Environmental Engineering Reference
In-Depth Information
Table 1.3 LWR components, key materials, problems and causes
Component
Key materials
Major issues
Primary causes
Fuel
cladding,
assembly
and
channel
(BWRs)
Zircaloy/UO 2
Cladding
perforation
Dimensional
changes
Bowing and
dilation
Pellet cladding interaction (PCI)
Oxidation, corrosion, hydriding
Creep
Swelling
Grid-to-rod fretting (GTRF)
Crud formation
IGSCC and IASCC
Shadow corrosion (BWR
channels)
Control rod
304 SS/B 4 C,
AgInCd
Perforation
Leachout
Stress corrosion cracking
(SCC)
Pressure
vessel
Low alloy
steel
Integrity in
presence of
cracks
Radiation embrittlement
Corrosion fatigue
Piping
304 SS
(BWRs)
C steel
(PWRs)
Cracking
Distortion
Corrosion
Stress corrosion cracking
(SCC)
Condenser
Cu-Ni alloys
Tube failures
SCC
Corrosion
Turbine
NiCrMoV
bainitic steel
12Cr SS
Rotor bursts
Disc cracking
Blade cracking
Fatigue
Temper
embrittlement
IGSCC
Corrosion fatigue
SCC
these various possibilities the reactor vendors select different materials for the
construction of the structures in LWRs and it is very interesting to follow the
history of the development of LWR fuel cladding that resulted in the adoption
of Zr-based alloys such as Zircaloy-2 for BWRs and Zircaloy-4 for PWRs. 4
Table 1.3 provides a summary of the reactor components, the key materi-
als, the major materials-related problems and the primary causes of failure. 3
These materials face different environmental parameters whose severity
varies with location. This leads to differences in their ageing mechanisms
and the intensity of their degradation. It is possible that one mechanism
can be a precursor to another, leading to unexpected early failure of the
material. The common ageing-related degradation can be classifi ed as due
to radiation embrittlement, loss of toughness, time dependent deforma-
tion (creep), fatigue, radiation growth, thermal ageing, corrosion, oxida-
tion, stress corrosion cracking (SCC), intergranular and irradiation assisted
stress corrosion cracking (IGSCC/IASCC). The dominant mechanism for
the different structures will vary with environments. These phenomena are
described in the sections which follow.
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