Uranium thermal properties

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. 

To take advantage of some recent measurements, the high temperature thermal properties of uranium metal have been reviewed. Figure 60 shows a summary of the heat content data. The various studies are in excellent agreement except in the y region. In the absence of any reason why this difference should exist, the reported values were combined and... 

Mitchell and 0 nfe(1971 and 1972) studied the thermal properties of various fluorinated /3-d>ketonates of the rare earths, uranium, and thorium and found the volatility and thermal stability of the chelates were improved when an adduct was formed with some neutral donor. Butts m wl6(1970) and later Sieck inLBatiHi (1972) demonstrated that the separation of the lanthanides as ternary complexes with a fluorinated /8-diketone and TBP or di-n-butylsulfoxide by gas-liquid chromatography was possible. Although this method is reasonably sensitive it has not been demonstrated to be reliable at trace levels of the rare earths. y O Laughlin et al. (l966a,b), reported the rare earths and a number of... 

Many challenging industrial and military applications utilize polychlorotriduoroethylene [9002-83-9] (PCTFE) where, ia addition to thermal and chemical resistance, other unique properties are requited ia a thermoplastic polymer. Such has been the destiny of the polymer siace PCTFE was initially synthesized and disclosed ia 1937 (1). The synthesis and characterization of this high molecular weight thermoplastic were researched and utilized duting the Manhattan Project (2). The unique comhination of chemical iaertness, radiation resistance, low vapor permeabiUty, electrical iasulation properties, and thermal stabiUty of this polymer filled an urgent need for a thermoplastic material for use ia the gaseous UF diffusion process for the separation of uranium isotopes (see Diffusion separation methods). 

The only large-scale use of deuterium in industry is as a moderator, in the form of D2O, for nuclear reactors. Because of its favorable slowing-down properties and its small capture cross section for neutrons, deuterium moderation permits the use of uranium containing the natural abundance of uranium-235, thus avoiding an isotope enrichment step in the preparation of reactor fuel. Heavy water-moderated thermal neutron reactors fueled with uranium-233 and surrounded with a natural thorium blanket offer the prospect of successful fuel breeding, ie, production of greater amounts of (by neutron capture in thorium) than are consumed by nuclear fission in the operation of the reactor. The advantages of heavy water-moderated reactors are difficult to assess. 

Complexes. The structure of an n a charge-transfer complex between quinoxaline and two iodine atoms has been obtained by X-ray analysis and its thermal stability compared with those of related complexes. The hydrogen bond complex between quinoxaline and phenol has been studied by infrared spectroscopy and compared with many similar complexes. Adducts of quinoxaline with uranium salts and with a variety of copper(II) alkano-ates have been prepared, characterized, and studied with respect to IR spectra or magnetic properties, respectively. 

The element was discovered in the pitchblende ores by the German chemist M.S. Klaproth in 1789. He named this new element uranium after the planet Uranus which had just been discovered eight years earlier in 1781. The metal was isolated first in 1841 by Pehgot by reducing the anhydrous chloride with potassium. Its radioactivity was discovered by Henry Becquerel in 1896. Then in the 1930 s and 40 s there were several revolutionary discoveries of nuclear properties of uranium. In 1934, Enrico Fermi and co-workers observed the beta radioactivity of uranium, following neutron bombardment and in 1939, Lise Meitner, Otto Hahn, and Fritz Strassmann discovered fission of uranium nucleus when bombarded with thermal neutrons to produce radioactive iso-... 

Elemental composition (anhydrous compound) U 60.41%, N 7.11%, O 32.48%. The compound may be identified by its physical properties and measured by gravimetric methods from its thermal decomposition to form uranium trioxide, UO3. The radioactivity may be measured by an alpha counter. 

The high-temperature gas-cooled reactor (HTGR) is a thermal reactor that produces desired steam conditions. Helium is used as the coolam. Graphite, with its superior high temperature properties, is used as the moderator and structural material. The fuel is a mixture of enriched uranium and thorium in the form of carbide particles clad with ceramic coatings. 

If metallic irranium is used as fuel, the modifications of the metal and their properties have to be taken into account (Table 11.4). The anisotropic thermal expansion of a-U leads to plastic deformations which restrict the use of metallic uranium considerably. Furthermore, by the difference in the density of a-U and j8-U the applica-... 

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