial region, caused by the higher sorption affinity of alumina, produces Pu(VI) in the alumina supernatant. These findings provide new insight for defining the source term of Pu migration in geosphere.

Graft copolymers were prepared by 60 Co- γ irradiation of binary mixture of ethyl cellulose (EC) and acrylonitrile (AN). Conversion %-dose graphs were obtained, and 95% copolymer yield has been reached at around 8 kGy dose. Conversion of nitrile groups to amidoxime (AO) were achieved by aqueous solutions of NH 2 OH · HCl–NaOH at 50 ºC. The amidoxime conversion was followed by using FT-IR spectrophotometer and determined as percentage. After 72 h period, nearly 100% amidoxime conversion was provided. The structures of EC- g -AN and EC- g -AO were characterized by FTIR/ATR, TGA, and SEM methods.

Closing the nuclear fuel cycle in the US poses many challenges, one of which is found in the waste streams, which contain both trivalent lanthanides and actinides. The separation of americium from the raffinate will dramatically reduce the long-term radiotoxicity of the waste. The sorption of americium in both the tri- and pentavalent oxidation states was observed for four M(IV) phosphate-phosphonate ion exchange materials in nitric acid at pH 2. High selectivity was observed for reduced Am(III) with K d values ca . 6×10 5  mL/g, while the K d values for Am(V) were much lower. A new method of synthesizing and stabilizing AmO 2 + to yield a lifetime of at least 24 h in acidic media using a combination of sodium persulfate and calcium hypochlorite will be described.

The alkyl derivatives of diglycolamide (DGA) such as N , N , N ´, N ´-tetraoctyldiglycolamide (TODGA), N , N , N ´, N ´-tetraethylhexyldiglycolamide (TEHDGA) and N , N -diethylhexyl- N ´, N ´-dioctyldiglycolamide (DEHDODGA) are chain isomers differing only in the arrangement of carbon chain of the alkyl group. The extraction behavior of Am(III) in the solution of these diglycolamides in ionic liquid medium was studied as a function of concentration of nitric acid and diglycolamide. The results were compared with those obtained in a molecular diluent, n -dodecane. The extraction of Am(III) in ionic liquid medium increased in the order TEHDGA<TODGA< DEHDODGA, which was different from the customary trend of TEHDGA<DEHDODGA< TODGA obtained in n -DD. The anomaly observed in ionic liquid medium was probed by IR spectroscopy and measurement of stoichiometry. The stoichiometry of Am : DGA in each case was different and that exhibited a strong influence on the observed extraction trend. The unprotonated fraction of DGA, assessed from FTIR measurements, increased in the order TEHDGA<TODGA<DEHDODGA, which seems to be responsible for the observed anomalous extraction trend in DEHDODGA in ionic liquid medium.

Thulium-167, having a half-life of 9.25 d, is an important therapeutic radionuclide. It was produced via the nat Er( p , xn ) 167 Tm nuclear reaction by irradiation of a sedimented target with 15 MeV protons at a beam current of 20 μA. Radiochemical separation of 167 Tm from a solution of the irradiated erbium target in hydrochloric acid was performed using di-(2-ethylhexyl) phosphoric acid (HDEHP) in n -hexane and in chloroform separately. The effect of different molarities of HDEHP on extraction efficiency was investigated. The radiochemical yield of 167 Tm amounted to about 80 ± 5% while using n -hexane/HDEHP (1 M). The experimentally obtained production yield was about 3.2 MBq/μA h. It was comparable with the theoretical value of 4.1 MBq/μA h obtained from nuclear model calculations using the TALYS and EMPIRE codes.

Radiolysis in aqueous nitrate and acetic acid solutions and nitrate/nitric acid and phenol was studied. The radiolysis of these solutes occurs with • NO 2 radical, which is the active nitrating agent. Accumulation of nitromethane and nitrite was determined during γ -irradiation of aqueous solutions containing acetic and nitrate solutions. Irradiation of aqueous phenol–nitrate/nitric acid solutions results in the formation of 2- and 4-nitrophenols.

The adsorptive removal potential of Sr 2+ ions with titanate nanotubes (TNT) was investigated. Titanate nanotubes were synthesized via hydrothermal treatment of anatase titania powders and concentrated NaOH solution. Morphological and structural properties of titanate nanotubes were determined by XRD, BET and HRTEM. High resolution transmission electron microscopy (HRTEM) showed that uniform nanotubes with inner diameters of ≈ 4 nm and outer diameters of ≈ 12 nm were obtained. The adsorption behaviors of Sr 2+ ions on the TNT were also investigated. As a result of the experimental data, it was concluded that TNT are good adsorbents for the removal of Sr 2+ ions from aqueous solutions with an adsorption capacity reaching of 66.72 mg/g. The adsorption mechanisms of Sr 2+ ions from aqueous solutions onto TNT were examined with aid of model analyses of the adsorption equilibrium and kinetic data of Sr 2+ ions. The rate constant has been calculated for 288, 298, 308 and 318 K. Thermodynamic parameters for the sorption system have been determined.