NATHANAEL WAGNER SALES MORAIS
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Artigo IPEN-doc 30363 Thermal fatigue of Zircaloy‑4 cladded U‑7.5Nb‑2.5Zr2024 - MORAIS, NATHANAEL W.S.; MONLEVADE, EDUARDO F.; SCHON, CLAUDIO G.Prototype plates made of U-7.5Nb-2.5Zr alloy, also known as Mulberry alloy, cladded with Zircaloy-4 were thermally fatigued between 200 ºC and 500 ºC investigated. The assembly consisting of a Uranium alloy monolithic core and the Zircaloy-4 cladding was processed by hot rolling and investigated in the “as rolled” state, as well as after applying 9% and 18% reduction in cold rolling. The samples were characterized by Optical microscopy and X-Ray diffraction both before and after the thermal cycling. All samples presented strong volume contraction (shrinkage) in the first thermal cycle, observed concomitantly with the γ → α" transformation. The relative shrinkage varied with the cold rolling level, being larger for the “as rolled” plate. The failure mechanism observed in all plates was fracture alongside the U-alloy/Zircaloy-4 interface and no transverse crack was observed either in the Zircaloy-4 sheet or in the Uranium core.Artigo IPEN-doc 29909 Microstructural characterization of U-7.5Nb-2.5Zr alloy after ageing and constrained fatigue2023 - MORAIS, NATHANAEL W.S.; MUCSI, CRISTIANO S.; FABRIM, ZACARIAS E.; SCHON, CLAUDIO G.; ROSSI, JESUALDO L.U-7.5Nb-2.5Zr cladded in Zircaloy-4 is one of the most studied fuel prototypes. The Nb and Zrare added to the U to stabilize the body-centered cubic (BCC) gamma phase and grant mechanical and swelling resistance. The U-7.5Nb-2.5Zr undergoes the gamma to α′′ phase transformation, generating compressive stresses due to the volume reduction. The α′′ phase also can transform to a combination of α + γ2 phase (equilibrium phases), which are known to be hard and brittle. This work had the objective to test the effect of ageing the gamma to α′′ phase in thermal cycling of a U-7.5Nb-2.5Zr cladded in Zircaloy-4 part. A co-laminated specimen was aged and thermally cycled in a dilatometry experiment. The samples were characterized through X-ray diffraction and metallography. The results show that the gamma to α′′ phase transformations occur at the begin- ning of the initial ageing, followed by stress relief. During the cycling, the sample demonstrated non-equal thermal strains and presented fractures along with the U matrix.Artigo IPEN-doc 29897 Surface contaminants’ incorporation after nanosecond laser ablation2023 - STIPP, WAGNER; MORAIS, NATHANAEL W.S.; MARTINS, JOSÉ V.; MATOS, PRISCILA; ROSSI, JESUALDO L.; ROSSI, WAGNER de; RAELLE, MARCUS P.Decontamination and cleaning of surface-contaminated radioactive waste using laser ablation is a promising new technique being researched. One advantage is the potential to recycle waste and reduce the demand for repository storage. However, prior studies have shown that residual radioactivity can persist after laser decontamination indicating the incorporation of contaminants beneath the surface of metal samples. In this study, a q-switched laser was used to measure the depth of the recast zone at various fluences and simulate a decontamination process using a gold-coated sample. The results showed that surface material was found in the recast zone for fluences ranging from 1 to 10 J/cm2. This suggests that incorporation of surface contaminants after laser ablation is an important issue that must be considered before using this technique for radioactive waste treatment.Artigo IPEN-doc 27721 Crystallographic texture of hot rolled uranium-molybdenum alloys2020 - NIELSEN, G.F.; MORAIS, N.W.S.; LIMA, N.B.The uranium molybdenum (U-Mo) alloys have the potential to be used as low enriched uranium nuclear fuel in research, test, and power nuclear reactors. U-Mo alloy with composition between 7 and 10 wt% molybdenum shows excellent body centered cubic phase (γ phase) stabilization and presents a good nuclear fuel testing performance. Hot rolling is commonly utilized to produce nuclear fuel plate where it promotes the cladding and the fuel alloy bonding. The mechanical deformation generates crystallographic preferential orientation, the texture, which influences the material properties. This work studied the texture evolution in hot rolled U-Mo alloys. The U7.4Mo and U9.5Mo alloys were melted in a vacuum induction furnace, homogenized at 1000°C for 5 h, and then hot rolled at 650°C in three height reductions: 50, 65 and 80%. The crystalline phases and the texture were evaluated by X-ray diffraction (XRD). The as-cast and processed alloys microstructures were characterized by optical and electronic microscopies. The as-cast, homogenized, and deformed alloys have the γ phase. It was found microstructural differences between the U7.4Mo and U9.5Mo alloys. The homogenized treatment showed effective for microsegregation reduction and was not observed substantial grain size increasing. The deformed uranium molybdenum alloys presented α, γ, θ texture fibers. The intensity of these texture fibers changes with rolling reduction.