Uranium dioxide thermal conductivity

Uranium dioxide UO2 is the form in which uranium is most commonly used as a reactor fuel for light-water, heavy-water, and fast-breeder reactors. It is a stable ceramic that can be heated almost to its melting point, around 2760°C, without serious mechanical deterioration. It does not react with water, so that it is not affected by leakage of cladding in water-cooled reactors. Its principal disadvantages compared with uranium metal are its lower uranium atom density and lower thermal conductivity. At 100°C, thermal conductivities are metal, 0.25 UO2, 0.09 W/(cm-°C). 

There are a variety of advantages to using uranium nitride (UN) over the other fuel types, and a handful of drawbacks that need to be considered. Uranium nitride has a much higher thermal conductivity than uranium dioxide, resulting in a flatter temperature profile across the fuel pin. The same is likely true for uranium carbide, but less testing has been done on uranium carbide than for UN. Figure 3-3 shows the desired thermal properties of UN [Touloukian, 1979]. At the operational temperature, 1300 K, the thermal conductivity is 28.5 W/m-K and the linear expansion is roughly 1%. It is important for the different components to expand at similar rates to minimize the extra stresses. 

Uranium and oxygen uranium atomic ratio by the ignition (gravimetric) impurity correction method CI453 standard test method for the determination of uranium by ignition and oxygen to uranium ratio (0/U) atomic ratio of nuclear grade uranium dioxide powders and pellets Carbon (total) by direct combustion-thermal conductivity method... 

Metal-ceramic (cermet) fuel chosen for the UNITHERM is composed of uranium dioxide particles in a metallic (silumin or zirconium) matrix. Such design is characterized by a high volume ratio of nuclear fuel and, through the use of the metallic matrix, ensures minimum swelling and high thermal conductivity. An optimally shaped cladding is formed when it is filled with the matrix composition. 

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