Properties of zirconium alloys and their applications in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 153

CW L-texture

RXA L-texture

0

Fluence

CW T-texture

RXA T-texture

4.61 Schematic curves for irradiation growth as a function of fl uence for
recrystallized (RXA) and CW Zircaloy having textures characterized as
L (f ป 0.1) andT (f ป 0.4) and an irradiation temperature near 300 ° C (573K).

rate is nearly linear with fl uence and the magnitude is almost linear with the
amount of initial CW. In heavily-worked material (typically 70-80% in a fuel
rod) a growth of 2% can be reached by 20 × 10 25 n/m 2 (corresponding to a
burnup of about 100 MWd/kgU). Figure 4.62 gives some values of irradia-
tion growth for Zircaloy materials of different heat treatments, refl ecting the
amount of residual CW and dislocation density. An overview of factors affect-
ing growth is given by Fidleris et al . ( 1987 ).

Texture

￿ ￿ ￿ ￿ ￿ ￿

It can be argued (Hesketh et al ., 1969 ; Alexander et al ., 1977) that the magni-
tude of growth strain in any given direction of a polycrystalline material can
be related to the crystallographic texture and is proportional to a growth
anisotropy factor G d , given by

f c , [4.1]

G f

d

f

d

f c is the resolved fraction of basal poles, f c , in the d -direction. The
anisotropy factor depends on the assumptions that each grain behaves as an
independent single crystal and that the volume change due to irradiation
growth is zero.
At high burnup and high temperature (greater than about 360°C, 633K)
and perhaps also in a heavily cold worked material, the familiar (1−3 f ) and

where f