Creep deformation of materials in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 72

where A is a constant, the stress, f the texture parameter, d the

grain size, m (~0.4-0.7) and n (~0.8-2) are constants, and the others have
their usual meaning.
As the dislocation density in a CWSR material is high and, as glide but not
climb is the rate controlling mechanism under reactor conditions, the creep
rate of CWSR is higher than that of recrystallized material as shown in the
fi gures. The creep rate (a) increases with increase in the fl ux, (b) increases
with increase in temperature (contribution by thermal creep predominates
above 400°C), (c) is higher along the rolling direction than the transverse
direction, (d) decreases with fl uence (as radiation hardening sets in) and
(e) depends upon the type of alloy (Nb and Sn content increases creep
resistance). The irradiation creep rates of cold-worked Zr-2.5wt.%Nb alloy
are about one-third of those of cold-worked Zircaloy-2 137 at comparable
temperature, stress and fast neutron fl ux while the creep down of HANA
(High Performance Alloy for Nuclear Applications) alloy (after a dose of 12
MWd/Kg U) is half that for Zircaloy-4. 138

ϕ the fl ux, σ

3.9 References

1 . E. N. Andrade , ' On the viscous fl ow in metals and allied phenomena', Proc

Roy Soc Lond A , 84 ( 1910 ) 1 -12.

2 . D. Hanson and M. A. Wheeler , ' The deformation of metals under prolonged

loading: Part I: The fl ow and fracture of aluminum', J Inst Metals , 45 ( 1931 )
229 -257.

3 . G. E. Dieter , Mechanical Metallurgy , New York: McGraw-Hill , 1988 .

4 . J. E. Bird , A. K. Mukherjee and J. E. Dorn , 'Correlations between

high-temperature creep behavior and structure', in Quantitative Relation
Between Properties and Microstructure , D. G. Brandon and A. Rosen (eds)
Haifa, Israel ( 1969 ) 255-342.

5 . J. Cadek , Creep in Metallic Materials , Prague , Czechoslovakia: Elsevier , 1988 .

6 . F. Garofalo , Fundamentals of Creep and Creep-Rupture in Metals , New York :

McMillan , 1965 .

￿ ￿ ￿ ￿ ￿ ￿

7 . W. J. Evans and B. Wilshire , ' The high temperature creep and fracture behav-

ior of 70-30 alpha brass', Metall Trans , 1 ( 1970 ) 2133 -2139.

8 . G. A. Webster , A. P. D. Cox and J. E. Dorn , ' A relationship between transient and

steady state creep at elevated temperatures', J Metal Sci , 3 ( 1969 ) 221 -225.

9 . K. E. Amin , A. K. Mukherjee and J. E. Dorn , ' A universal law for

high-temperature diffusion controlled transient creep', J Mech Phys Solids ,
18 ( 1970 ) 413 -426.

10 . K. L. Murty , ' Biaxial creep of zircaloy cladding ', Trans IIM , 39 ( 1986 )

357 -368.

11 . N. Nir , F. H. Huang , E. W. Hart and Che-Yu Li , ' Relationship between anelas-

tic and nonlinear viscoplastic behavior of 316 stainless steel at low homolo-
gous temperature', Metall Mater Trans , 8 ( 1977 ) 583 -588.

12 . K. L. Murty , ' Creep studies for zircaloy life prediction in water reactors ',

J Metals , Oct. ( 1999 ) 32 -39.