IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
depicted in Fig.3. The FRS for
isolated reactor vault shows
only two dominant peaks
representing the swaying mode
of main vessel (5.1 Hz) and
reactor vault (14.2 Hz). Once
the reactor vault is connected
with the NICB, reactor vault is
mastered by various buildings
in the NICB, due to which the
vault has many coupled
vibration modes. This imposes
many constraints to ensure that
the natural frequencies of
reactor internal are not lying in
the resonance ranges. The
significant effect is the
influence of fundamental
frequency of about 3 Hz which
corresponds to the swaying
mode of the buildings as seen
in Fig.3. In view of the natural
frequencies of core & control
subassemblies and absorber
rod drive mechanisms lying
around 3 Hz, the dynamic
Table 1 : Displacements of absorber rods and control plug
Table 2 : Primary stress intensities
Table 3 : Strain energy generated in the vessels
amplifications become number of analysis / tests
significant and critical from required for the seismic
reactor shutdown point of view. qualification studies.
Further, while the FRS are
nearly the same in the X and Y Apart from FRS, other
excitations in the case of
isolated reactor vault, they are
quite different in the X and Y
important effects are presented
in Table 1, Table 2 and Table-
3, from which it is clear that
directions in the case of there are increases of: (1)
connected vault. This increases radial and axial displacements
15
15
X direction
Y direction
Acceleration - m/s 2
12
9
6
connected
isolated
Acceleration - m/s 2
12
9
6
connected
isolated
3
3
0
0 10 20 30
0
0 10 20 30
Frequency - Hz
Frequency - Hz
Fig.3 Floor response spectra at reactor assembly support for safe shutdown earthquake
26 R&D FOR FBRs