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Melting point: 2,865 °C (5,189 °F; 3,138 K) ... Uranium dioxide or uranium(IV) oxide ... The thermal conductivity of zirconium metal and uranium dioxide as a ...
The metal uranium forms several oxides: Uranium dioxide or uranium(IV) oxide (UO 2, the mineral uraninite or pitchblende) Diuranium pentoxide or uranium(V) oxide (U 2 O 5) Uranium trioxide or uranium(VI) oxide (UO 3) Triuranium octoxide (U 3 O 8), the most stable uranium oxide; yellowcake typically contains 70 to 90 percent triuranium octoxide)
Because the melting point of uranium dioxide is about 3300 K, it is clear that uranium oxide fuel is overheating at the center. Temperature profile for a 20 mm diameter fuel pellet with a power density of 1000 W per cubic meter.
One advantage is that uranium nitride has a better thermal conductivity than UO 2. Uranium nitride has a very high melting point. This fuel has the disadvantage that unless 15 N was used (in place of the more common 14 N), a large amount of 14 C would be generated from the nitrogen by the (n,p) reaction.
At 1,800 °C (3,270 °F), the cladding oxides melt and begin to flow. At 2,700–2,800 °C (4,890–5,070 °F) the uranium oxide fuel rods melt and the reactor core structure and geometry collapses. This can occur at lower temperatures if a eutectic uranium oxide-zirconium composition is formed.
The Gmelin rare earths handbook lists 1522 °C and 1550 °C as two melting points given in the literature, the most recent reference [Handbook on the chemistry and physics of rare earths, vol.12 (1989)] is given with 1529 °C.
As quoted in an online version of: David R. Lide (ed), CRC Handbook of Chemistry and Physics, 84th Edition.CRC Press. Boca Raton, Florida, 2003; Section 4, Properties of the Elements and Inorganic Compounds; Physical Properties of the Rare Earth Metals
The use of pitchblende, uranium in its natural oxide form, dates back to at least the year 79 AD, when it was used in the Roman Empire to add a yellow color to ceramic glazes. [12] Yellow glass with 1% uranium oxide was found in a Roman villa on Cape Posillipo in the Bay of Naples, Italy, by R. T. Gunther of the University of Oxford in 1912. [29]