Properties of zirconium alloys and their applications in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 155

0.8

Zry-2
NSF
E635

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0 0

5 10

Damage dose, dpa

15 20 25

4.63 Irradiation growth of specimens at 320 ° C (593K) in the BOR
60 reactor. 20 dpa is equivalent to about 13 × 10 21 n/cm 2 in a BWR/
PWR. NSF and E635 alloys are nominally Zr1Nb1Sn0.35Fe alloys
(Kobylyansky et al., 2007).

Zircaloys. The fl uence to breakaway is not yet well defi ned but is probably
at least 1.5 × 10 22 n/cm 2 , E >1 MeV (see Fig. 4.63) corresponding to a burnup
of about 75 MWd/kgU.

Temperature during irradiation

The temperature of a component during irradiation is an important variable. In
a BWR, temperature variation along the length of the core is relatively small:
water rods and spacers are near the temperature of the boiling water (288°C,
561K); fuel cladding material operates at slightly higher temperatures due to
heat generation from the fuel and buildup of oxide and crud; but the range is
between 288°C (561K) and 320°C (593K). However, in a PWR the components
all operate with a substantial axial temperature gradient due to increase in the
water temperature as it rises through the core. Depending on core design and
duty, material temperatures could be as low as 280°C (553K) at the bottom and
nearly 400°C (673K) at the top of the core. Therefore, the temperature depen-
dence of irradiation growth and creep must be accounted for.
Growth as a function of temperature is not straightforward, as shown
schematically in Fig. 4.65 (Holt, 1988) for RXA Zircaloy. In general for
Zircaloy at low fl uence, growth decreases with increasing temperature and
at high fl uences growth increases with temperature, with the critical tem-
perature ( T 1 in Fig. 4.65) being near 360°C (633K). It is seen that at less
than about 2 × 10 25 n/m 2 ( E >1MeV) (which is before the region of break-
away growth and before c-component dislocations form) growth peaks at
about 300°C (573K) and then steadily decreases at higher temperatures. At
post-breakaway fl uences, growth rate (the slope of the growth vs fl uence

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