Properties of zirconium alloys and their applications in light water reactors (LWRs) - Materials' Ageing and Degradation in Light Water Reactors - page 142

2 Nitronic 32 was observed not to cause shadows (Andersson et al ., 2002 ).
3 Resistance to shadow formation depends upon inherent corrosion resis-
tance (Andersson et al ., 2002 ; Garzarolli et al ., 2002 ; Shimada et al ., 2002 ).
4 The distance between components is critical. Oxide thickness is a func-
tion of distance. There is a maximum distance above which there is no
effect (a few mm) but there is no minimum distance, including touching
(Chen & Adamson, 1994; Lysell et al ., 2001 ; Andersson et al ., 2002 ).
5 In general, the shadow forms at low fl uence or exposure and thickness
of the shadow saturates with fl uence (Fukuya et al ., 1994 ; Hoffmann &
Manzel, 1999; Andersson, 2000). In unusual cases, perhaps due to spe-
cial microstructure and water chemistry, accelerated shadow corrosion
begins at high fl uence or burnup (Zwicky et al ., 2000 ; Wikmark & Cox,
2001 ; Andersson et al ., 2002 ).
6 Shadow formation requires a nuclear reactor environment and it has not
been possible to reproduce it in laboratory autoclaves (Andersson, 2000;
Garzarolli et al ., 2001). However, use of ultraviolet light in the labora-
tory has been shown to increase electro-chemical potentials between
common components, believed to be related to shadow formation (Kim
et al ., 2010 ).
7 No reports of shadow formation have been made for PWRs or high-
hydrogen cases. BWR hydrogen water chemistry conditions, however, do
allow shadows (Lefebvre & Lemaignan, 1997; Adamson et al ., 2000 ).
8 Thick oxide shadows do not necessarily result in proportionally high
hydrogen pickup and can result in unusually low hydrogen pickup
(Adamson et al ., 2000) or normal pickup (Mahmood et al ., 2010 ).
9 Pre-oxidation autoclaving of Zircaloy does not prevent shadows, but
applying a zirconia layer to Inconel does (Andersson et al ., 2002 ).
10 Shadow corrosion has been observed when the two metals are not in
contact physically and are nominally electrically insulated from each
other. However, in making such observations it has been assumed that
the radiation fi eld has no effect on the conductivity of the insulating
medium.
11 Shadow formation has been reported (Ch â telain et al ., 2000 ; Andersson
et al ., 2002) in a reactor position outside and downstream of the MIT
test reactor core where the neutron and gamma fl uxes are reported to
be near zero. On the other hand, no shadows were reported (Lysell et al .,
2001) in a reactor position outside and upstream of the R2 test reactor
core where the neutron fl ux and gamma power (fl ux) were also near
zero. However, there does appear to be some uncertainty in the actual
gamma intensities in the MIT experiment, so there may need to be a
re-evaluation of the out-of-core results.
12 Shadow formation can be prevented if electrical connection between
the two components is prevented (Lysell et al ., 2005 ).

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