Corrosion of Zirconium Alloys

The environments, along with the cracking modes of zirconium and titanium, are given in Table 4.88. It is obvious from the table that zirconium alloys are susceptible to stress-corrosion cracking in a variety of environments. It is necessary to subject the weld to heat treatment in order to lower the stress in the weld. The most serious problem encountered in the nuclear applications is delayed hydride cracking in addition to stress-corrosion cracking, particularly in Zr-2.5% Nb alloy. 

Zirconium alloys are also susceptible to liquid metal embrittlement in metals such as Li, Cs, Cd, Cs/Cd, Cs/Ca, Cs/Y, Cs/Zn, Ag, Hg and Ga and the cracking of the zirconium alloys are transgranular, with the exception in Ga and Cd where the intergranular mode has been observed.105 

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IAEA-TECDOC-996 (1998), Waterside Corrosion of Zirconium Alloys in Nuclear Power Plants, International Atomic Energy Agency, Vienna. 

To help improve the corrosion resistance of Zircaloy, several new zirconium alloys have been developed, such as Zirlo (Zr-1.0% Nb-1.0% Sn-0.1% Fe). Notwithstanding the progress so far, materials reliability does have a significant effect on the economics of nuclear power plants, and there is considerable incentive to develop a full understanding of the mechanisms of corrosion of zirconium alloys in reactors and to develop alloys that are resistant to both irradiation and corrosion in reactors [18]. 

J. Busby, Irradiation effects on corrosion of zirconium alloys, in ASM Handbook, Vol. 13C, Corrosion Environments and Industries, ASM International, Materials Park, OH, 2006, pp. 406-408. See also C. Lemaignan, Corrosion of zirconium alloy components in light water reactors, in ASM Handbook, Vol. 13C, Corrosion Environments and Industries, ASM International, Materials Park, OH 2006, pp. 415-420. 

Figure 2-24. Rates of corrosion of zirconium alloys in boiling sulfuric acid.

S. Kass. 1964. The Development of the Zircaloys in Corrosion of Zirconium Alloys, ASTM STP 3687, Philadelphia, PA American Society for Testing and Materials. D.E. Thomas. 1995. Corrosion in water and steam, in Metallurgy of Zirconium,... 

B. Cox, Some thoughts on the mechanisms of in-reactor corrosion of zirconium alloys, J. Nucl. Mater. 336 (2005) 331-368. 

BURNS W.A. and MAPPEI H.P. Corrosion of Zirconium Alloys ASTM Special Technical Publication No. 368, November 1963. IOI-II7. 

B. Cox, V. G. Kritsky, C. Lemaignan, V. Polley and I. G. Ritchie, Waterside corrosion of zirconium alloys in nuclear power plants, IEAE-TECDOC-996. Vienna IAEA, 1998, p. 249. 

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. 

Heat generation takes place in the reactor core of a nuclear plant (Figure 23.15). The core contains the fuel rods, which consist of fuel enclosed in tubes of a corrosion-resistant zirconium alloy. The fuel is uranium (IV) oxide (UO2) that has been enriched from 0.7% the natural abundance of this fissionable isotope, to the 3% to 4% required to sustain a chain reaction. Sandwiched between the fuel rods are movable control rods made of cadmium or boron (or, in nuclear submarines, hafnium), substances that absorb neutrons very efficiently. 

Parfenov, B. G., Gerasimov, V. V., and Venediktova, G. 1., "Corrosion of Zirconium and Zirconium Alloys," Translated from Russian by Ch. Nisenbaum, Israel Program for Scientific Translations, Jerusalem, 1969. 

H.S. Hong, Y. Yun, K.S. Lee, Corrosion characteristics of zirconium alloy with a high temperamre pre-formed oxide film, J. Alloys Compd. 388 (2005) 279—283. 

Fuel assemblies installed in their channels consist of two subassemblies connected in series. The container type fuel rods are filled with pellets of low enrichment uranium dioxide with the addition of a burnable absorber (erbium). Fuel claddings are made of zirconium alloy (Zr 1% Nb), and channel tubes inside the core are fabricated from another zirconium alloy (Zr 2.5% Nb). Corrosion resistant steel is employed for the inlet and outlet pipelines of the channels outside the core. 

A thorough state of the art literature review on the corrosion of aluminium alloys was compiled by the IAEA in 1998. This review was published in IAEA-TECDOC-1012, Durability of Spent Nuclear Fuels and Facility Components in Wet Storage. It covered a wide range of quantitative and semi-quantitative data on cladding alloys used in nuclear fuel elements and assemblies, and included separate sections on corrosion of aluminium, zirconium, stainless steel, carbon steels and copper alloys in a wet storage... 

Webster, R.T. (1995) Zirconium and Hafnium. In ASM Metals Handbook, 9th ed. Vol. 2 Properties and Selection of Nonferrous Alloys and Special Purpose Materials. ASM, Materials Park OH, pp. 661-721. Webster, R.T. Yau, T.L. (1995) Corrosion of zirconium and hafnium. In ASM Metals Handbook, 9th ed. Vol. 2 Properties and Selection of Nonferrous Alloys and Special Purpose Materials. ASM, Materials Park OH, pp. 707-721. 

Yau, T. L., Stress-Corrosion Cracking of Zirconium Alloys, Stress-Corrosion Cracking, R. H. Jones, Ed., ASM International, Metals Park, OH, 1992, pp. 299-311. 

Corrosion of metals and alloys—Aqueous corrosion testing of zirconium alloys for use in nuclear power reactors... 

Fuel elements have smooth cylindrical claddings of corrosion-resistant zirconium alloy (06.8 mm) structurally similar to that of icebreaker reactor fuel elements. The fuel concept is innovative it is based on the use of uranium dioxide granules in an inert matrix. 

Inconel-625, Incoloy 800) perform better than stainless steel, but still significant corrosion occurs in the presence of HCl, H2SO4 and HNO3, or HF, HBr or HI. Oxidants such as O2 and H2O2 enhance the corrosion of many alloys (stainless steel, Ni-base alloys ). Some improvement is possible by adding Ti, Zr or Al/Nb/Ti to steels. Also, iron-free but very expensive metals like pure titanium or zirconium,or alloys like Monel (Ni- -Cu) and Ti60 have been tested. 

Fig. 2-27 shows the rates of corrosion of Zr-702, Zr-705, and B-3 alloys in boiling solutions of hydrochloric acid. In contrast with the behavior of zirconium alloys in sulfuric and phosphoric acids (Figs 2-24 and 2-26), in hydrochloric acid the rate of corrosion of Zr-705 is lower than that of Zr-702 alloy. Anodic polarization curves of... 

In the nuclear industry, stainless steel was used to clad the uranium dioxide fuel for the first-generation reactors. But by 1965, the force of neutron economy had made zirconium alloys the predominant cladding material for water-cooled reactors. There was a widespread effort to develop strong, corrosion-resistant zirconium alloys. Noticeably, the Ozhennite alloys were developed in the Soviet Union for use in pressurized water and stream. These alloys contain tin, iron, nickel, and niobium, with a total alloy content of 0.5-1.5%. The Zr-1% Nb alloy also is used in the Soviet Union for pressurized water and steam service. Researchers at Atomic Energy of Canada Ltd. took a lead from the Russians zirconium-niobium alloys and developed the Zr-2.5% Nb alloy. This alloy is strong and heat-treatable. It is used either in a cold-worked condition or a quenched-and-aged condition. 

R.F. Koemg. 1953. Corrosion of Zirconium and its Alloys in Liquid Metals, Report No. KAPL-982, prepared for the U.S. Atomic Energy Commission by the General Electric Company. 

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