Light Water Reactor Design Against External Events - The Risks of Nuclear Energy Technology - page 151

Frequency (Hz)
Fig. 7.2 Typical ground response spectra for a reactor building (damping, D, as a parameter) [ 22 ]
displacements and accelerations as well as the seismic forces (loads) and frequen-
cies for the different floors of a reactor building (floor response spectra).
Figure 7.3 shows the example of three-dimensional results (magnified scale) for
the displacements of and in the reactor building caused by horizontal seismic
accelerations [ 23 , 24 ].
The vibration characteristics and the failure, if any, of components, pipes,
switchgear, and cable ducts (Fig. 7.4 ) can be derived from this solution (KTA
2201.4 [ 8 ]). In addition to the calculations performed, internal components of
reactors also were tested on vibrating tables (in Japan, components weighing up
to 1,000 ton) [ 21 ].
As an example German nuclear power plants (pre-konvoy PWR, konvoy-PWR
and BWR-72) on the average have been designed to design basis earthquakes of
intensity levels VI to VIII (Table 7.3 )[ 25 ]. However, they can withstand at least an
earthquake one intensity level higher, and can be shut down safely under those
conditions [ 25 ].
According to KTA 2201.5 [ 6 , 7 ], nuclear power plants must not only have
sensors for scramming the plant but also seismic instruments recording accelera-
tions in an earthquake and, after the seismic event, allowing a comparison to be
made with the assumptions in the design basis earthquake [ 9 ].
7.1.2 Seismic Loads Acting on Components in Nuclear
Power Plants
After calculating and defining the seismic forces acting on the components of a
nuclear power plant (steam generators, pumps, pipes etc.), the mechanical loads in
these components due to earthquakes must be determined. Mechanical stresses