Uranium alloys, corrosion

Uranium and Uranium Alloys , in J.J. Burke et al, Eds, Physical Metallurgy of Uranium Alloys , Brookhill Publ Co (1976) also see J.C. Bailer et al, Eds, Comprehensive Inorganic Chemistry , Vol 5, Pergamon Press, Oxford (1973), 40-42 26) LJ. Weirick, Corrosion Testing of the General Electric Mantech Gau 8/A Penetrator, SANDIA 76-8055 (1977) 27) W.C. Hanson... 

Electrolytic dissolution in nitric acid has been used at the Savannah River [B22] and Idaho Qiemical Processing plants [AlO, All] to dissolve a wide variety of fuels and cladding materials, including uranium alloys, stainless steel, aluminum, zircaloy, and nichrome. The electrolytic dissolver developed by du Pont [B22], pictured in Fig. 10.4, uses niobium anodes and cathodes, with the former coated with 0.25 mm of platinum to prevent anodic corrosion. Metallic fuel to be dissolved is held in an alundum insulating frame supported by a niobium basket placed between anode and cathode and electrically insulated from them. Fuel surfaces facing the cathode undergo anodic dissolution in a reaction such as... 

The nuclear fuel, U, was to be contained in "sandwiches".consisting of a central sheet of aluminum-uranium alloy, clad on both sides with aluminum to confine the fission products and prevent corrosion of fuel elements. These thin sandwiches were to be coiled into spirals having some clearance (water passage) between successive turns of the spiral, and the spirals would be placed in and secured to aluminum tubes of about 2 in. diameter. About thirty such tubes would make a triangular lattice of about 6 in. spacing. The spirals of fuel were to be removed when the isotope enrichment of fell to about... 

Corrosion Tests on Promising High-Uranium Alloys. . . . ... 

Water Corrosion of Unclad, High-Uranium Alloys -C., R. Breden, A. H, Roebuck... 

Corrosion results to date on the more promising high uranium alloys in the absence of irradiation indicate the following ... 

CORROSION TESTS ON PROMISING HIGH-URANIUM ALLOYS... 

The fifth component is the stmcture, a material selected for weak absorption for neutrons, and having adequate strength and resistance to corrosion. In thermal reactors, uranium oxide pellets are held and supported by metal tubes, called the cladding. The cladding is composed of zirconium, in the form of an alloy called Zircaloy. Some early reactors used aluminum fast reactors use stainless steel. Additional hardware is required to hold the bundles of fuel rods within a fuel assembly and to support the assembhes that are inserted and removed from the reactor core. Stainless steel is commonly used for such hardware. If the reactor is operated at high temperature and pressure, a thick-walled steel reactor vessel is needed. 

W. D. Wilkinson, Uranium Metallurgy, Vol. 1, Trocess Metallurgy, Vol. 11, Uranium Corrosion and Alloys, Wdey-lnterscience, New York, 1962. 

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. 

Extensive work into the corrosion and oxidation of uranium and its alloys has been undertaken over the past decade but much of this is in the form of Ministry and industrial reports which are not necessarily readily available. The present review concentrates on the work published in the normal scientific and technical press. 

Galvanic corrosion reports have emerged from two sources. In the first , the chemical compatibility of uranium carbides and Cr-Fe-Ni alloys was discussed. Evaluation was by thermodynamic modelling and experimental... 

In PWRs, the fuel is U02, enriched typically to 3.3% 235U while for BWRs, the fuel is U02, enriched to 2.6%. (Natural uranium is 0.72% 235U). The fuel elements are clad in Zircaloy, a zirconium alloy that includes tin, iron, chromium, and nickel that prevents fission product release and protects them against corrosion by the coolant. The control rod material in BWRs is B4C, while PWRs have Ag-In-Cd or Hf control materials. 

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. 

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