Civil Engineering Reference
In-Depth Information
Fig. 6.1
Major steps in a
reactor risk study [
3
]
Table
6.1
shows some data for the frequency of initiating events used in the first
risk studies for a KWU-PWR in Germany [
8
].
Only if components of the safety system fail on a major scale there will be a
release of radioactivity. Figure
6.2
shows a simplified event tree for a loss-of-
coolant accident in a PWR. In this case, the accident is initiated by the break of a
pipe. This pipe rupture is assumed to occur with a frequency of f
m
per reactor year.
The further development of this accident is then mainly determined by the
availability of the electricity power supply. Failure of the electric power supply to
operate the emergency core cooling system (ECCS) is assigned the probability of
p
1
. Since electricity is either available or not, the probability of power being
available and the ECCS functioning properly is (1
p
1
) If there is no electricity
available the ECCS will not work and the core, after having lost its coolant, will
melt down partially or entirely for lack of cooling. In that case, there may well be
major releases of radioactivity into the environment as a result of a failure of the
containment.
