Particular uranium oxide

Data on the yield stress and coefficient of rigidity as a function of concentration for three particular uranium oxide preparations [91] are summarized in Table 4-9. The yield stress-volume fraction solids data may be expressed by a relation of the form... 

Zirconium is used as a containment material for the uranium oxide fuel pellets in nuclear power reactors (see Nuclearreactors). Zirconium is particularly usehil for this appHcation because of its ready availabiUty, good ductiUty, resistance to radiation damage, low thermal-neutron absorption cross section 18 x 10 ° ra (0.18 bams), and excellent corrosion resistance in pressurized hot water up to 350°C. Zirconium is used as an alloy strengthening agent in aluminum and magnesium, and as the burning component in flash bulbs. It is employed as a corrosion-resistant metal in the chemical process industry, and as pressure-vessel material of constmction in the ASME Boiler and Pressure Vessel Codes. 

Since transport by water is virtually the only available mechanism for escape, we will be predominantly concerned with the chemistry of aqueous solutions at the interface with inorganic solids - mainly oxides. These will be at ordinary to somewhat elevated temperatures, 20-200 C, because of the heating effects of radioactive decay during the first millennium. The elements primarily of interest (Table I) are the more persistent fission products which occur in various parts of the periodic table, and the actinides, particularly uranium and thorium and, most important of all, plutonium. 

Strangely enough, a combination similar to the ammonia catalyst, iron oxide plus alumina, yielded particularly good results (32). Together with Ch. Beck, the author found that other combinations such as iron oxide with chromium oxide, zinc oxide with chromium oxide, lead oxide with uranium oxide, copper oxide with zirconium oxide, manganese oxide with chromium oxide, and similar multicomponent systems were quite effective catalysts for the same reaction (33). 

In some systems, particularly metal oxides or nitrides, different states of oxidation of the metal or metals could be assumed or actually determined. Expressions for equilibrium constants related to reactions between the atoms in different oxidation states could be set up in terms of the mole fractions of the reacting species. The expressions for the chemical potentials could also be written in terms of these mole fractions. As an example, consider the substance Uj l,Pul02 x. The question might be to determine how the pressure of oxygen varies with the value of x at constant temperature and constant y. We assume that the uranium is all in the oxidation state of +4 and that the plutonium exists in the +3 and +4 oxidation states for positive values of x. The equilibrium change of state is... 

Heterogeneous catalysis by compounds of uranium, and in particular the oxides of uranium, is well estabhshed and has a long history. The versatility of uranium... 

Tanthanide chemistry is approaching its 200th Anniversary, but except for data on thorium and uranium the chemistry of the actinides is a comparative youngster of some 30 years. However, the two chemistries are intimately associated because their elements are of the f transition type and thus formally comparable with each other and different from other elements. Indeed, these parallels made it possible to unravel actinide behavior in the early days of transuranium element production. In addition to their chemical similarities, the two series also share the properties of magnetism and radiant energy absorption and emission characteristic of /-electron species. However, important differences exist also, particularly in oxidation states, in bonding, and in complex-ion formation. 

Catalysts based on uranium oxide are also particularly active for the destruction of the chlorinated VOCs chlorobenzene and chlorobutane [77]. Both were destroyed by U3O8 at 350°C and 70,000 h space velocity, showing 99.7% and >99.5% conversions respectively. Time-on-line studies for the destruction of 0.12% chlorobenzene at 450°C showed that the catalyst was not deactivated as 99.9% conversion was maintained during 400 hours continuous operation. These catalysts were also active for the oxidative abatement of other VOCs and it has been demonstrated that toluene, butylacetate and cyclohexanone can also be destroyed at relatively low temperatures. Considering the high space velocities employed in these studies, uranium based catalysts are amongst some of the most active oxide catalysts investigated for VOC destruction. 

Rare metal electrolytic processes are frequently carried out in an inert atmosphere of argon or helium, particularly when it is essential for the oxygen and nitrogen contents of the rare metal products to be as low as possible. However, this does not always apply and large quantities of uranium, for example, have been produced by the American Westinghouse Electric Corporation in cells from which air was not excluded. In this case it was even possible to produce metal with a low oxygen content directly by electrolysis of uranium oxide added to a melt. 

Substantial quantities of nomadioactive material may be vaporized from the reactor core during this stage of an accident. In particular, control rod materials and burnable poisons may be vaporised. Constituents of structural materials such as steel and clad alloying agents as well as uranium oxides may be vaporised along with radionuclides. These nonradioactive materials add to the mass of condensable effluents from the core region and can affect the behavior of radionuclides both in the reactor coolant system and in the containment (See Chapter V). 

Normally, 30% to 4S% of the 85 fuel elements in the reactor will be 1.8 w/o plutonium in aluminum, the remainder swaged natural uranium oxide. Three loadings were given particular attention in the critical tests. A two-zone loading contained 36 plutonium elements in the periphery and 49 uranium elements in the center. A three-zone loading contained 30 plutonium elements in a ring... 

Uranium dioxide, UO2, is the compound of choice in many nuclear reactors despite its relatively poor heat conduction properties. This is due to its chemical stability, its high melting point, and the ease of production of well-characterized morphological and physical properties. The complete characterization is described in Chapter 2. Uranium metal and particularly uranium alloys like U-Al, U-Zr, U-Si, and U-Mo are also used as fuel. Their heat conduction is superior to that of uranium oxide but the metal and alloys are less stable chemically. 

Commercial factors can have a considerable impact on the actual costs of nuclear power stations. Also, as the proportion of electricity generated by nuclear plants becomes more significant, it is Important that these plants are technically capable of operating to suit network requirements. The paper describes the particular features of the SGHWR which make it an attractive system for commercial use. The SGHWR can also be built to operate with natural uranium oxide fuel. The differences between the two versions of the system are briefly outlined. 

Because of the technical importance of solvent extraction, ion-exchange and precipitation processes for the actinides, a major part of their coordination chemistry has been concerned with aqueous solutions, particularly that involving uranium. It is, however, evident that the actinides as a whole have a much stronger tendency to form complexes than the lanthanides and, as a result of the wider range of available oxidation states, their coordination chemistry is more varied. 

Ives et al. (79) tended to reject our hypothesis that brown colours of mixed oxides (and in particular less pure NdaOs) are due to traces of praseodymium. However, these authors noted the interesting effect that such dark colours (also of Pro,oaTho.9802) bleach in the reflection spectrum at higher T. It was noted that mantles of NdaOa alone rapidly hydrate to a pinkish powder (carbonate ) in humid air. It is weU-known that -type sesquioxides are far more reactive, and for instance dissolve almost instantaneously in aqueous acid, than cubic C-type samples. Ives et al. 19) also studied the broad continuous spectrum of the orange light emitted from Thi- 11 0 2+2/ where the oxidation state of uranium is rather uncertain. 

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