Environmental Engineering Reference
In-Depth Information
Zry - 2 channel , 43 MWd/kgU
(a)
Oxide
20 m
Away from shadow area
20
m, 300 ppm H 2
(b)
Oxide
20 m
In shadow area
12
m, 150 ppm H 2
4.55 Oxide thickness (a) away from and (b) within a control blade
handle shadow (Adamson et al ., 2000).
￿ ￿ ￿ ￿ ￿ ￿
Figure 4.55 illustrates a 6× difference in oxide thickness within and with-
out of the shadow. It is noteworthy, however, that in this case, hydrogen
content in the shadow is 150 ppm, while outside the shadow it is 300 ppm.
Since temperature gradients are small in a channel wall, redistribution of
hydrogen by thermal-gradient driven diffusion is also small, indicating in
this case a much reduced hydrogen pickup rate in the shadow. More recent
data indicate variability in pickup fraction (HPUF), as (Mahmood et al .,
2010) reported normal HPUF. It is also observed that control blade shadows
preferentially form during the fi rst cycle of operation and that the thickness
tends to saturate with burnup.
Shadows on fuelled or non-fuelled rods have been observed under Zircaloy
spacers with Inconel springs or under all-Inconel spacers (Fig. 4.56). Again,
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