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Réalisation de joint de scellement céramique par projection plasma et caractérisation thermomécanique

Abstract : This project was supported by Andra under the "Investments for the Future Programme" ("Investissement d'Avenir") organized in cooperation with the French National Research Agency (ANR). The aim of this study, was to seal an aluminosilicate overcontainer that will contain a primary container with radioactive waste through means of plasma spray. Before this project the composition of the ceramic container has been optimized with 72 % in mass of alumina to produce a demonstrator (half size (Height 60 cm Diameter 33 cm) excepted for the thickness of the wall (4 cm)), referenced P72. Unfortunately, at the beginning of this project, major defect inside the sintered part has led to the impossibility to proceed to the welding. Another composition was selected, easier to cast but with lower mechanical properties with 50 % in mass of alumina, referenced B50. Firstly, the effect of the heating by plasma torch of the ceramic massive simulating the overcontainer P72 (72% in mass of alumina) is envisaged. At the same time 4 alumina-based thick coatings, with shape close to weld join, were obtained by plasma spray as possible candidates for sealing material. These coatings are as follows: aluminosilicate PP48 (48% in mass of alumina), PP72 (72% in mass of alumina) alumina-sodalime glass PPAV (85% in mass of alumina) and alumina-titania PPAT (87% in mass of alumina). The chemical compositions (by XRD and XRF) and microstructures (SEM, porosity by Archimede's principle and helium pycnometry) of two aluminosilicate sintered bodies B50 (50% in mass of alumina) and P72 (72% in mass of alumina) as well as of the coatings were investigated. Both the massive pieces and the coatings were further characterized thermomechanically. Under load at room temperature, 4-points bending test coupled with acoustic emission monitoring were conducted to well understand and interpret the microstructural changes occurring during loading. At high temperature, dilatometric, ultrasonic echography and acoustic emission measurements were carried out, to characterize and understand deeper the microstructural evolutions of materials subjected to thermal stresses. These analyses were performed on both the sintered samples and the coatings in order to determine the compatibility between them and to possibly predict their behavior during the sealing procedure and under mechanical load. P72 outperformed B50 in mechanical properties as the latter presented intrinsic cracks caused by the quartz transition at 573°C. At the same time PPAT coating presented the highest mechanical strength of all the coatings; however, the intrinsic cracks caused by the anisotropic thermal expansion of aluminum titanite reduced its potential as a possible candidate for a sealing material.
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Submitted on : Tuesday, September 27, 2022 - 3:21:56 PM
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Victor Badea. Réalisation de joint de scellement céramique par projection plasma et caractérisation thermomécanique. Matériaux. Université de Limoges, 2022. Français. ⟨NNT : 2022LIMO0065⟩. ⟨tel-03789597⟩

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