ADONIS MARCELO SALIBA SILVA

ADONIS MARCELO SALIBA SILVA

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Nickel electrodeposition in LEU metal foil annular targets to produce Mo-99
2022 - IANELLI, RICARDO F.; SALIBA-SILVA, ADONIS M.; TAKARA, ERIKI M.; GARCIA NETO, JOSE; SOUZA, JOSE A.B.; CARVALHO, ELITA F.U. de; DURAZZO, MICHELANGELO
The most used production route of Mo-99 is through the fission of U-235 in irradiation targets that are irradiated in research reactors. The annular target is a promisor design since it can incorporate high U-235 quantities, thus increasing the production yield of Mo-99. This target type uses a foil of uranium metal enveloped by a thin nickel foil that acts as a diffusion barrier. The process of uranium enveloping with nickel foil is today done manually. This operation risks the nickel foil breaking up during target assembling. In the present work, we studied the nickel electrodeposition over uranium metal foil surfaces to replace nickel foils. A pre-forming procedure of the uranium metal foil by calendering was developed to facilitate the assembling operation. The electrodeposition was done over the uranium foil pre-conformed in a tubular shape. An automated apparatus for electrodeposition of nickel in uranium tubular-shaped foil was developed. The results showed that the high nickel adherence to uranium metal depends on the proper activation of the uranium surface. Among the activation processes studied, the mechanical activation showed good adhesion of the nickel layer, with a loss of only 0.16% of uranium mass. Homogeneous and regular 12 μm thickness electrodeposited layers over the uranium metal were obtained. This work showed that the process could be used in continuous production technology, such as the production of irradiation targets.
The comparison of the corrosion resistance of advanced ferritic stainless steels by Mott-Schottky approach
2009 - MARQUES, R.A.; TERADA, M.; SALIBA-SILVA, A.M.; PADILHA, A.F.; COSTA, I.
Ferromagnetic stainless steels (SS) have been investigated as potential candidates for dental prosthesis applications in replacement of magnetic attachments made of noble and expensive alloys. In order to be used as biomaterials, their corrosion resistance has to be appropriate. The corrosion resistance of passive materials is related to the characteristics of the passive film formed and this property might be investigated by Mott-Schottky procedure. The capacitance of passive films formed during 2 days of immersion in a Phosphate Buffered Solution (PBS), at room temperature on PM2000, DIN 1.4575 and 17-4 PH ferritic stainless steels (SS) was studied by Mott-Schottky approach. A commercial alloy was also analyzed for comparison reasons. The results showed that films on tested materials behave as both, n-type and p-type semiconductors and the PM2000 presented the highest corrosion resistance among all materials studied.
Manufacturing LEU-foil annular target in Brazil
2022 - DURAZZO, MICHELANGELO; SOUZA, JOSE A.B.; IANELLI, RICARDO F.; TAKARA, ERIKI M.; GARCIA NETO, JOSE S.; SALIBA-SILVA, ADONIS M.; CARVALHO, ELITA F.U. de
Molybdenum-99 is the most important isotope because its daughter isotope, technetium-99m, has been the most used medical radioisotope. The primary method used to produce Mo-99 derives from the fission of U-235 incorporated in so-called irradiation targets. Two routes are being developed to make Mo-99 by fissioning with low enriched uranium (LEU) fuel. The first adopts UAlx-Al dispersion plate targets. The second uses uranium metal foil annular targets. The significant advantage of uranium foil targets over UAlx-Al dispersion targets is the high density of uranium metal. This work presents the experience obtained in the development of the uranium metal annular target manufacturing steps. An innovative method to improve the procedure for assembling the uranium foil on the tubular target was presented. The experience attained will help the future production of Mo-99 in Brazil through the target irradiation in the Brazilian Multipurpose Reactor (RMB).
Kinects and factors on chemical dissolution of aluminum alloy AA6061 in NaOH alkaline media
2020 - TAKARA, E.M.; SOUZA, J.B. de; CARVALHO, E.F.U.; SILVA, A.S.
Nuclear Medicine is the Field of science that uses radioactive materials in order to diagnose and treat human body deceases. One of the most used radioisotopes for images diagnose purpose is the metastable technetium-99 (99mTc) because of its low decay half life (6 hours) and energy emission of 140keV that ensures low exposition time with the capacity of generating high quality images. The 99mTc is generated by the molibdenum-99(99Mo) radioactive decay during about 66 hours. The 99Mo is fabricated via nuclear fission of low encriched uranium (LEU) through plate irradiation targets (UAlx). The irradiation target cladding is made of Aluminum alloy AA6061 and its substrate is composed by 235U powder scattered in an AA1050 matrix. In general, studies are made targeting the prevention of corrosion mechanisms but the chemical dissolution in alkaline media, under hot cells, are one of the steps required for the post-processing methods of irradiation targets The time spent after irradiation is an important factor because the half life radioactive decay of the produced radioisotopes is relative short, then the procedures of dissolution, extraction, purify and distribution must be optimized in order to increase efficiency. This work presents a study of the factors impact involved on the chemical dissolution of the cladding aluminum alloys (temperature, NaOH solution concentration and dissolution time) as well as the kinects of the process associating it with the formation and destruction of oxides using electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). It was found that the involved parameters contribute individually more effective and that there is no relevant association between the factors. Solution temperature showed to be the most influent factor following by exposition time. It was presented a equivalent circuit model which demonstrates the reaction kinects and the growing of passive layers that slow down the process before it turns up into a soluble phase.
Quantification of crystalline phases of uranium silicide using the Rietveld method
2018 - GARCIA, RAFAEL H.L.; SALIBA-SILVA, ADONIS M.; LIMA, NELSON B. de
Uranium silicide is a material widely used as nuclear fuel for MTR (Material Testing Reactor), due to its performance in reactor environment. Some of its characteristics make it also attractive for its use in power reactors. However, each crystalline phase of uranium silicide have different behavior under irradiation. In this sense, it is important to perform crystalline phase characterizations, which are commonly obtained in the fabrication process. For this purpose, in this work U-Si alloys containing 33, 40, 41, 42, 50 and 67 mol% of silicon were molten in an induction furnace. Quantification of formed crystalline phases was carried out by Rietveld refinement of X-ray diffraction data. Calculated densities were compared to measured data from helium pycnometry.
Manufacturing low enriched uranium metal by magnesiothermic reduction of UF4
2018 - DURAZZO, M.; SALIBA-SILVA, A.M.; MARTINS, I.C.; CARVALHO, E.F.U. de; RIELLA, H.G.
This work presents an experimental description of thermal and physical studies to attain a practical manufacturing process of uranium metal enriched to 20% U235 (LEU–Low Enriched Uranium) by metallothermic reduction of UF4, with nuclear purity, for reduced amounts (1000g of uranium). The magnesiothermic reduction is influenced by the thermal conditions for UF4 reduction. These variables are investigated. The physical arrangement of the crucible/reduction reactor/furnace system and the management of the furnace thermal input in the reduction reactor during the heating were studied. Thermal simulation experiments provided delineation for the reactants’ thermal progress before the ignition of the reaction. The heat input to the reduction system has proved to be the main variable that influenced the efficiency of the process. The levels of metallic yield and reproducibility have been improved. The typical yield in the production of uranium metal was above 80%.
Analysis of slag formation during UF4 magnesiothermic reduction
2017 - DURAZZO, MICHELANGELO; SALIBA-SILVA, ADONIS M.; GARCIA, RAFAEL H.L.; CARVALHO, ELITA F.U. de; RIELLA, HUMBERTO G.
Metallic uranium is a fundamental raw material for producing nuclear fuel elements for research reactors and irradiation targets for producing 99Mo, as U3Si2, UMo alloy, UAlx, and uranium thin foils. Magnesiothermic reduction of UF4 is a possible route in the nuclear fuel cycle for producing uranium as a metal ingot. The main concern about the reducing scale to produce low-enriched (metallic) uranium (LEU) (around 1 kg) is the relatively low yield compared to calciothermic reduction. Nevertheless, the magnesiothermic reduction has the advantages of having lower cost and being a safer method for dealing with uranium processing. The magnesiothermic process, as a batch, is closed inside a sealed crucible. In the present study, in order to have a qualitative idea of the kinetics during the ignition moment, the slag projected over the lateral inner face of the crucible was used to sketch the general magnesiothermic evolution. The methods used were metallographic observation and X-ray diffraction followed by Rietveld refinement. The results of these analyses led to the conception of a general reaction development during the short time between the ignition of the reducing reaction and final settlement of the products. Relevant information from this study led to the conclusion that uranium is not primarily present in the lateral slag projection over the crucible during the reaction, and the temperature level may reach 1500°C or more, after the ignition.
Production of uranium tetrafluoride from the effluent generated in the reconversion via ammonium uranyl carbonate
2017 - SILVA NETO, JOAO B.; CARVALHO, ELITA F.U. de; GARCIA, RAFAEL H.L.; SALIBA-SILVA, ADONIS M.; RIELLA, HUMBERTO G.; DURAZZO, MICHELANGELO
Uranium tetrafluoride (UF4) is the most used nuclear material for producing metallic uranium by reduction with Ca or Mg. Metallic uranium is a raw material for the manufacture of uranium silicide, U3Si2, which is the most suitable uranium compound for use as nuclear fuel for research reactors. By contrast, ammonium uranyl carbonate is a traditional uranium compound used for manufacturing uranium dioxide UO2 fuel for nuclear power reactors or U3O8-Al dispersion fuel for nuclear research reactors. This work describes a procedure for recovering uranium and ammonium fluoride (NH4F) from a liquid residue generated during the production routine of ammonium uranyl carbonate, ending with UF4 as a final product. The residue, consisting of a solution containing high concentrations of ammonium (NH4 þ), fluoride (F ), and carbonate (CO3 2 ), has significant concentrations of uranium as UO2 2þ. From this residue, the proposed procedure consists of precipitating ammonium peroxide fluorouranate (APOFU) and NH4F, while recovering the major part of uranium. Further, the remaining solution is concentrated by heating, and ammonium bifluoride (NH4HF2) is precipitated. As a final step, NH4HF2 is added to UO2, inducing fluoridation and decomposition, resulting in UF4 with adequate properties for metallic uranium manufacture.
Sintered Nickel Casing for Irradiation Targets
2016 - MIYANO, R.S.L.; TAKIISHI, H.; SOARES, E.P.; SALIBA-SILVA, A.M.; ROSSI, J.L.
The aim of this work was to develop an alternative way to obtain casings used with irradiation targets containing uranium, for the production of the radionuclide Mo-99-Tc99m. The targets used for the production of Mo-99 are materials containing U-235 designed to be irradiated in a nuclear reactor. Usually these targets are encapsulated in aluminum or stainless steel. The idea here is to obtain casings by encapsulating a uranium button or a metallic cylinder with compacted and sintered nickel powder, this serving as a sealing for the fissile products occurring during U-235 irradiation. The sintered high purity nickel powder samples were compacted in uniaxial hydraulic press at 195 MPa. The sintering of the samples was carried out in an open-air furnace in an atmosphere with a certain control using titanium-machining chips at 600 ˚C. The samples bulk density was evaluated by the Archimedes' principle. The porosity of 20.08% was measured by mercury porosimetry. The microstructure was investigated by scanning microscopy revealing interconnected porosity and nickel oxide at the particles boundary surface. The results obtained by sintering of nickel powder according to the experimental undertaken, indicate the feasibility of achieving a casing for uranium targets.
Structural and microstructural characterization of U3Si2 nuclear fuel using X-ray diffraction
2017 - ICHIKAWA, RODRIGO U.; GARCIA, RAFAEL H.L.; SILVA, ANDRE S.B. da; TURRILLAS, XAVIER; SALIBA-SILVA, ADONIS M.; LIMA, NELSON B.; MARTINEZ, LUIS G.
In this work, two uranium silicide powdered samples, containing 67% and 42 mol% of Si, were analyzed using X-ray diffraction (named as 67Si and 42Si). For structural characterization, Rietveld refinement was used to estimate cell parameters, volume fraction (weight percent) of crystalline phases and atomic positions. For the main phases, X-ray line profile analysis (XLPA) was used to estimate mean crystallite sizes and microstrains. The 67Si sample presents higher content of USi2 (tetragonal) and the 42Si sample presents higher content of U3Si2 (tetragonal) as identified and calculated from the XRD profiles. Overall there are no appreciable structural changes and the parameters refined are in good accordance with the ones reported in the literature. Mean crystallite sizes determined by XLPA revealed small crystallites of the order of 101 nm and low microstrain for all samples.