Coated UN microspheres embedded in UO2 matrix as an innovative advanced technology fuel: Early progress

• Uranium nitride (UN)-uranium dioxide (UO2) composites have been proposed as an innovative advanced technology fuel (ATF) option for light water reactors (LWRs). However, the interdiffusion of oxygen and nitrogen during fabrication result in the formation of α-U2N3. A way to avoid this interaction is to coat the UN with a material that is impermeable to oxygen and nitrogen, has a high melting point, high thermal conductivity, and reasonable low neutron cross-section. Among many candidates,refractory metals may be the first option. In this study, we present an early progressresult of fabricating an innovative ATF concept: coated UN microspheres embedded in UO2 matrix. To do so, the following steps are performed: 1) diffusion couple experiments of UN-X-UO2 (X=W, Mo, Ta, Nb, V) to evaluate the interactions between the coating candidates (X) and the fuels; 2) selection of the most promising candidates; 3) use a surrogate material (ZrN microspheres) to develop processes to coat the microspheres with nanopowders: dry and wet methods; 4) coating the UN microspheres with a selected method; 5) finally, sinter a coated UN-UO2 composite using spark plasma sintering (SPS), and compare the results with an uncoated UNUO2 composite sintered at the same SPS conditions (1500 °C, 80 MPa, 3 min,vacuum). The diffusion couple results indicate W and Mo as the most promising candidates, with the wet method showing the smoothest surface. So, dense (~95 %TD) W/UN-UO2 and Mo/UN-UO2 were sintered and the preliminary results show that the tungsten coating was not efficient due to poor adhesion. Conversely, the Mo coating (~15 µm) was efficient against the α-U2N3 formation. Therefore, this early progress indicates the possibility of fabricating an innovative ATF concept using a low cost and potentially applicable coating method.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Kompositmaterial och -teknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Composite Science and Engineering (hsv//eng)

Nyckelord

Composite UN-UO2

UN microsphere

accident tolerant fuel

coating technology

Kärnenergiteknik

Nuclear Engineering

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