Design rules for industrial-scale sintering of UB4-UBC composites with high uranium density

Abstract

Uranium borides are promising candidate fuel forms for use in advanced nuclear reactors due to their high thermal conductivity and potential for dual use as both fuel and burnable absorber materials. In this work, uranium tetraboride (UB$_4$) and uranium monoboroncarbide (UBC) composites were synthesized using an industrially scalable borocarbothermic reduction method. The high-temperature structural evolution of the as-synthesized borides was investigated using in situ synchrotron X-ray diffraction (SXRD). The oxidation behavior was further characterized using a combination of SXRD and thermogravimetric analysis (TGA), allowing direct comparison with other potential accident-tolerant fuels such as UB$_2$, U$_3$Si$_2$, UC, and UN. The UB$_4$-UBC composite shows higher uranium loading than monolithic UB$_4$ and demonstrates promising oxidation behavior at elevated temperature, pointing to its potential as an improved uranium boride-based fuel form.

Figures (9)

• Figure 1: (a) Heating profile for synchrotron characterization of a UB4 and UB4–UBC composite sample (b) Double layer containment sketch for UB4–UBC sample in quartz capillaries (c) High temperature in situ heating XRD setup at 28-ID at NSLS II.
• Figure 2: Temperature dependence of the Gibbs free energy of formation ($\Delta G_{rxn}$) for the reactions leading to UB4, UBC, and UB2 formation at varying (a) low – 50, (b) intermediate – 10, and (c) high – 101CO partial pressures. At 1700℃, UB4 and UBC formations remain spontaneous, whereas UB2 synthesis is suppressed under high CO pressure, consistent with experimental observations.
• Figure 3: (a) Effect of sintering temperature on the LXRD patterns of UB4 after 1 of sintering. (b) Effect of sintering duration on the LXRD patterns of UB4 at a fixed temperature of 1500℃. Peaks were indexed against PDF [01-085-4598] for UB4 taken from the International Centre of Diffraction Data (ICDD).
• Figure 4: SEM images of sintered UB4 (top) compared with those of the UB4–UBC composite at different regions of the pellet (bottom). The red regions illustrate the coalescing grains during sintering.
• Figure 5: SXRD patterns showing the temperature-dependent phase evolution of (a) UB4 and (b) UB4–UBC during a step-by-step heating procedure in air. Diffraction patterns are displayed from room temperature to 900℃. Peaks were indexed against PDF [01-085-4598] for UB4, PDF [00-005-0550] for UO2, PDF [01-083-2940] for UB12, Al2O3 from Ishizawa et. al.35, and PDF [04-008-8907] for UBC (ICDD).