Experimental Investigation of MOX Fuel Processing for LFR-SMR Applications

Small Modular Reactors are gaining global traction as a transformative solution for clean, reliable, and scalable nuclear energy. They offer several advantages over traditional large-scale nuclear plants: reduced capital costs, faster deployment, enhanced safety features, and modular factory-based construction. SMRs are also being considered for diverse applications such as district heating, hydrogen production, and off-grid electrification, making them a cornerstone of future energy strategies. Among the various SMR technologies, Lead-cooled Fast Reactors (LFRs) represent a promising Generation IV design. These reactors use liquid lead as a coolant, offering high thermal conductivity, chemical inertness, and passive safety features. The European EAGLES-300 initiative, led by a consortium including the Belgian Nuclear research Centre SCK CEN and the Italian National Agency for New Technologies, Energy and Sustainable Economic Development ENEA, aims to commercialize a 350 MWe lead-cooled SMR by 2039. This design supports industrial heat applications and hydrogen production, while utilizing MOX (Mixed-Oxide) fuel containing up to 30 wt.% Pu/[U+Pu] content, to compensate for the reduced core size and maintain reactor performance.

The Fuel Materials (FMA) expert group performs research projects in the domain of nuclear fuel production and characterization, covering the front-end fuel fabrication processes from aqueous feeds to powders and sintered fuel pellets, rodlet loading & welding. The FMA group operates and maintains two laboratories, which feature all infrastructure and tools relevant for conventional powder metallurgical processes and liquid-to-solid conversion processes e.g. mixing and milling devices, pressing tools, furnaces, analytical equipment at laboratory-scale, either in fume hood environment for uranium, thorium and surrogate studies, and in glove-box environment for materials containing transuranic elements.

To gain a comprehensive understanding of high Pu-content MOX fuel manufacturing, it is essential to investigate the powder properties of PuO₂ and UO₂ feed materials, and their effect on the different manufacturing process steps. However, direct experimentation with PuO₂ involves significant material consumption and radiological constraints. Therefore, this Master Thesis will employ CeO₂ as a surrogate for PuO₂, enabling systematic exploration of key fabrication parameters. The study will focus on various aspects of the process, including blending and milling techniques, characterization of feed and blended powders, and thermal treatment conditions during calcination and sintering. A range in CeO₂ concentrations will be selected to simulate MOX fuel with different Pu-enrichment. Solid-state characterization will involve optical and electron microscopy, particle size and surface area analysis, density measurements, and X-ray diffraction. Furthermore, in-situ techniques such as thermogravimetric analysis and dilatometry, complemented by microstructural examination using electron probe microanalysis are available.