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Theses

Conversion des nitrates d'actinides en oxydes par combustion en solution

Abstract : Research projects have started in the purpose to improve the processes involved in the treatment and recycling of spent nuclear fuel for the IV generation nuclear reactors SFR. Usually, the obtained actinides after the treatment of spent nuclear fuel are in the form of nitrates or in nitric acid solution. Currently the processes are based on thermal decomposition allowing to obtain actinides oxides like UO2 or (U,Pu)O2. Moreover, the powders as prepared needs thermal and mechanical treatment in order to be use for the sintering of nuclear fuel pellets. Therefore, the conversion process must be improve and the Solution Combustion Synthesis (SCS) method was adopt for the nitrate to oxide conversion and it appears to be interesting for the treatment and recycling of spent nuclear fuel.This thesis has focused on two main objectives: To understand the SCS reaction’s mechanisms and to optimize the various parameters in order to obtain the uranium oxides and mixed oxides with improved properties. In this purpose, we studied the conversion of actinides nitrates to oxides by SCS using gadolinium nitrate as a simulant of actinides, and investigated the effects of parameters like the chemical properties of chosen organic fuel, the heating rate and mixture’s fuel richness. These investigations showed the possibility to study the uranyl nitrate into oxide conversion by SCS with optimal parameters. We effectively applied with optimized parameters for the direct conversion of uranyl nitrate into an UO2 (oxide), where uranium reduction mechanisms depends on chosen organic fuel. These results have used to study the co-conversion of a uranyl nitrate and cerium nitrate mixture into a mixed oxide, which changes from industrial process. Finally, the sintering of uranium oxide and mixed uranium-cerium oxide pellets have studied to conclude about the possibility of a final process using SCS.
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Submitted on : Monday, October 12, 2020 - 4:07:09 PM
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Julien Monnier. Conversion des nitrates d'actinides en oxydes par combustion en solution. Autre. Université Montpellier, 2019. Français. ⟨NNT : 2019MONTS091⟩. ⟨tel-02964683⟩

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