Uranium-molybdenum alloy

A small fast reactor is used as a power source, the core of which contains more than 30 fuel rods. The fuel is a highly enriched uranium-molybdenum alloy. Longitudinally movable control rods are placed in the beryllium side reflector. 

Experiments and Calculations on Unmoderated Uranium—Molybdenum Alloy Critical Assemblies, J. T. Mihalczo and W. E. Kinney (ORNL). 

The Fermi Core B will contain plates of fully enriched HO,-stainless cermet clad in stainless steel, with an available volume of 600 liters. The radial blanket has a depleted uranium-molybdenum alloy the axial blanket is depleted UO,. 

Fuel elements of larger inner diameter used at Unit 2 compared to that of Unit 1 allowed to lower heat flux and hydraulic resistance. With the equal outer diameter (20 mm), fuel elements inner diameter of the BWs at Unit 1 were 9.4 x 0.6 mm while that of Unit 2 were 12 x 0.6 mm. Diameter of the central tube for feeding the coolant was also increased. There were no other differences in the BWs construction used at BNPP Units 1 and 2. Uranium—molybdenum alloy with magnesium filler was used as fuel in the BWs. 

Tc is available through the /l -decay of Mo (Fig. 2.1.B), which can be obtained by irradiation of natural molybdenum or enriched Mo with thermal neutrons in a nuclear reactor. The cross section of the reaction Mo(nih,v) Mo is 0.13 barn [1.5], Molybdenum trioxide, ammonium molybdate or molybdenum metal are used as targets. This so-called (n,7)-molybdenum-99 is obtained in high nuclidic purity. However, its specific activity amounts to only a few Ci per gram. In contrast, Mo with a specific activity of more than in Ci (3.7 10 MBq) per gram is obtainable by fission of with thermal neutrons in a fission yield of 6.1 atom % [16]. Natural or -enriched uranium, in the form of metal, uranium-aluminum alloys or uranium dioxide, is used for the fission. The isolation of Mo requires many separation steps, particularly for the separation of other fission products and transuranium elements that arc also produced. 

Several types of nuclear fuels based on uranium or uranium alloys have been fabricated and tested. Among these, uranium-aluminum alloys are probably the most popular, but alloys of uranium with molybdenum (U-Mo), U-Mo-Pt, U-Nb, and U-Mo doped to 1% with several other elements have been tested (Hofman et al. 1998). There are also alloys with U-Zr and U-Si, not to mention mixed oxide fuels like MOX (with plutonium oxide) or uranium with other actinides. 

To improve these undesirable charactmstics of the metalhc uranium, uranium alloys such as uranium—aluminum, uranium—magnesium, and uranium—molybdenum have been developed (Ma, 1983). Metalhc fuels have been used in some power reactors and research reactors with relatively low operating temperatures. For instance, a uranium ahoy has been used in Magnox reactors (Simnad, 1992). Magnox reactors are subject to two design temperature limits at steady state conditions. First, the fuel temperature should be below 660°C. Second, the cladding temperature should be below 420°C (Zakova, 2012). Metalhc fuels, such as uranium and plutonium fuels, were also used in the first generation of FBRs (Hafele et al., 1970). 

For the preparation of I generators, Te has been isolated both with and without carrier from fission products. In one process (133), the uranium-aluminum alloy was dissolved in nitric acid, tellurium carrier added, and the tellurium (and Mo also) adsorbed on an alumina column. The molybdenum was eluted from the column with dilute aqueous ammonia and then the tellurium with dilute sodium hydroxide. Following acidification of the tellurium-containing eluate with hydrochloric acid, the tellurium was reduced to the free state by sulfur dioxide. It was then dissolved in nitric acid and again placed on an alumina column. The column was milked for I with 0.01 M aqueous ammonia. 

In the determination of molybdenum in uranium alloys containing 2.5% molybdenum,20 the uranium had to be removed because its high absorbance made the method insensitive. After a single solvent extraction, the molybdenum could be determined with a standard deviation... 

Phillips and Timms [599] described a less general method. They converted germanium and silicon in alloys into hydrides and further into chlorides by contact with gold trichloride. They performed GC on a column packed with 13% of silicone 702 on Celite with the use of a gas-density balance for detection. Juvet and Fischer [600] developed a special reactor coupled directly to the chromatographic column, in which they fluorinated metals in alloys, carbides, oxides, sulphides and salts. In these samples, they determined quantitatively uranium, sulphur, selenium, technetium, tungsten, molybdenum, rhenium, silicon, boron, osmium, vanadium, iridium and platinum as fluorides. They performed the analysis on a PTFE column packed with 15% of Kel-F oil No. 10 on Chromosorb T. Prior to analysis the column was conditioned with fluorine and chlorine trifluoride in order to remove moisture and reactive organic compounds. The thermal conductivity detector was equipped with nickel-coated filaments resistant to corrosion with metal fluorides. Fig. 5.34 illustrates the analysis of tungsten, rhenium and osmium fluorides by this method. 

This volume is devoted to the four elements chromium, molybdenum, tungsten, and uranium. The study of each of these provides much that is fascinating to the chemist, and much that calls for elucidation and further research. The growing importance of the metals and their compounds in industry, especially in the manufacture of steels and special alloys, and in the production of glazes and pigments, emphasises their claims to interest. The use of tmigsten in electrical work is continually finding wider application. 

Microgram amounts of TcOj can be ascertained by measuring the absorbance of the colored complex, formed with toluene-3,4-dithiol in 2.1 M HCl, after extraction into carbon tetrachloride. One hour must be allowed for the development of the color. ITie molar absorbance index at 410 nm is 1.1-10" mole -1-cm. Beer s law is followed over the range of 1.1 to 16.1 pg Tc/ml. Because many cations interfere, an initial separation of technetium is necessary [73]. The same complex was used for the determination of technetium in uranium fission element alloys after separation of Tc by distillation from sulphuric acid [74j. I hc complex formation of technetium, rhenium, and molybdenum with toluene-3,4-dithiol and its analytical application have been studied in detail [71]. 

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