Purification of uranium product from plutonium contamination using acetohydroxamic acid (AHA) based process

Acetohydroxamic acid (AHA) based uranium product purification process to remove plutonium was optimized. For this process, equilibrium data was generated to optimize AHA concentration and acidity of stripping agent/scrubbing agent. Two options namely (i) Pu complexation in aqueous phase followed by extraction and scrubbing ii) extraction followed by scrubbing with AHA were studied. Results of these studies indicate that U product obtained in AHA purification is near to the table top specification and also quantitative Pu recovery from the AHA strip product is possible by oxalate precipitation.     

Sensitivity of Americium and Curium Splitting Flowsheet and Running Procedure

As part of the 2006 French Act on sustainable radioactive waste and waste management, CEA has been developing a process, (EXAm), in order to separate americium from curium and fission product downstream of COEXTM or PUREX processes. The goal is to recover Am up to 99%. The first step mainly consists of splitting americium from curium thanks to the diamide in organic phase combined with a complexing agent in high nitric acid. The low separation factor between Am and Cm leads to a very sensitive process flowsheet towards operating conditions. It is then difficult to manage high recovery yields with good purity. A model has been built taking into account complexation equilibria by TEDGA in aqueous phase and extraction equilibria in organic phase for each element. This model was put into the PAREX code to find the correct flowsheet, and then to conduct sensitivity studies regarding several parameters such as feed flow, acidity, temperature, solvent flow and reagent concentration. These studies have pointed out a high correlation between americium yield and decontamination factor and, also, an equivalence between any change of the most sensitive parameters and a change in TEDGA concentration. A running procedure was followed during two hot tests: the main concept was to start with a less efficient process and then to improve it during the test in order to reach required performances by adjusting the TEDGA flow rate.     

Extraction behaviour of uranium,zirconium and ruthenium with gamma-irradiated sulfoxides and tri-n-butyl phosphate

The extraction, scrubbing and stripping behaviour of uranium, zirconium and ruthenium with di-n-hexyl and di-n-octyl sulfoxides in Solvesso-100 and tri-n-butyl phosphate (TBP) in shell Sol-T irradiated by various gamma doses (0–169 Mrads) have been investigated. 2M HNO₃ was used for extraction and scrubbing and 0.01M HNO₃ for stripping purposes. Results indicate that the extraction of uranium with TBP increases and that with sulfoxide decreases with dose. This is reflected in their corresponding scrubbing percentages too. The stripping percentage of uranium with TBP decreases with dose while the reverse is the case with sulfoxide. The extraction of zirconium with TBP increases sharply with dose as compared to sulfoxides. The extraction scrubbing and stripping of ruthenium remain almost unaffected by dose both in the case of TBP and sulfoxides. These results lead to much higher overall decontamination factors for uranium with respect to zirconium as well as ruthenium with irradiated sulfoxides as compared to those with irradiated TBP.     

Purification and recovery of plutonium from uranium oxide obtained in the fast reactor fuel reprocessing plant using hydroxyurea as reductant

Spent fuel discharged from Fast Breeder Test Reactor (FBTR) in Kalpakkam is being reprocessed by modified plutonium uranium reduction extraction (PUREX) process using 30% TBP (tributylphosphate) as extractant in the presence of heavy normal paraffin (HNP) as diluent. Partitioning of uranium (U) and plutonium (Pu) is carried out using oxalate precipitation method. Uranium oxide product obtained by this method contains appreciable amount of plutonium which has to be recovered. Recovery of plutonium from this uranium oxide product is carried out by reducing Pu to inextractable Pu(III) using hydroxyurea (HU) and then uranium is extracted into 30% TBP. A small amount of Pu which is extracted in the organic phase is stripped back to aqueous phase by scrubbing with scrubbing agent containing 0.1 M HU in 4 M nitric acid. Similarly U and Pu are co-extracted into 30% TBP and then Pu is removed by scrubbing with 0.1 M HU in 4 M nitric acid. Further decontamination from Pu is obtained in the stripping stages. By this method Pu contamination in the uranium oxide is brought from 7300 ppm to 0.4–3 ppm (wt/wt). This uranium product obtained can be handled on table top.     

Hot Test in Mixer Settlers of Alpha Barrier with AHA in PUREX Process

In the PUREX process, the first U-Pu purification cycle (1CUPu) is not efficient enough for the decontamination of uranium flow out of neptunium. In this context, molecules known for their strong complexing power for actinides(IV) in aqueous phase, such as acetohydroxamic acid (AHA) have been tested in batch experiments to strip Np and Pu from TBP solvent loaded with U. A phenomenological model was developed and with the help of this model, a flowsheet of a counter-current alpha barrier process was designed and tested in C17 glove boxes in ATALANTE facility. A decontamination factor DFU/Np of 480 was obtained, higher than DFU/Np required by UNIREP standards.     

Hydrodynamics of the effectiveness of the AP-CITROX decontamination technology

During the optimization of the AP-CITROX decontamination technology the effect of the different flow rates of the decontamination solutions on the radioactive contamination and corrosion state of stainless steel tube samples originating from steam generators of Paks NPP were studied by a pilot-plant circulation system. The results have proved that a significant increase (up to 2.89 m/s) in the flow rate of the decontamination solution in the 1-5 steps is highly recommended and in order to improve the passivity of the surfaces it should be kept as low as possible (0.5 m/s) during the passivation.     

Microbiological decontamination of natural honey by irradiation

Degree of microbiological decontamination, organoleptic and physico-chemical properties of natural honeys were investigated after radiation treatment. Seven kinds of honeys were irradiated with the beams of 10 MeV electrons from a 10 kW linear accelerator “Elektronika 10-10” at the dose 10 kGy.

It was shown, that after irradiation, the total count of aerobic and anaerobic bacteria and moulds decrease by 99%. The antibiotic value in investigated honeys increased in turn from 1.67 to 2.67 after irradiation. Such factors and parameters of investigated honeys as their consistency, content of water and saccharose, acidity, the diastase and 5-HMF values were not changed significantly after irradiation.

Decontamination by irradiation is a process which allows us to obtain high microbiological purity of honeys. It is especially needed, when honeys are used in surgical treatment of injuries and in nutrition of babies with food deficiency.     

Solid formation behavior during the conditioning of simulated high level liquid waste for transuranic elements extraction

The acidity change and solid formation in a simulated high level liquid waste (HLLW) containing precipitate were experimentally examined, when the acidity was reduced from 2M to 0.5M by denitration or simple dilution. The acidity of the simulated HLLW containing precipitate could be adjusted from 2M to around 0.5M by means of denitration or dilution, as well as the case of simulated HLLW without precipitate. The precipitation fractions of Zr, Mo and Te during denitration decreased with increasing amount of the precipitate already contained in the simulated HLLW. The amount of solid formed in the dilute simulated HLLW also decreased with increasing amount of precipitate in the simulated HLLW. Two process flow sheets for preparing HLLW for transuranic elements extraction were developed. One was a denitration process and the other a dilution process.     

Effect of acidity and mesoporosity in H-USY on conversion of wheat straw to ethyl levulinate (Biofuel additive)

Cold flow properties of biodiesel can be improved by addition of additives especially ethyl levulinate (EL up to 20%). There are very limited information on synthesis of EL from actual raw biomass like wheat straw over heterogeneous catalyst. The present article elaborated on optimization of Acidity to Mesoporosity ratio in H-USY, which is crucial for its application in conversion of raw wheat straw to selective formation of EL in one-step. The acidity and mesoporosity is monitor by systematic post treatment of desilication and dealumination. Optimum acidity/mesoporosity ratio of 3.6 in HUSY resulted in to maximum EL yield of 24.5%, which is probably the highest so far.     

Nuclear waste treatment by means of supported liquid membranes containing calixcrown compounds

Permeability variation with repeated caesium transport experiments has been chosen to measure the leaching of the supported liquid membrane by the contacting aqueous solutions. This allowed us to characterize the SLM stability. Whereas classical crown ethers such as the widely used 21C7 derivatives were revealed to be poorly efficient and poorly stable in SLMs, crown-6-calix[4]arene compounds in the so-called1,3-alternate configuration led to very stable (over 50 days), highly selective (concentration factor>100) and efficient (decontamination factor=20) SLMs, for the removal of caesium from high salinity and acidity media. These results were achieved by using proper organic diluents and introducing hydrophobic substituents in the frame of the calixarenes.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Recent R&D towards Aqueous Reprocessing of FBR Fuels

The mixed Pu-rich carbide spent fuel with a burn up of 155 GWd/t from the Fast Breeder Test Reactor is being reprocessed in a hot-cell facility by PUREX process. Based on the input from the operation of this facility, R&D activities were carried out to improve the recovery, decontamination factors, economy and to reduce the waste volumes. Reduction of uranyl ions in a continuous flow electrochemical reactor and electrolytic as well as chemical reduction of 4M HNO₃ from liquid waste could be accomplished in continuous mode. Using the optimized parameters, suitable electrolytic cells/experimental setups were designed for the plant capacity of 6 L/h. Studies on the extraction kinetics of Ru with 30% TBP in NPH revealed that better decontamination factor with respect to Ru can be achieved using fast contactors like centrifugal extractors (CEs). Towards developing a spent solvent recovery system to reduce organic waste volumes, a pilot plant was set up, which could recover diluent as top product of distillation column and 40% TBP as bottom product from inactive degraded solvent. A solvent recovery system using short path distillation was also developed for installation in hot cells.     

Migration-plugging properties and plugging mechanism of microfoam

To gain a better understanding of the migration-plugging properties and plugging mechanism of microfoam, micromodel tests were conducted to investigate the factors controlling the bubble size and plugging mechanism of microfoam. The resistance factor, plugging ratio, and matching factor between average bubble diameter of microfoam and pore-throat diameter of core were introduced to characterize the migration-plugging properties of microfoam by core displacement experiments. The results showed that the average bubble diameter of microfoam could be tuned from 8.6 to 57.9?µm by changing the gas liquid ratio and the sandpack foam generator permeability. Microfoam showed both better injectivity and deep plugging capacity when the matching factor was 1.35–1.87 and the gas liquid ratio was 1:2–1:1. Microfoam would create a temporary blocking zone in the high permeable region through bubble accumulation, and the subsequent microfoam would flow through the low permeable region directly or by means of elastic deformation. With the increase of the gas liquid ratio, the flow pattern of the microfoam was changed from dispersed and isolated bubbles to dense and surface contact bubbles. The blocking mode of microfoam at the pore-throat was shown to shift from intermittent plugging to continuous plugging, leading to the enhancement of plugging capacity and deformability of microfoam.     

Solvent extraction of Sb(III) with malachite green into chloroform

A rapid and selective method for the solvent extraction of Sb(III) using malachite green (C. I. Basic green 4) has been described. Effect of different parameters affecting the extraction coefficient value of Sb(III) such as acidity, time of equilibration, KI concentration, solvents, anions, etc. has been studied. For various elements the separation factor has been evaluated. The stoichiometry of the extracted species has been determined by the method of substoichiometric extraction. The decontamination factor for some elements using substoichiometric quantities of the extracting agent has been evaluated. Radiotracers were employed for the extraction studies. The method elaborated has been employed for the quantitative determination of antimony in normal, benign and cancerous tissues of the human brain.     

Separation of Rare-Earth Elements from Nitrate Solutions by Solvent Extraction Using Mixtures of Methyltri-n-octylammonium Nitrate and Tri-n-butyl Phosphate

The article presents data on the solvent extraction separation of rare-earth elements (REEs), such as La(III), Ce(III), Pr(III), and Nd(III), using synergic mixtures of methyltrioctylammonium nitrate (TOMANO₃) with tri-n-butyl phosphate (TBP) from weakly acidic nitrate solutions. Specifically, experimental results on separation of REEs, for the pair Ce(III)/Pr(III) for quaternary mixtures of REEs (La(III), Ce(III), Pr(III), Nd(III)) and for the pair La(III)/Pr(III) for solutions containing La(III), Pr(III), and Nd(III), are presented. It was shown that effective separation for the pair Ce(III)/Pr(III) from a solution containing 219 g Ce(III)/L, 106 g La(III)/L, 20 g Pr(III)/L, 55 g Nd(III)/L, and 0.1 mol/L HNO₃, was achieved using 56 steps of a multistage, counter-current solvent extraction cascade with scrubbing, at an organic-to-aqueous phase volume ratio (O/A) equal to 2/1 on the extraction section and O/A equal to 4/1 on the scrubbing section, using 3.3 mol/L solutions of the mixture TOMANO₃-TBP with molar ratio 0.15:0.85 in dodecane. Separation for the pair La(III)/Pr(III) could be achieved using a solvent extraction cascade with scrubbing in 32 steps at O/A equal to 2/1 on the extraction section and O/A equal to 2.8/1 on the scrubbing section of the solvent extraction cascade from a solution containing 258 g La(III)/L, 58 g Pr(III)/L, 141 g Nd(III)/L, and 0.1 mol/L HNO₃ with 3.0 mol/L solution of the mixture TOMANO₃-TBP with molar ratio 0.2:0.8 in dodecane.     

Separation of Curium-Californium by Extraction Chromatography

Sequential separation of the trivalent actinides Cm and Cf is investigated by extraction chromatography using the system Alamine 336-LiCl on the diatomaceous earth, Celite 360. The effect of the mobile phase concentration and the acidity on the distribution behaviour of both elements is found almost to parallel that based on simple liquid-liquid extraction. Optimum resolution and efficient decontamination is readily achieved by 11 M LiCl in 0.02 M HC1. The possible use of the same system for the decontamination of the +3 actinides from various foreign ions is also pointed out.     

Separation of high purity gadolinium for reactor application by solvent extraction process

A solvent extraction process for the production of nuclear grade Gd₂O₃ for its applications in pressurized heavy water reactor (PHWR) from a crude concentrate of rare earths containing ~70 % Gd₂O₃ has been developed and tested on bench-scale and continuous counter-current operations. The separation of gadolinium from other rare earths with similar chemical properties has been successfully accomplished by adopting a dual cycle solvent extraction employing 2-ethylhexylphosphonic acid, mono-2 ethylhexyl ester (EHEHPA) as an extractant. Taking advantage of the extraction order of rare earths with EHEHPA, in the first cycle, heavy rare earths including Tb, Dy and Y were separated in the product strip solution, while gadolinium was separated in the raffinate solution along with samarium and neodymium. In the second cycle, gadolinium was purified to the extent of >99.5 % with respect to other rare earths. Effects of process variables such as aqueous acidity, phase ratio, metal concentration in the aqueous feed, scrubbing and stripping acidity etc. on separation of terbium and other heavy rare earths in the first cycle and upgrading the purity of Gd₂O₃ in the second cycle have been investigated. The experimental conditions were optimized using computer simulation and validated by bench scale counter-current operations. Under optimized conditions of process parameters, continuous operations of mixer settler yielded kilogram quantity of nuclear pure Gd₂O₃ which was subsequently converted to gadolinium nitrate for PHWR application. The overall recovery was found to be >98 %.     

Selective extraction of uranium from a mixture of metal or metal oxides by a tri-n-butylphosphate complex with HNO(3) and H(2)O in supercritical CO(2).

In order to study the decontamination nature of the reactive extraction of uranium in the presence of some metal chemicals using a single-phase mixture of HNO(3), H(2)O and tri-n-butylphosphate (TBP) in supercritical carbon dioxide (SC-CO(2)), we measured the decontamination factors (DFs) of Sr, Zr, Mo, Ru, Pd, Ce and Nd from their mixture with U. These elements were originally added to U(3)O(8) as SrO, ZrO(2), MoO(3), RuO(2), Pd, CeO(2) and Nd(2)O(3), and the extraction was performed at 18 MPa and 323 K with the single-phase mixture. The DFs for these elements were determined to be greater than 10(3) when the molecular ratio of U to TBP in the extracted complex was greater than 0.3. Dilution by SC-CO(2) effectively increased the DFs.     

Solvent extraction of Au(III) using 2-mercaptobenzimidazole into n-butanol

A method has been developed for the extraction of Au(III) with 2-mercaptobenzimidazole into n-butanol.¹⁹⁹Au has been used as a tracer for establishing the ideal extraction parameters such as effect of pH, time of equilibration, solvents and anions. Separation factor and decontamination factor have also been evaluated to determine the selectivity of the method with respect to various elements. The interfering elements were suppressed by the use of suitable masking agents which increased the selectivity. The stoichiometry of metal to reagent was determined by the method of substoichiometric extraction and slope ratio method.     

Separation of gram quantities of uranium from fission products by extraction chromatography

The separation of gram quantities of uranium from fission products has been investigated by extraction chromatography. The separation which is based on the difference in distribution coefficients between uranium and the fission products on a tributyl phosphate (TBP) resin in nitric acid medium, was carried out by means of high acidity feed and stepwise elution on a TBP chromatography column. The results show that this technique is capable to separate 5 g of uranium from a large quantity of fission products. The recovery of uranium is more than 99%. The decontamination factors of g- and b-activities were 2.1^.10³ and 2.3^.10³, respectively.     

Catalyst-Free Photochemical Activation of Peroxymonosulfate in Xanthene-Rich Systems for Fenton-Like Synergistic Decontamination: Efficacy of Proton Transfer Process

Catalyst-free visible light assisted Fenton-like catalysis offers opportunities to achieve the sustainable water decontamination, but the synergistic decontamination mechanisms are still unclear, especially the effect of proton transfer process (PTP). The conversion of peroxymonosulfate (PMS) in photosensitive dye-enriched system was detailed. The photo-electron transfer between excited dye and PMS triggered the efficient activation of PMS and enhanced the production of reactive species. Photochemistry behavior analysis and DFT calculations revealed that PTP was the crucial factor to determine the decontamination performance, leading to the transformation of dye molecules. The excitation process inducing activation of whole system was composed of low energy excitations, and the electrons and holes were almost contributed by LUMO and HOMO. This work provided new ideas for the design of catalyst-free sustainable system for efficient decontamination.