Volume 94, Issue 6-7 - NUCAR 2005

Recoil range distribution of evaporation residues formed in complete and incomplete fusion of 96 MeV 16 O with 93 Nb has been measured by recoil catcher technique followed by off-line gamma-ray spectrometry. The cross sections for complete and incomplete fusion were delineated from the earlier measured excitation function data at the same beam energy. The results show that incomplete fusion is associated with angular momentum values close to the critical angular momentum for complete fusion of the projectile and target.

The effect of temperature on the extraction behaviour of Am(III), Pu(IV) and U(VI) from nitric acid medium was studied employing N , N , N ′, N ′-tetraoctyl diglycolamide (TODGA) in n -dodecane. The two-phase equilibrium constants (log K ′ ex ) were calculated and compared with those of other extractants proposed for actinide partitioning, viz. octyl-(phenyl)- N , N -diisobutylcarbamoylmethyl phosphine oxide (CMPO) and N , N , N ′, N ′-dimethyl dibutyl tetradecyl malonamide (DMDBTDMA). Thermodynamic parameters, viz. Δ G , Δ H and Δ S for the extraction of actinides by TODGA were also compared with those of CMPO and DMDBTDMA. These studies indicate that the extraction processes of Am(III) and U(VI) are enthalpy driven whereas entropy factor counteracts the extraction. However, in the case of Pu(IV), the extraction process is enthalpy as well as entropy favoured. Role of diluent on the loading of Nd(III) in 0.1 M TODGA has also been investigated.

The extraction behaviour of Np(IV) by 3-phenyl-4-acetyl-5-isoxazolone (HPAI) was investigated from nitric acid medium in the presence of tri- n -octyl phosphine oxide (TOPO). Speciation studies, carried out by the slope analysis method, yielded binary species of the type Np(PAI) 4 when only HPAI was used as the extractant and ternary and quaternary species of the type Np(PAI) 4 ·TOPO and Np(PAI) 3 ·(NO 3 )·TOPO, respectively when both HPAI and TOPO were used together as the extractants. The two-phase extraction constant for the binary species (log k ex ) was calculated to be 8.44±0.05 while those for the ternary and quaternary species were found to be 12.84±0.22 and 11.26±0.07, respectively.

Third phase formation in the extraction of Th(IV) by tri-2-methyl butyl phosphate (T2MBP) in various diluents such as n -dodecane, n -tetradecane and n -hexadecane from nitric acid media has been investigated for the first time. The limiting organic concentration (LOC) and maximum organic concentration (MOC) as well as critical aqueous concentration (CAC) and saturated aqueous concentration (SAC) were measured as a function of equilibrium aqueous acidity. Data on LOC and MOC values have been generated with various concentrations of T2MBP (1.1 M, 1.38 M and 1.65 M) in n -dodecane at 303 K. LOC and CAC values have been measured for the extraction of Th(IV) by 1.1 M T2MBP/ n -hexadecane at various temperatures (298 K, 303 K and 313 K) as a function of equilibrium aqueous acidity. Effect of temperature on third phase formation has been studied in the extraction of Th(IV) from its solution with near zero free acidity by 1.1 M T2MBP in n -tetradecane and n -hexadecane as diluents. Data on extraction of nitric acid in the absence and presence of Th(IV) by T2MBP/ n -dodecane is also reported in this paper.

Extraction behaviour of some fission product contaminants like Zr(IV), RuNO(III), La(III), Ce(III) and Nd(III) with 1.1 M solutions of N , N -dihexyl octanamide (DHOA) and tri- n -butyl phosphate (TBP) in n -dodecane from nitric acid medium has been investigated under conditions prevailing in the PUREX process. Results of the study reveal that the extraction of Zr(IV), La(III), Ce(III) and Nd(III) with 1.1 M DHOA is significantly lower than that of TBP. However, the extraction of RuNO(III) with DHOA is of the same order as that with TBP. The influence of uranium(VI) saturation of the organic phase on the extraction of Zr(IV) and RuNO(III) is evaluated. The effect of degradation products of DHOA (caprylic acid/ n -dihexylamine) and TBP (di- n -butyl phosphoric acid) on the extraction of Zr(IV) is also examined. The study indicates the innocuous nature of the degradation products of DHOA towards the extraction of Zr(IV) under the PUREX process conditions. This is unlike the degradation products of TBP, the presence of which produce noticeable increase in the extraction of Zr(IV).

Membrane based non-dispersive solvent extraction (NDSX) of U(VI) from aqueous nitric acid medium was carried out using a commercial hollow fibre module containing microporous hydrophobic polypropylene capillaries. The NDSX operation was carried out by pumping U(VI) solutions at varying concentrations of nitric acid (1-5 M) through the tube side and organic solvent (di- n -hexyl octanamide (DHOA) in normal paraffin hydrocarbon (NPH)) through the shell side of the hollow fibre capillaries. Extraction studies were performed under different hydrodynamic conditions and the overall mass transfer was evaluated under counter-current flow conditions. Counter-current mode was found to be better as compared to the co-current mode. The U(VI) mass transfer rates were positively influenced by the nitric acid as well as DHOA concentrations.

Attempts were made to introduce four major fission products, namely, Cs, Sr, Ru and Te into thermodynamically stable NaZr 2 P 3 O 12 (NZP) ceramic, considered to be a viable alternative for fixation of high level nuclear waste (HLW), in place of borosilicate glass. The results showed that all these elements could be incorporated in NZP at temperatures as low as 723 K by heating the reaction mixtures in a microwave heating system. Among the four elements introduced in NZP, except for Te, all others were retained nearly quantitatively in samples heated to 1273 K for three hours. The tellurium substituted NZP exhibited the maximum loss exceeding the amount of TeO 2 added, which could probably be due to formation of some volatile compounds by TeO 2 with the elements in the NZP matrix. Addition of Sr and Te simultaneously in NZP decreased the amount of TeO 2 loss considerably.

Ceramic precursors of Zirconolite (CaZrTi 2 O 7 ) family have a remarkable property of substitution on Zr 4+ cationic sites. This makes them a potential material for nuclear waste management in ‘synroc’ technology. In order to simulate the mechanism of partial substitution of zirconium by tetravalent actinides, a solid phase of composition CaZr 0.9 U 0.1 Ti 2 O 7 was synthesized through ceramic route by taking calculated quantities of oxides of Ca, Ti and nitrates of uranium and zirconium, respectively. Solid-state synthesis was carried out by repeated pelletizing and sintering the finely powdered oxide mixture in a muffle furnace at 1050 °C. The polycrystalline solid phase was characterized by its typical powder diffraction pattern. Step analysis data were used for ab initio calculation of structural parameters. The SEM and EDAX analysis also confirm that the zirconolite acts as a host material for uranium. The powder diffraction data of 3500 points for 2θ=10°-80° has been analysed by GSAS (general structure analysis system) software to obtain the best fit of the observed data points. The uranium substituted zirconolite crystallizes in monoclinic symmetry with space group C2/ c (#15). The following unit cell parameters have been calculated: a =12.5615(13), b =7.2743(8), c =11.5103(33) and β=101.086(14). The calculated and observed values of the intensities, lattice parameters and density measurement show good agreement. The Rietveld analysis and GSAS based calculations for bond distance Ti-O, Ca-O, Zr-O, and O-M-O bond angles were made. The structure was refined to satisfactory completion. The Rp and Rwp were found to be 0.1583 and 0.2097 respectively. The crystal data of the title compound show that increase in U content results in expansion of the zirconolite unit cell.

Heavy ion Rutherford backscattering spectrometry, with 30 MeV 19 F beam, has been used to study the diffusion of cesium in borosilicate glasses of different compositions. The coefficient of cesium diffusion in borosilicate glass was obtained by analyzing the depth profile of cesium in samples annealed at different temperatures in the range of 100-350 °C. The activation energy of diffusion of cesium was found to be in the range of 9-22 kJ/mol, indicating the inter-diffusion between the cesium and sodium as the mechanism of the diffusion process. The activation energy was found to decrease with increasing sodium content of the glass, indicating that the alkali metal ion diffusion is governed by the interaction between the jumping ion and the dipole field around the oxygen ions.

Plasticized anion-exchange polymer inclusion membranes (PIM) were prepared by physical immobilization of a liquid anion-exchanger trioctylmethylammonium chloride (Aliquat-336) into the polymer matrix of cellulose triacetate (CTA) plasticized with 2-nitrophenyl octyl ether (NPOE). The self-diffusion coefficients ( D m ) of I − ion in these PIMs were obtained by analysing the experimental 131 I radiotracer exchange rates with an analytical solution of Fick's second law. The D m was found to increase exponentially as a function of volume fraction of liquid (plasticizer) in the membrane, which can be attributed to reduction of physical obstruction in diffusion path of the ions in CTA polymer matrix. The selectivity of PIMs towards different anions, with respect to I − ion, was obtained from a determination of mole fraction of I − ion (ratio of moles of I − ion to total ion-exchange sites) in the membrane as a function of mole fraction of I − ion in the equilibrating aqueous solution containing a competing X − ion (X − = F − /Cl − /Br − /NO 3 − /ClO 4 − ). This study indicated that the PIM has preference for I − ion in the presence of Cl − , Br − and NO 3 − ions in equilibrating solution, while ClO 4 − ion are preferred over I − ion. The selectivity trend (ClO 4 − >I − >NO 3 − >Br − >Cl − >F − ) in PIM was found to correspond with Hofmeister series.

A new class of polymeric resin called MCM-BEHSA, for extraction of U(VI), Th(IV) and La(III) was synthesized by grafting Merrifield chloromethylated polymer with N , N -bis-(2-ethyl-hexyl)-succinamic acid. The chemical modifications at each step of the grafting was confirmed by FT-IR spectroscopy, CPMAS solid state NMR spectroscopy, CHN elemental analysis and also by Thermo Gravimetric analysis. All the parameters influencing the quantitative metal ion extraction were optimized by both static and dynamic methods. The resin showed good extractability over a wide range of acidity (0.01-10 M) with fast exchange rate (saturation possible within 20 minutes) and high sorption capacities for U(VI), Th(IV) and La(III). Quantitative metal desorption was achieved by using 0.5 M (NH 4 ) 2 CO 3 for all the analytes. A significant feature of this grafted polymer was its ability to extract Th(IV) from very high nitric acid concentrations. Interference studies with commonly encountered metal ions, rare earth ions and electrolytes showed very high tolerance limit for those ions. Enrichment factor values of 400, 550 and 350 with limit of quantification (LOQ) as 10 ng ml -1 , 10 ng ml -1 and 20 ng ml -1 were observed for U(VI), Th(IV) and La(III), respectively. All the analytical data were within 3.2% rsd, reflecting the reproducibility and reliability of the developed method.

A simple and fast method for the dissolution of sintered ThO 2 and (U,Th)O 2 was developed. The products formed when these oxides were fused with ammonium sulphate at various temperatures were found to be readily soluble in dilute nitric acid. Among all the products obtained at various temperatures, (NH 4 ) 2 Th (SO 4 ) 3 and (NH 4 ) 2 (U x ,Th 1-x )(SO 4 ) 3 , obtained at 365 °C, were found highly soluble (>99%). After dissolution thorium was separated selectively by oxalate precipitation method. More than 95% of uranium was recovered from the solution by ammonium diuranate precipitation method. The products formed at different temperatures were characterised by X-ray, thermal and chemical analysis techniques.

The presence of organic complexants, such as α-isosaccharinic acid (ISA) in an intermediate-level radioactive-waste (ILW) repository may have a detrimental effect on the sorption of radionuclides by forming organic complexes in solution. To assess this, stability constants are required for the complexes formed. Constants have been determined for the divalent metal ions, Cd 2+ , Co 2+ and UO 2 2+ with α-isosaccharinic acid (ISA) in near-neutral and alkaline conditions. The effect of these complexes on radionuclide solubility in the near-field and alkaline-disturbed zone is shown. The constants were measured by the ion-exchange (Schubert) method [1] with the exception of U(VI) at pH 13.3, for which the solubility product method [2] was used. At pH7 each complex was of the form M 1 ISA 1 , with log β values suggestive of salt formation. At high pH, log β values were between 13 and 20. The number of hydroxide ions involved in the complexation reactions was determined using Bjerrum plots, conductometric titrations and spectrophotometric methods [1]. The constants have enabled speciation calculations to be performed showing the effect of ISA on the metal's solubility. Solubility is predicted to increase in the presence of ISA from pH 9 to 13.5, suggesting that it may have an impact on radionuclide behaviour. The largest solubility increases are for Cd and Co, the smallest for U(VI).

Effect of humic acid (HA) on the sorption behaviour of 137 Cs on silica colloids has been studied by batch procedure over a pH range of 3-10 and at ionic strength of 0.05 M (NaClO 4 ). The sorption of 137 Cs on bare silica colloids was found to be negligible up to pH 7 above which it was found to increase sharply with pH. In the presence of HA significant enhancement in the sorption of 137 Cs on silica colloids was observed at lower pH values with no effect at pH > 7. Zeta potential of the colloidal suspension of HA, silica and their binary mixture were also measured. Binary interaction between 137 Cs and HA, and that between HA and silica were investigated in order to explain the observations in terms of linear additive model. The data obtained in the present work confirmed the role of non-additive factors in the ternary sorption system.

The preparation and preliminary biological evaluation of a metronidazole-BFCA (bifunctional chelating agent) conjugate labeled with 177 Lu is reported. Metronidazole, a well known hypoxia marker has been suitably derivatized and coupled with a polyazamacrocyclic BFCA, namely, para-aminobenzyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid ( p -amino-benzyl-DOTA). 177 Lu, which is presently being considered as one of the pivotal radionuclides for targeted therapy was produced in adequate specific activity (∼185 TBq/g) and high radionuclidic purity (99.99%) by irradiating enriched (60.6% 176 Lu) Lu 2 O 3 target at a moderate thermal neutron flux of 3×10 13 n/cm 2 /s. The metronidazole-BFCA conjugate was radiolabeled with 177 Lu in high radiochemical purity (97%). Preliminary biodistribution studies carried out in Swiss mice bearing fibrosarcoma tumors revealed good tumor uptake (1.30% ID/g at 30 min post-injection) with rapid renal clearance (94.48% ID at 30 min post-injection) and significant tumor to blood (28.00 at 3 h post-injection) and tumor to muscle (14.00 at 3 h post-injection) ratios.