Civil Engineering Reference
In-Depth Information
Fig. 5.8
Reactor pressure
vessel of a PWR-1300 with
internals [
2
,
4
]
confirmed in experimental programs (Heavy-Section Steel Technology (HSST)
program in the United States [
19
-
27
]).
Unlike the four cooling circuits of a PWR, the reactor pressure vessel cannot be
built redundant (Fig.
5.3
). For this reason, the rules valid today were elaborated
with particular care. A special role in this effort was played by brittle fracture
behavior and the changes in brittle fracture characteristics as a result of welding
processes during manufacture, temperature gradients or materials fatigue due to
corrosion and neutron exposure.
The steel of the reactor pressure vessel or the welds could contain minute cracks
or slag inclusions. When certain stresses in the material are exceeded, such minor
cracks could become unstable (continue to grow larger) and cause the vessel or
other components of the cooling circuits to fail. These problems were clarified
through the development of fracture mechanics techniques [
25
-
30
] and in many
notch impact tests. The change in the so-called NDT (Nil Ductility Temperature)
for assessing notch impact toughness can be verified by advance specimens in the
