Plant Materials
DOE-HDBK-1017/2-93
PLANT MATERIAL PROBLEMS
PLANT MATERIAL PROBLEMS
Material problems in a nuclear reactor plant can be grouped into two categories,
one concerning the nuclear reactor core and one that will apply to all plant
materials. This chapter discusses specific material problems associated with
fatigue failure, work hardening, mechanical forces applied to materials, stress,
and strain.
EO 1.14
DEFINE the following terms:
a.
Fatigue failure
b.
Work hardening
c.
Creep
EO 1.15
STATE measures taken to counteract or minimize the effects of the
following:
a.
Fatigue failure
b.
Work hardening
c.
Creep
Fatigue Failure
The majority of engineering failures are caused by fatigue. Fatigue failure is defined as the
tendency of a material to fracture by means of progressive brittle cracking under repeated
alternating or cyclic stresses of an intensity considerably below the normal strength. Although
the fracture is of a brittle type, it may take some time to propagate, depending on both the
intensity and frequency of the stress cycles. Nevertheless, there is very little, if any, warning
before failure if the crack is not noticed. The number of cycles required to cause fatigue failure
at a particular peak stress is generally quite large, but it decreases as the stress is increased. For
some mild steels, cyclical stresses can be continued indefinitely provided the peak stress
(sometimes called fatigue strength) is below the endurance limit value.
A good example of fatigue failure is breaking a thin steel rod or wire with your hands after
bending it back and forth several times in the same place. Another example is an unbalanced
pump impeller resulting in vibrations that can cause fatigue failure.
The type of fatigue of most concern in nuclear power plants is thermal fatigue. Thermal fatigue
can arise from thermal stresses produced by cyclic changes in temperature. Large components
like the pressurizer, reactor vessel, and reactor system piping are subject to cyclic stresses caused
by temperature variations during reactor startup, change in power level, and shutdown.
Rev. 0
Page 27
MS-05
