Modelling the reaction of uranium with carboxylic groups on surfaces through mono- and multi- dentate surface complexes on the basis of pH and redox potential

An analytical expression is proposed to simulate effects of pH and redox potential (E) on the sorption of uranium onto bioorganic model particles in saline or other aquatic environments. The elaborated expression is intended to avoid use of the classical approach of sorption which relies on experimental data and empirical models. The goal is to produce an expression that provides a distribution coefficient (Kd e.g. mL g-1) as function of pH, E and ligand concentration (through complex formation in solution) by applying a surface complexation model on one type of mono-dentate surface sites >(SuOH) as well as utilizing multi-dentate surface sites >(SuOH)c. The formulation of the worked out expression makes use of correlations between the surface complexation and hydrolysis constants for all species and sorption sites. The model was applied to the sorption of uranium onto bioorganic sites with and without carbonates in solution e.g. Log Kd: +2.75 at pH 8 for 2 sites per nm2. The calculated distribution coefficients were found very sensitive to the presence of carbonates, e.g. Log Kd: -7.0 at pH 8 for 2×10-3 M total carbonate. The potential reduction of uranium U(VI) and its complexes (carbonates) which are the primary stable species in surface waters, to U(IV) during sorption was simulated in association with a decrease in the redox potential and was found generally below the redox stability limits of water. The calculated distribution coefficient values were validated by the values reported in literature for the sorption of uranium onto specific adsorbents. The investigated simulations are also applicable to the sorption of other redox sensitive elements

Reaction of uranium with poly-hydroxy-aromatic groups on particles through mono- and multi-dentate surface complexes on the basis of pH and redox potential : A modelling approach

redox potential (E) on the sorption of uranium onto potentially redox active bioorganic model particles in saline or other aquatic environments. Specifically herein, it is applied to the mono- and poly-hydroxy-aromatic (polyphenolic) sites which account for approximately 30% of bioorganic site capacity. The derived expression is aimed to avoid use of the classical approach of sorption, which requires experimental data and empirical models. The expression provides a distribution coefficient (Kd e.g. mL g−1) as function of pH, E and soluble ligand concentration by considering a surface complexation model on mono- or multi-dentate complexation surface sites > Su(OH)c. The application of the model uses correlations between the surface complexation constants and hydrolysis constants, for all potential species and all form of sorption sites. The model was used to quantify the uranium sorption onto hydroxy-benzene, dihydroxy- enzene, and dihydroxy-naphthalene sites with or without carbonates in solution. The latter is the primary interfering reagent in waters that decreases Log Kd. The calculated distribution coefficients were found sensitive to both pH and E and very sensitive to the presence of carbonates. The reduction of uranium U(VI), and its carbonate complexes, to U(IV) during sorption was simulated by decreasing the redox potential. It was found that the transition phase between U(VI) and U(IV) was generally below the redox stability limits of water. However, the reduction of U(VI) to U(IV) was found to be potentially associated with their reaction with the polyphenols, decreasing the redox potential subsequently. The calculated sorption coefficient values were validated using the values reported in literature for the sorption of uranium onto specific adsorbents. The methodology of the simulation is also applicable to the sorption of other redox sensitive elements, and with the addition of a scaling factor, it would allow the predictions of co-complexation phenomena by employing relevant site formulations. The oxidation of mono-hydroxy- benzene in di-hydroxy-benzene enhances the sorption of uranium by a factor 106 which may be applied to its extraction from seawater

Short life fission products extracted from molten salt reactor fuel for radiopharmaceutical applications

This work studies the potential of using short life fission product ( AFp) radioisotopes e.g. 82Br, 86Rb, ( 90Sr) - 90mY, ( 99Mo) - 99mTc, 103Ru - 103mRh, 111Ag, 127Sb - 127(m)Te, 126I, 131I, 133Xe, 136Cs, 141Ce, 143Ce, 143Pr, 147Nd - 147Pm, 149Pm, 153Sm, 156Eu, 159Gd and 161Tb, extracted from a molten salt reactor and their separation using specific thermodynamic and radiochemical conditions. Their utilisation for coupled radiodiagnostics and radiotherapy is a key consideration. A molten salt reactor produces fission products during operation. These radioisotopes can be separated at line from the liquid fuel by evaporation/distillation, chemical reduction (using H 2 doped gas), electro-deposition and/or chemical oxidation (using Cl 2 doped gas). They can be refined and chemically treated for radiopharmaceutical use for imaging and radiodiagnostics utilising γ radioscopy or positron emission tomography, and potentially in radiotherapy to target specific cancers or viral diseases using β − emitters. Some of the AFp isotopes are currently used for radiodiagnostics because they emit γ rays of energy 50–200 keV. However, some may also be used in parallel for radiotherapy utilising their β − (E Mean ≈ 100 keV) emission whose mean free pathway of c.a. 100 nm in biological tissue is much smaller than their penetration depth. Focus is given to 86Rb, 90Y, 99mTc, 131I and 133Xe as well as on the ALn isotopes ( 141Ce, 143Ce - 143Pr, 147Nd - 147Pm, 149Pm and 153Sm) because of their strong potential for complexation with bio-ligands (e.g. DOTA) or for their ability to form micro-nano-spheres, and because of their potential for dual radiodiagnostics and radiotherapy. It is shown that these radio-lanthanides could also replace 177Lu for the treatment of specific cancers

Considerations for Prenatal Counselling of Patients with Cardiac Rhabdomyomas based on their Cardiac and Neurologic Outcomes

Cardiac rhabdomyomas are benign cardiac tumours with few cardiac complications, but with a known association to tuberous sclerosis that affects the neurologic outcome of the patients. We have analysed the long-term cardiac and neurological outcomes of patients with cardiac rhabdomyomas in order to allow comprehensive prenatal counselling, basing our findings on the records of all patients seen prenatally and postnatally with an echocardiographic diagnosis of cardiac rhabdomyoma encountered from August, 1982, to September, 2007. We analysed factors such as the number and the location of the tumours to establish their association with a diagnosis of tuberous sclerosis, predicting the cardiac and neurologic outcomes for the patients. Cardiac complications include arrhythmias, obstruction of the ventricular outflow tracts, and secondary cardiogenic shock. Arrhythmias were encountered most often during the neonatal period, with supraventricular tachycardia being the commonest rhythm disturbance identified. No specific dimension or location of the cardiac rhabdomyomas predicted the disturbances of rhythm. The importance of the diagnosis of tuberous sclerosis is exemplified by the neurodevelopmental complications, with four-fifths of the patients showing epilepsy, and two-thirds having delayed development. The presence of multiple cardiac tumours suggested a higher risk of being affected by tuberous sclerosis. The tumours generally regress after birth, and cardiac-related problems are rare after the perinatal period. Tuberous sclerosis and the associated neurodevelopmental complications dominate the clinical picture, and should form an important aspect of the prenatal counselling of parent

Mechanical Properties of Advanced Gas-Cooled Reactor Stainless Steel Cladding After Irradiation

The production of helium bubbles in advanced gas-cooled reactor (AGR) cladding could represent a significant hazard for both the mechanical stability and long-term storage of such materials. However, the high radioactivity of AGR cladding after operation presents a significant barrier to the scientific study of the mechanical properties of helium incorporation, said cladding typically being analyzed in industrial hot cells. An alternative non-active approach is to implant He2+ into unused AGR cladding material via an accelerator. Here, a feasibility study of such a process, using sequential implantations of helium in AGR cladding steel with decreasing energy is carried out to mimic the buildup of He (e.g., 50 appm) that would occur for in-reactor AGR clad in layers of the order of 10 lm in depth, is described. The implanted sample is subsequently analyzed by scanning electron microscopy, nanoindentation, atomic force and ultrasonic force microscopies. As expected, the irradiated zones were affected by implantation damage (<1 dpa). Nonetheless, such zones undergo only nanoscopic swelling and a small hardness increase (10%), with no appreciable decrease in fracture strength. Thus, for this fluence and applied conditions, the integrity of the steel cladding is retained despite He2+ implantation

The analysis of nuclear materials and their environments

Preface The nuclear materials and their environments require analyses before and during their utilization as well as after service during disposition not only from the current nuclear units but also from the planed or foreseen nuclear installations or systems in the future. Prior analysis, sampling, in a general sense, and sample treatment must be carried out when the analytical technique is not applied in situ, in a non invasive way, or in a in-line or on-line mode. The analysis may be carried out in situ, for example using a remote system, or in an underground laboratory in the considered phase. The analysis may also be done ex-situ with transfer of the sample and separation when needed. For all analyses, sample volume, mass or amount, the flux of reagent, the size of the analyzed part of the sample and the acquisition time or time of analysis are key parameters that may affect the detection limit. Information required such as the chemical or radioisotope activity, the mass or volume of the sampled and analyzed item, the concentration as fraction or molarity of dopants or contaminants and the type or size of structures in the studied phases have to be determined in a multi-scale approach at the nuclear scale, atomic or molecular scale, at the microscopic or macroscopic structural scale, at the bulk scale, at the component or system scale, and/or at the environmental or geographical scale according to the requirements of the study. Identification concerns the actinides, fission products or activated products as isotopes or elements, but also their speciation that may not only be done at the molecular scale but also in a broader sense such as at the environmental level. The time scale ranges from the femtosecond, accessible during a Free Electron Laser investigations to describe ultra-fast phenomena, through the nanosecond to the mega-second, then to the penta-second or giga-year scale: the time scale of uranium-238 half-life or of the age of the fossil natural geo-reactors. The explored energy range along the analytical methods goes also from the nano-eV (Mössbauer or nuclear magnetic resonance spectroscopy) to the giga-eV (muon-tomography) for example. Passive and active analytical methods have been revisited in this Work, with examples of their utilization in transmission, injection, diffusion or reflection modes. The sampling area, beam size and reagent quantities are either macroscopic, microscopic or nanoscopic in size, while spatial-temporal conditions makes excitation incidence vs detection directions possible through solid angles, with synchronous detection or with temporal delay. In this Work the investigated analytical techniques have been classified according to their interactions, if any, between incident waves, particles or injected reagents and the analyzed sample, and, for their detected or recorded signals. For passive techniques, excitations are absent and phonons, photons, leptons, neutrons or ions are detected or quantified for their energy, flux, activity, quantity or mass. For interactive techniques, irradiations or reagent additions are made with phonons, photons, leptons, neutrons or ions with a known energy, flux, activity or mass. The irradiation or injection is done locally while the reception may be carried out in a given space at a given angle from the stimuli direction or the incident beam, instantaneously or after a certain delay after irradiation. The detection tools are spectroscopy, microscopy or radiography or tomography. The reaction takes place within or without a specific field such as electrical, magnetic, flow or mechanical acceleration. The detected signal may be the same in nature as the incident one, with the same energy, elastic interaction, or a signal with lower energy and inelastic interaction, with particles being again phonons, photons, leptons, neutrons or ions. In addition to these analytical tools or techniques, neutral species such as atoms or molecules may also be used to interrogate the material. They are treated as ions from a mass and charge point of view. The techniques are classified according to increasing energy of reagents or incident particles or waves. The combination of all excitation or reagent addition, and product detections makes the analytic potential very rich to perform the identification of molecules, elements or isotopes, their quantitative determination, and their spatial speciation. There has been an optimization of techniques and the discovery of new analytical tools over the last century or decades. Some of the techniques are found today obsolete, other reemerge due to new interests; some may be completed by combining the potential of one technique with another. In addition, there has been a constant challenge in pushing the use of the analytical techniques toward lower detection limits, better lateral and depth resolutions, more extreme applications and more flexible uses. As far as the nuclear materials are concerned, studies must reflect the demanding conditions of temperature, pressure and irradiation under which they are used. These materials act as barriers and their properties are investigated with emphasis on mechanical performances, durability, plasticity and stability when damaged or loaded by dopants or contaminants. These materials range from fuels for thermal or fast reactors, to structural materials. Fuels are analyzed prior and after irradiation, after their reprocessing for recycling and later as waste forms. Macro-properties such as thermodynamic, thermophysical and mechanical as well as microstructural analysis of these materials have to be analysed for example comparing again properties prior and after irradiation. As far as the environments of nuclear materials are concerned, one has to think the way the analyst and the environmental scientist would collaborate together to produce data that can be used by modelers or by authorities. The challenge is however to understand the behavior of actinide elements, fission products and other contaminants in the environment. Biogeochemical pathways have to be described, quantified and understood. Transport of actinides, fission products and other contaminants in fluids such as air or water includes particulate or colloidal phases. These analyses must be integrated in the analytical strategy as specific species for modeling their biogeochemical behavior. Data are provided by the analysts for the scientists and the modellers. The problem is to understand the behaviour of radionuclides in the systems or the material properties with regard to its integrity. In the environment, contaminant pathways have to be described. The contaminated systems interact with the local environment that may modify radionuclide speciation by physical-chemical processes. The analytical results must be integrated in the study for modelling their chemical and physical properties. A challenge for future investigations will be to find and develop direct analytical probes for full nuclear material characterisation at very low defect, dopant or contaminant concentrations to better characterize the damages, species or structures and to predict their behaviour in homogeneous, heterogeneous or complex nuclear materials and in their environments. Claude Degueldr

Uranium as a renewable for nuclear energy

Uranium extraction is the first step of the nuclear fuel cycle. Currently, uranium is only extracted from solid ores such as uranium rich minerals (% level) or minerals such as phosphates (ppm level). For some years extraction of uranium from sea water (ppb level) has been the topic of investigations particularly in Japan due to its national interest. In the huge oceanic volume the amount of uranium is constant, regulated by its river input (soluble) and balanced by its scavenging (particulate) on the sea floor. This work shows that the uranium extraction with parsimony from sea water could be carried in a renewable way if its concentration remains quasi constant. Recommendations for the extraction with use of gel panels or with braid of fabric grafted by sorbing groups in high tide or oceanic pelagic current environments are suggested along with a reduction of the uranium consumption

Uranium trioxide behavior during electron energy loss spectroscopy analysis

A sample of uranium trioxide (UO3) was produced by focused ion beam (~10 μm×~10 μm×<0.5 μm) for transmission electron and electron energy loss (EEL) spectroscopy examinations in a transmission electron microscope (TEM). The EEL spectra were recorded as a function of the thickness for the P and O edges in the low energy range 0–350 eV and were compared to spectra of UO3 small grains attached to a TEM grid. The EEL spectrum was studied through a range of thicknesses going from ~60 to ~260 nm. The EEL spectra recorded for UO3 are compared with those recorded for UO2. The reduction of UO3 into U4O9 and/or UO2 is readily observed apparently during the TEM investigations and as confirmed by electron diffraction (eD). This redox effect is similar to that known for other redox sensitive oxides. Recommendations are suggested to avoid sample decomposition