Civil Engineering Reference
In-Depth Information
7.1 Earthquakes
Nuclear power plants, e.g. in Germany and in other countries must be designed
against vibrations caused by earthquakes. The designs must meet specific design
guidelines [
1
-
10
]. Internationally, a difference is made between [
2
,
11
,
12
]:
• Design basis earthquake:
The nuclear plant must withstand an earthquake undamaged in such a way that it
can be restarted and continue operation after automatic scram. In Germany, for
instance, the probability of this design basis earthquake being exceeded must be
as low as 10
5
per year (statistically, an earthquake exceeding that level would
have to be expected once in 100,000 years) [
6
-
9
].
• Safe shutdown earthquake:
In a safe shutdown earthquake, the fundamental safety functions of the nuclear
power plant must remain fulfilled, i.e. the nuclear power plant must be shut down
safely, and the residual heat must be removed safely. The radioactive materials
must remain safely contained by barrier systems (containment) of the nuclear
power plant.
In Germany, as an example, the guidelines contained in KTA 2201 [
6
,
7
] and the
RSK-LL [
10
] apply. The design basis conditions for earthquakes are defined by
seismologists on the basis of historical data and the tectonic conditions in the
perimeter of the nuclear power plant.
7.1.1 Definition of the Design Basis Earthquake According
to KTA 2201
The design basis earthquake to be assumed is the earthquake of the highest intensity
on the respective site which can occur according to scientific findings, taking into
account a wider environment of the site (up to approx. 200 km around the site).
Since 1935, earthquake intensities according to Richter have been referred to as
magnitudes, M (deflection of the seismograph) at approx. 100 km distance from the
epicenter of the earthquake as determined by several earthquake measuring stations
and by calculation. This is the applicable formula:
M
¼
log
10
A
ð
=
A
0
Þ
with A as the deflection of the seismograph and A
0
as the reference amplitude. An
increase in M by one unit means a tenfold increase in earthquake intensity.
However, the magnitude, M, is not a direct measure of the horizontal and vertical
accelerations and vibration frequencies shaking the nuclear power plant and
subjecting it to mechanical loads and stresses. Moreover, such measurements
