Pressurized Water Reactor Pressure Vessels
Material from
"Aging and Life Extension of Major Light Water Reactor
Components"
edited by V. N. Shah and P. E. MacDonald
Elsevier, New York, 1993
Introduction
• "In terms of plant safety, the reactor
pressure vessel (RPV) is the most
critical pressure boundary component
in a PWR"
• The RPV ;
1.) Vital safety barrier to fission
product release
2.) Supports and guides control
rods
3.) Supports vessel internals
4.) Provides coolant around the
reactor core
5.) Directs reactor coolant to
steam generator
• 2 Major concerns for the RPV.
1.) Radiation embrittlement
2.) Fatigue
Design and Materials
• Major US Vendors for RPV's
Combustion Engineering (Now part
of a European conglomerate)
Babcock & Wilcox
Westinghouse (via CE and B&W,
Chicago Bridge & Iron,
Rotterdam Dockyard)
• Different design specifications
depending on date of fabrication
Before 1963-ASME Boiler &
Pressure Vessel Code, Sections I
and III.
After 1963-ASME Boiler & Pressure
Vessel Code, Section III.
• Materials
Earliest RPV's used SA302B steel
(Table 3-1)
Most vessels are made from SA533B
(Table 3-1)
Latest RPV's used low Cu/P contents
Inside RPV is lined with stainless
steel (types 304(early), 308 &
309) to reduced corrosion
• Heat Treatments
All vessel welds were post heat
treated at ≈ 610 ± 14 °C for 40-50
hr's (early) and ≈ 25 hr's in the
newer RPV's.
• Diameters
Westinghouse-3.35 to 4.11 meters
Babcock & Wilcox-4.34 meters
Combustion Engineering-3.99 to
4.37 meters
Combustion Engineering System
80- 4.62 meters
• See Figure 3-1
Stressors
• Primary Stressors
Mechanical pressure loads during
operation
Periodic thermal transients
Dead weight loads
Pressurized thermal shock
• Other Important Parameters
Temperature
Water Chemistry
Mechanical Contact
• Ductility is an important measure of
performance
Charpy V-notch---(CVN)
Ductile to brittle transition
temperatures (DBTT)
Upper shelf energies (USE)
(see figure 3-2)
Pressure-Temperature (P-T) Limits
• PWR vessels typically experience
pressures of 15.5 MPa (2250 psi) and
temperatures of nearly 288 °C (550 °F)
during normal steady state operation.
• Perturbations to these conditions are
what set the limits to RPV performance.
• P-T limits require that plants operate
above certain minimum and below
certain maximum limits
Minimum T to be above DBTT
The reactor coolant pump
characteristics govern the
maximum T
• See Figure 3-3
Note: if a critical size defect had been
present at a critical site and the degree of
radiation embrittlement had been severe
enough, this transient might have resulted
in the rupture of the pressure vessel.
• Primary Transients Leading to Fatigue
1.) Plant heatup/cooldown
2.) Plant loading/unloading
3.) Reactor trips
4.) Loss of flow
5.) Abnormal loss of load
See Table 3-2
Degradation Sites
• Beltline region (embrittlement)
Welds may be weakest link because
early welding materials used Cu
coated filler rods
• Geometric discontinuities (fatigue)
Closure studs
Outlet nozzles
Inlet nozzles
Instrumentation nozzles
Control rod drive nozzles
Degradation Mechanisms
• Generally corrosion and stress corrosion
cracking are not a problem in PWR RPV's
because water contains low O2
• Erosion and cavitation not a problem
• High T creep not a problem
Radiation Embrittlement
• Neutron fluence range-
1018 to 1019 n/cm 2 (E> 1 MeV)
• Result for Charpy V-notch (CVN)
specimens:
Increase in reference DBTT (RTNDT)
(usually measured at 41 J [30 ft-lb]
energy, or, T30)
Drop in upper shelf energy (USE)
