Environmental Engineering Reference
In-Depth Information
Important planes
c
(0001) basal plane
{1010} 1
st
order prism plane
a
3
{1011} 1
st
order pyramidal plane
{1121} 2
nd
order pyramidal plane
a
2
a
1
4.1
HCP crystallographic cell for zirconium alloys, showing the two
major sets of plane: prism planes and, normal to them, the basal planes
(see Schemel, 1989). Reprinted, with permission, from (Tenckhoff,
2005), copyright ASTM International, 100 Barr Harbor Drive, West
Conshohocken, PA 19428.
crystallographic structure. This structure results in signifi cant preferred ori-
entation during fabrication, which results in signifi cant anisotropy of all
properties. Deformation in unirradiated zirconium alloys occurs mainly on
prism planes, as illustrated in Fig. 4.1. During irradiation, dislocation loops
of different types form on prism and basal planes (Section 4.3). Orientation
distributions of the HCP cell are described by 'texture' parameters, which
give the volumetric average orientations of the basal and prism planes in a
particular component. However, this chapter will not explore crystallogra-
phy and fabrication in any detail. Excellent reviews are given by Tenckhoff
( 1988 ); Tenckhoff ( 2005 ); Nikulina
et al
. ( 2006 /2007); Rudling
et al
. (2007);
and Strasser and Rudling ( 2004 ).
4.2
Fuel assembly designs
There are essentially, four different types of commercial light water cooled reac-
tors, whose main characteristics are provided in Table 4.1 (Cox
et al
., 2006 ).
4.2.1 Pressurized water reactors (PWRs) and boiling
water reactors (BWRs)
There is a wide variety of fuel assembly (FA) types for BWRs and PWRs.
The fuel rod array for BWRs was initially 7 × 7 but there has been a trend
over the years to increase the number of FA rods and today most designs
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