Nuclear fuel UO2 is used mainly as
nuclear fuel, specifically as UO2 or as a mixture of UO2 and PuO2 (
plutonium dioxide) called a mixed oxide (
MOX fuel), in the form of
fuel rods in
nuclear reactors. The
thermal conductivity of uranium dioxide is very low when compared with elemental
uranium,
uranium nitride,
uranium carbide and
zircaloy cladding material as well as most uranium-based alloys. This low thermal conductivity can result in localised overheating in the centres of fuel pellets. The graph below shows the different temperature gradients in different fuel compounds. For these fuels, the thermal power density is the same and the diameter of all the pellets are the same. FuelPellet1.jpg|Uranium oxide fuel pellet RIAN archive 132609 Uranium dioxide fuel pellet starting material.jpg|Starting material containers for uranium dioxide fuel pellet production at a plant in Russia
Color for glass ceramic glaze Uranium oxide (urania) was used to color glass and ceramics prior to World War II, and until the applications of radioactivity were discovered this was its main use. In 1958 the military in both the US and Europe allowed its commercial use again as depleted uranium, and its use began again on a more limited scale. Urania-based ceramic glazes are dark green or black when fired in a reduction or when UO2 is used; more commonly it is used in oxidation to produce bright yellow, orange and red glazes. Orange-colored
Fiestaware is a well-known example of a product with a urania-colored glaze.
Uranium glass is pale green to yellow and often has strong fluorescent properties. Urania has also been used in formulations of
enamel and
porcelain. It is possible to determine with a
Geiger counter if a glaze or glass produced before 1958 contains urania.
Other uses Prior to the realisation of the harmfulness of radiation, uranium was included in false teeth and dentures, as its slight fluorescence made the dentures appear more like real teeth in a variety of lighting conditions.
Depleted UO2 (DUO2) can be used as a material for
radiation shielding. For example,
DUCRETE is a "heavy
concrete" material where
gravel is replaced with uranium dioxide aggregate; this material is investigated for use for
casks for
radioactive waste. Casks can be also made of DUO2-
steel cermet, a
composite material made of an
aggregate of uranium dioxide serving as radiation shielding,
graphite and/or
silicon carbide serving as
neutron radiation absorber and moderator, and steel as the matrix, whose high thermal conductivity allows easy removal of decay heat. Depleted uranium dioxide can be also used as a
catalyst, e.g. for degradation of
volatile organic compounds in gaseous phase,
oxidation of
methane to
methanol, and removal of
sulfur from
petroleum. It has high efficiency and long-term stability when used to destroy VOCs when compared with some of the commercial
catalysts, such as
precious metals,
TiO2, and
Co3O4 catalysts. Much research is being done in this area, DU being favoured for the uranium component due to its low radioactivity. The use of uranium dioxide as a material for
rechargeable batteries is being investigated. The batteries could have a high
power density and a
reduction potential of -4.7 V per cell. Another investigated application is in
photoelectrochemical cells for solar-assisted hydrogen production where UO2 is used as a
photoanode. In earlier times, uranium dioxide was also used as heat conductor for current limitation (URDOX-resistor), which was the first use of its semiconductor properties. Uranium dioxide displays strong
piezomagnetism in the
antiferromagnetic state, observed at cryogenic temperatures below 30
kelvins. Accordingly, the linear
magnetostriction found in UO2 changes sign with the applied magnetic field and exhibits magnetoelastic memory switching phenomena at record high switch-fields of 180,000 Oe. The microscopic origin of the material magnetic properties lays in the face-centered-cubic crystal lattice symmetry of uranium atoms, and its response to applied magnetic fields.
Semiconductor properties The
band gap of uranium dioxide is comparable to those of
silicon and
gallium arsenide, near the optimum for efficiency vs band gap curve for absorption of solar radiation, suggesting its possible use for very efficient
solar cells based on
Schottky diode structure; it also absorbs at five different wavelengths, including infrared, further enhancing its efficiency. Its intrinsic conductivity at room temperature is about the same as of
single crystal silicon. The
dielectric constant of uranium dioxide is about 21.5, which is almost twice as high as of silicon (11.7) and GaAs (12.4). This is an advantage over Si and GaAs in the construction of
integrated circuits, as it may allow higher density integration with higher
breakdown voltages and with lower susceptibility to the
CMOS tunnelling breakdown. The
Seebeck coefficient of uranium dioxide at room temperature is about -750 μV/K, a value significantly higher than the -270 μV/K of
thallium tin telluride (Tl2SnTe5) and
thallium germanium telluride (Tl2GeTe5) other materials promising for applications like
thermoelectric power generation. ==Health dangers==