Enhancing Thermal Conductivity of UO2 with the Addition of UB2 via Conventional Sintering Techniques

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Uranium dioxide has been the primary fuel type used in light water reactors for more than 40 years and proven to be reliable and robust. However, the Fukushima-Daiichi nuclear accident has motivated new work evaluating fuels with characteristics promoting accident tolerance, including enhanced thermal conductivity. Recently, additives have been investigated to increase thermal conductivity, but research has been largely focused on non-fissile additions. This study investigated the use of fissile additives to not only increase the thermal conductivity but also increase the uranium loading. Uranium diboride was chosen as the additive for this study due to its promising corrosion behavior as well as its significantly higher thermal conductivity at 573 K (25 Wm−1K−1) when compared to UO2 (7 Wm−1K−1). Uranium diboride powder was fabricated via the arc melting technique and a ball milling process prior to mixing with UO2 in a 90/10 wt% UO2/UB2 ratio. Green bodies were made using a uniaxial die and subjected to a traditional pressureless sintering technique at 2073 K in argon. Sintered samples were analyzed via laser flash analysis for thermal diffusivity and differential scanning calorimetry for specific heat capacity in order to calculate thermal conductivity. The samples displayed an increase of 36–55% in thermal conductivity between 323 and 1273 K when compared to the benchmark samples (pure UO2) as reported in open literature.