Environmental Engineering Reference
In-Depth Information
Gravitational and
hold down force
5.1
Schematics showing FA bowing. Increased GT growth may result
in larger holding down forces (fi gures going from left to right). The fi rst
mode of bowing is B-shape (the second drawing), while the second and
third mode of bowing are S-shape and W-shape, respectively (Strasser
et al
., 2010a).
5.2.1 Bowing
PWR
/
VVER fuel assembly
bowing may occur due to excessive guide tube
(GT) growth that will result in larger holding down forces (Fig. 5.1) (Strasser
et al
., 2010a). The bowing is caused by the complex interaction of a variety
of parameters that include the bowing of the skeleton assembly. The param-
eters include:
GT irradiation growth as a function of fl uence and temperature, see
Section 4.6.1 on irradiation growth.
GT creep as a function of fl uence and temperature, see Section 4.6.2 on
irradiation creep.
GT stiffness and buckling strength as a function of temperature.
The effect of hydrogen pickup and irradiation on the GT properties, see
Section 4.5 on corrosion of zirconium alloys.
Hold-down force.
Thermal expansion of the skeleton components, the core plate spacing
and their interaction.
Fuel rod/grid friction force and relaxation over time.
BWR fuel channel bowing
was studied by Cantonwine
et al
. ( 2009 ).
According to them, channel-control blade interference had been a
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