THE development of zirconium and its  alloys  for use in nuclear reactors began in the United Statesin  1948 when 

it was found that hafnium-free zirconium had a much lower neutron-absorption crosssection than had previously been suspected. Structural materials  for  use in water-cooled power reactors must possess  a  combination of high stre-ngth, corrosion resistance and low neutron capture cross-section. Zirconium alloys alone have the required combi-nation  of  these. For  almost  a  decade  the  standard 

zirconium alloy for use in water-cooled reactors has been

zircalov-2. A very  considerable  body  of experience in

the fabrication  and  use  of zirconium  alloys has been

built up. It has been demonstrated  that  zircaloy tubes

can be manufactured to specifications  far more exacting

in their requirements than  is  the  case  for  standard

code  specifications for  heat  exchanger  and condenser

tubes

Moorthy, K Balarama

English

The development of zirconium and its alloys for use in nuclear reactors began in the United  States  in 1948 when it was found that hafnium-free zirconium had a much lower neutron-absorption cross-section than had previously been suspected. Structural  materials  for  use  in water cooled Power Reactors must possess a combination  capture cross-section. Zirconium alloys alone have  the  required combination of these. It will be fruitful  to  trace very briefly, the history  of  development  of  the  zirconium alloys

Balaramamoorthy, K

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PAPER NC: 5g CURRENT TRENDS IN THE USE CF ZIRCOFTTTY AL-LOYS(*) K. Balarama-moorthy, Atomic Fuels Division,: Bhabha Atomic Research Centre,  Bombay. The development of zirconium and its alloys for use in nuclear reactors began in the United States in 1948 when it was found that hafnium-free zirconium had a much lower neutron-absorption cross-section than had previously been suspected. Structural materials for use in water cooled Power Reactors must possess a combination of high strength, corrosion resistance, and low neutron capture cross-section. Zirconium alloys alone have the required combination of these. It will be fruitful to trace very briefly, the history of development of the Zirconium alloys. Zirconium: The first zirconium base cladding material used was iodide zirconium. It consists of zirconium metal in its purest commercial state, and consequently is very expensive. Furthermore, the corrosion characteristics of this material, although certainly adequate, are sensitive to handling and pickling operations. Zircaloy-1:  The tin addition was found to counteract the dele-terious corrosion effects of nitrogen, carbon and other impurities. This alloy, zirconiun1 sponge plus 2.5 w/o Sn was known as zircaloy-1 (Table I). Experience showed that zircaloy-1 did not possess completely adequate corrosion resistance in water and steam, inthat, rate of adherent oxide film build up was high and cast doubt as to adequate heat removal from zircaloy-1 clad fuel elements. Zircaloy-2: The next development was zircaloy-2 V.-lose compo-sition is given in Table I. This is a sponge base mater-ial to which has been added 1.5 w/o Sn for reasons outlined earlier, with small additions of Fe and Cr for improved •••••••nn•• •7711.n (*) Paper for presentation at the Symposium _on "Recent Developments in Non-Ferrous Metals' Technology" - 4th to 7th December, 1968, Jamshedpur. Not to be reproduced in any media (C) National Metallurgical Laboratory, 'Jamshedpur. -2- 	 1- 26 corrosion resistance in water and steam, and a small amount of nickel for enhancing corrosion resistance in steam. This is the alloy which has seen an extensive use in the nuclear power reactors. Zircaloy-3: Development of zircaloy-3 (Table I) was another step and it contains 0.25% Sn and 0.25% Fe and this alloy never saw an extensive application because of its inferior corrosion characteristics. Nickel Free Zircaloy-2: The nickel free zircaloy-2 (Table I) was developed to counteract'the bad effects of possibility of hydriding and even this alloy does not possess any6ignificant impro-vement over that of zircaloy-2. Zircaloy=4: Bearing the above considerations in mind, zircaly-4 containing 0.24 w/o Fe is developed (Table I) for yielding the same volume of intermetallic phases present in zirca-loy-2 and also - to recapture some of the steam corrosion resistance that might be lost by'removal of nickel. The hydrogen absorption characteristics of modified zircaloy-4 is observed to be definitely superior to Zircaloy-2. Zirconium-Niobium alloy The Russian work reported at the second Geneva Conference strongly suggested that an alloy of zirconium containing 1 to 5 weight per .cent-niobium would have superior mechanical strength and adequate corrosion resistance. From the Russian work and early studies at AECL, an alloy containing 2.4 - 2.8% Nb and 900-1300 ppm oxygen was chosen as representing satisfactory combination of properties and is cornpatable with the manufacturing requirements. a) Fabrication & Mechanical Properties: Zirconium-niobium tubes can be produced in two ways and possess higher mechanical properties than zircaloy-2. Pressure tubes with 3.25" ID(Candu type). have been extruded and cold drawn to about 23% R.A. and the tubes produced by this route will have a minimum tensile strength of 70,000 psi (at 300°C) which is about 30-40% greater than that of zircaloy-2 tube. . . .3. -3- 	 I-26 An alternate method of production is to extrude; quench from about 880°C (depending on oxygen content) into water, draw to size and age at 500°C. This route will produce a tube with an UTS of 90,000 psi (at 300°C) which is about 70% greater than that of zircaloy-2. b) Corrosion The data reported so far indicates that the heat treated Zr-Nb is considerably better than the coldworked material and can give oxidation rates similar to zircaloy-2. From the present evidence it appears that heat-treated zirconium-niobium tubes will oxidize no more in reactor than zircaloy-2 and hydrogen pick up per unit area will be less than that of zircaloy-2. c) Creep: From the creep point coldworked zircaloy-2 is i definitely considered to be nferior to either coldworked or heat treated zirconium-2.5wt% Niobium. Zirconium-Niobium-Copper Alloy Addition of small quantities of copper to the binary Zr-2.5wt% Nb alloy gives a useful reduction to the corrosion rate in air and carbon dioxide. By suit-able choice of solution heat-treatment and aging temperatur0s, tensile properties of the ternary alloy can be made nearly identical to those considered as 6ptimum for the binary alloy. Other Zirconium alloys: Alloys such as Zr-1% Cu-1.5% Mo, Zr-l.25% A1-1% Sn-l% Mo, Zr-0.5% Nb-l%Cr have been investigated for special environment and also as possible substitutes for the Zircaloys and they are yet to gain prominence for the large scale applications in a reactor. /Ahmed: 0 .75 0 •-n cr) r-CI 7J•rl 0 o F-1  CD Fl P N a) U Cri 0 0 rct 0 1 0 rcs 1 0 rcs 1 0 rci 1 COMPOSITION  OF fr, CO w I 0 H • S9 1 	 • O P-t 0 0 . I 	 1 0 00 0 a) 10 	1 	 1 	 • 0 CO C<1'  '41  i 	 I 	 I 	 I 	 I CV CV O4 P4 as o4 P-1 0 0 N. N a4 0 0 P.4 0 1 0 Z N N P-4 LO  H H 14	C\iI 	 I 	 0 	 I 	o 	 0 N CV r-I 	r-♦ 	 r.-I H C\1 ca N di 	! 	 1 	 i 	 1 	 • t '..-- 	o 0 0 0 o o 	 0 	0 	 CD 	 0 	 rx--4 C..) 	 CD 	 Z 	 Z 	F-I 	 F-t 	 F-i 	 i F-i 	 F-I 	 i 	 1 	-r-I 	•r-1 	 •.-1 	 •ri •rl 	 •1•1 	 F-4 	 F-1 N N N Z N N N 0 1000 0.03-0.08 70 1.  0.  0.  0.  0.  0.  0.  0.2  

Current Trends in the Use of Zirconium Alloys

Current trends in the use of Zirconium Alloys

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Current trends in the use of Zirconium Alloys

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