Civil Engineering Reference
In-Depth Information
Fig. 5.9
Manipulators for ultrasonic inspection in the hemispherical bottom (
a
) and in the region
of the inlet nozzle (
b
) of the reactor pressure vessel [
2
]
5.6.4.5 Experimental Findings About Pressure Vessel Failure
Within the HSST Program of the Oak Ridge National Laboratory in the United
States [
2
,
19
-
24
], model pressure vessels with large artificial cracks were made to
rupture at high overpressure. However, the vessel material was found to be so tough
in these experiments that major plastic deformation occurred before break. Such
deformations made the cracks applied less sharp-edged, thereby reducing the stress
peaks arising from notch action. Ductile failure without any artificial crack faults
took at least twice the design pressure level.
5.6.5 Reactor Containment
The cooling systems, which carry the high primary coolant pressure of 15.5 MPa,
must be enclosed in an outer containment (Chap.
3
) with the following functions
and capabilities (see Figs.
5.7
and
5.10
):
- In normal operation and under accident conditions, keep releases of radioactivity
into the environment within permissible limits;
- accommodate the heat stored in, and released from, the primary cooling system
in a loss-of-coolant accident and remove it through active cooling systems
together with part of the decay heat (afterheat);
- protect the primary system and steam generators against external impacts.
The design pressure of the containment is determined in terms of its ability to
accommodate all the water released and evaporated from the primary system (full-
pressure containment). Moreover, the underlying assumption in PWRs is that a
