Zirconium alloying element

Additions of selected alloying elements raise the recrystaUization temperature, extending to higher temperature regimes the tensile properties of the cold-worked molybdenum metal. The simultaneous additions of 0.5% titanium and 0.1% zirconium produce the TZM aUoy, which has a corresponding... 

By contrast, uranium fuels for lightwater reactors fall between these extremes. A typical pressurized water reactor (PWR) fuel element begins life at an enrichment of about 3.2% and is discharged at a bum-up of about 30 x 10 MW-d/t, at which time it contains about 0.8 wt % and about 1.0 wt % total plutonium. Boiling water reactor (BWR) fuel is lower in both initial enrichment and bum-up. The uranium in LWR fuel is present as oxide pellets, clad in zirconium alloy tubes about 4.6 m long. The tubes are assembled in arrays that are held in place by spacers and end-fittings. 

In addition to these principal alloying elements, which provide soHd solution strengthening and/or precipitation strengthening, wrought alloys may contain small amounts of titanium and boron [7440-42-8J, B, for control of ingot grain size, and ancillary additions of chromium, manganese, and zirconium to provide dispersoids. AH commercial alloys also contain iron and siUcon. 

Cladding. The Magnox reactors get their name from the magnesium-aluminium alloy used to clad the fuel elements, and stainless steels are used in other gas-cooled reactors. In water reactors zirconium alloys are the favoured cladding materials. 

The corrosion behaviour of amorphous alloys has received particular attention since the extraordinarily high corrosion resistance of amorphous iron-chromium-metalloid alloys was reported. The majority of amorphous ferrous alloys contain large amounts of metalloids. The corrosion rate of amorphous iron-metalloid alloys decreases with the addition of most second metallic elements such as titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium and platinum . The addition of chromium is particularly effective. For instance amorphous Fe-8Cr-13P-7C alloy passivates spontaneously even in 2 N HCl at ambient temperature ". (The number denoting the concentration of an alloy element in the amorphous alloy formulae is the atomic percent unless otherwise stated.)... 

K. Venth, K. Danzer, G. Kundermann and K.-H. Blaufuss, Multisignal evaluation in ICP MS, determination of trace elements in molybdenum-zirconium alloys, Fresenius J. Anal. Chem., 354(7-8), 1996, 811-817. 

Letters indicate ihc Iwo principal alloying elements A, Aluminum E, Rare-Earth H. Thorium K, Zirconium M, Manganese Q, Silver, S, Silicon T, Tin Z, Zinc. Thus HK signifies a thorium-zirconium magnesium alloy. 

The approximate amounls (percent, wt) ol lhe Iwo principal alloying materials follow to the immediate righi of ihe alloying element leliers. Thus HK31 indicares approximately 3% thorium, and 1% zirconium... 

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. 

Even sub-ppm levels of some elements can affect properties and processing of steel and other alloys. The analysis of low- and high-alloy steels for environmentally important elements (Cd, Hg) as well as elements that affect the steel (Sb and Bi, for example) has been discussed [343]. ICP-MS has been used for semiquantitative and quantitative measurement of Gd, Sm, and Th in zirconium alloys [344]. 

The low cross-section for absorption of neutrons and high-temperature (330-350°C) aqueous corrosion resistance as well as its good mechanical properties promote the use of zirconium alloys in the nuclear reactors. In the development of zirconium alloys care must be taken that the added minor elements do not posses high cross-sections for the absorption of neutrons and contribute to greater corrosion resistance and improved mechanical properties. The good corrosion resistance of the alloys in acids and bases favors the use of zirconium alloys in chemical plants. 

Zirconium is known as an alloying element that improves the high temperature properties of Ti-Si alloys via increasing the matrix hardenability as well as through microstructural modification [1-4], The formation of two... 

The major use for zirconium is in the nuclear industry. Zirconium alloys (zircaloys) are used extensively as a cladding for nuclear (uranium oxide) fuel rods in water cooled reactors. Zircaloys were favoured over stainless steel cladding because they had a considerably lower neutron cross-section, appropriate thermal conductivity and both corrosion and mechanical resistance. As indicated, hafnium is an impurity in nearly all zirconium ores. Hafnium, however, has a much higher neutron cross-section than zirconium and, as such, the two elements must be separated prior to using zirconium in fuel rod cladding. For many years the separation was very difficult due to the chemical similarity of the two elements. Zirconium hydride is used as a moderator in nuclear reactors. 

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