Volume 108, Issue 11

A series of single stage trials were conducted using six reducing reagents to investigate the rate determining step during Np(VI) reduction back-extraction from 30%TBP/Kerosene to HNO 3 solution under the same conditions. The six reducing reagents included: acetohydroxamic acid, N,N -dimethylhydroxylamine, N,N -diethylhydroxylamine, 2-hydroxyethylhydrazine, methylhydrazine and N,N -dimethylhydrazine. Moreover, the back-extraction of Np(V) from 30%TBP/Kerosene to HNO 3 solution without reducing reagent was conducted with the same concentrations of Np and HNO 3 . The experimental results indicate the rate of Np(VI) reduction in the two-phase system is determined mainly by the rate of Np(V) mass transfer from 30%TBP/Kerosene to HNO 3 solution, whose mass transfer kinetics is far slower than previously estimated. The rate determining step is a slow chemical reaction as: NpO 2 NO 3 ·TBP = NpO 2 +  + NO 3 −  + TBP.

In the suitability assessment of candidate materials as engineering barriers for a Deep Geological Repository (DGR), new studies concerned with zirconium silicate have been carried out. The zirconium silicate extracted from beach sand, was submitted to gamma irradiation in order to evaluate its structural stability and then functionalized with phytic acid (IP6) and measured its sorption capacity vis-a-vis uranium. The purified, irradiated and functionalized material was then characterized by several analytical techniques. The surface parameters including the surface area and density of surface sites were also determined. The results obtained from physic-chemical characterization showed that there were no significant changes in the structure of zirconium silicate after its gamma-irradiation. These results are consistent with those of sorption experiments. Uranium (VI) sorption capacity of zirconium silicate is increased in the presence of phytic acid and remained constant after its exposition to high doses of gamma-radiation (10 and 30 MGy). These results show that the IP6-functionalized zirconium silicate can be used as engineering barriers for a DGR.

In the present study, the nature of Eu(III) complexes (Eu(III) was used as a surrogate for Am(III)) formed in kaolinite–humic acid (HA)/citric acid (CA) system was investigated by luminescence spectroscopy. In addition to the ternary system (kaolinite + Eu + L(CA/HA)), the binary system (Eu-L) was also looked at for a better understanding of the complexes formed at the kaolinite surface. The lifetime and emission spectra of Eu-L complexes on the kaolinite surface differ considerably as compared to the same in the aqueous phase. The Eu-HA aqueous complexation shows differences in the excitation spectra with similar decay lifetimes with increasing aqueous HA concentrations. The ligand-to-metal charger transfer (LMCT) in the Eu-HA excitation spectra suggests the complexation of Eu(III) with HA at pH ∼ 4. Although the mode of Eu(III) binding to the kaolinite surface in the presence of CA/HA was the same i.e. metal-bridged ternary complex formation, the local surroundings around the sorbed Eu(III) differ in the two cases. The loading of HA in the Eu-HA-kaolinite system does not have a large effect on the local structure around the sorbed Eu(III) ion, but enhances the percentage of Eu(III) uptake onto the kaolinite surface. The number of H 2 O molecules in the primary hydration sphere of sorbed Eu(III) differs in the Eu-HA-kaolinite and Eu-CA-kaolinite systems. In addition, Eu(III) assisted precipitation of HA was also seen using a radiometric method.

Sorption distribution coefficient (Kd) of niobium-94 on minerals are an important parameter in safety assessment of intermediate-depth disposal of waste from core internals etc. The Kd of Nb on clay minerals in Ca(ClO 4 ) 2 solutions were, however, not successfully modeled in a previous study. The high distribution coefficients of Nb on illite in Ca(ClO 4 ) 2 solutions were successfully reproduced by taking Ca–Nb–OH surface species into account. Solubility of Nb was studied in Ca(ClO 4 ) 2 solutions and the results were reproduced by taking an aqueous Ca–Nb–OH complex species, CaNb(OH) 6 + , into account in addition to previously reported Nb(OH) 6 − and Nb(OH) 7 2− . Based on this aqueous speciation model, the Ca–Nb–OH surface species responsible for the sorption of Nb on illite in Ca(ClO 4 ) 2 solutions was presumed to be X_OCaNb(OH) 6 . Although uncertainties exist in the speciation of aqueous Ca–Nb–OH species, the result of this study proposed a possible mechanism for high distribution coefficient of Nb on illite in Ca(ClO 4 ) 2 solutions. The mechanism includes Ca–Nb–OH complex formation in aqueous, solid and surface phases.

The quantity of liquid organic radioactive wastes produced by the use of radioactive materials in nuclear research facilities is small compared to aqueous radioactive waste, but a special and low-cost treatment method is needed. Here we investigated the adsorption performance of five materials, namely: KU-2 resin, bentonite, charcoal (M&S) and clay adsorbents for the successful removal of 90 Sr/ 90 Y from liquid scintillation cocktail waste. The batch adsorption technique (influence of pH, contact time, and temperature), sequential, and column technique were investigated. The efficiency of these adsorbents for the removal of 90 Sr/ 90 Y is in this order, resin > bentonite > clay with removal efficiency 90 ± 5.2, 68 ± 3.25, and 65 ± 5.3%, respectively. While charcoal has lower affinity for the sorption processes. Purification of liquid scintillation (LS) cocktail by separation of 90 Sr/ 90 Y was successfully carried out by packed column with KU-2 resin. The exhausted loaded column with 90 Sr/ 90 Y is successfully regenerated by 25 mL, 1 M HNO 3 . Characterizations of the original and the purified LS cocktail were carried out using FTIR analysis. The efficiency of the purified liquid scintillation waste (LSW) for the determination of radionuclide is about 62.67 ± 4.8.

Radiolytic stability of pillar[5]arene-based diglycolamides (P5DGAs) against gamma irradiation up to 1000 kGy adsorbed dose was studied. The results reveal the increase of radiation damage degree on P5DGAs with dose. The radiolysis products of P5DGAs including the gaseous and solid products were fully characterized by 1 H NMR, HR-ESI-MS, GC, and HPLC techniques. It was found that the main radiolytic gas products of P5DGAs under argon are H 2 , N 2 , CO and gaseous hydrocarbons. The solid degradation products contain phenolic hydroxyl groups and secondary amine groups. In addition, solvent extraction toward Eu(III) was performed with P5DGAs, in which about 50% decrease on extraction efficiency was observed for irradiated P5DGAs with dose of 1000 kGy in comparison with the non-irradiated one. A radiolytic degradation pathway was also proposed based on the above results. This is the first time to investigate the radiolytic stability of neat P5DGAs and P5DGAs in molecular diluent in detail and provides useful information for further application of P5DGAs in practical applications for spent fuel reprocessing.

Samples of Egyptian monazite ore obtained from black sand of Abu-Khashaba, Rashied (Rosetta) area on the Mediterranean Sea coast were analyzed for some lanthanides and coexisting elements using instrumental neutron activation analysis (INAA). The analyses were carried out qualitatively and quantitatively for the elements Ce, Nd, Eu, Gd, Tb, Yb and Sc, La as well as the accompanying elements Co, Cr, Fe, Hf, Nb, Zn, Zr in addition to the actinides Th and U; whereas after relatively longer decay time the following lanthanide elements were analyzed: Ce, Nd, Eu, Gd, Tb, Yb and Sc, beside the accompanying elements Co, Cr, Fe, Hf, Nb, Zn, Zr and Th. Two certified reference materials (CRM) were used in this study. For sorption studies, radioactive isotopes 141 Ce, 160 Tb, 169 Yb, 95 Zr, 181 Hf, and 95 Nb were prepared by neutron irradiation to trace the adsorption behaviors of their corresponding elements under certain conditions. Furthermore, radiochemical separation of the analyzed elements in the irradiated monazite samples in sulfuric acid solutions was carried out. Ion exchange technique was applied under static and dynamic conditions and the employed inorganic ion exchangers were locally synthesized and characterized using FT-IR and scanning electron microscopy (SEM) tools. Good group separation of the analyzed lanthanide elements from the accompanying elements was achieved.

The concentrations of 226 Ra, 232 Th, 40 K and 137 Cs radionuclides in soil samples collected from 323 different regions of Nevşehir province were determined by using a gamma spectrometer with an HPGe detector. The mean gamma activity concentrations (ranges) of 226 Ra, 232 Th, 40 K and 137 Cs for districts were determined as 49.45 (7.40–193.90), 54.08 (<2.8–122.50), 698.43 (37.67–1370.20) and 8.26 (0.10–52.60) Bq kg −1 , respectively. The mean activity concentrations of 226 Ra, 232 Th and 40 K were higher than the world mean value. According to Kolmogorov–Smirnov test, distributions of 226 Ra, 232 Th and 137 Cs show log-normal distributions. Whereas, 40 K shows normal distribution. The mean radium equivalent activity was 181.68 Bq kg −1 which is lower than the recommended maximum value of 370 Bq kg −1 . The mean external terrestrial gamma dose rate was found to be 85.12 nGy h −1 . The calculated external hazard value was 0.49 and within the acceptable limit which is less than unity (H ex  ≤ 1). Thermo Scientific RadEye NBR detector was used to determine environmental gamma dose rates. The gamma dose rates were measured at 445 points at a height of 1 m from land surface. The mean outdoor gamma dose rate (range) was found as 150.13 (50–480) nGy h −1 . This mean value was found higher than world mean value. The fact that most of the Nevşehir province is based on volcanic rocks explains why the gamma dose rates are high.