IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
Fig.1 PFBR plant layout of NICB
The magnitudes of
displacements and stresses
developed in the structural
systems depend strongly on the
seismic support excitations,
more precisely the floor
response spectra at the support
points (FRS). The dynamic
characteristics of primary
systems, mainly civil structures,
decide the FRS. Adopting the
concept of connected buildings
is one of the means of
mitigating
seismic
amplifications. Accordingly,
the main buildings of nuclear
island viz. reactor containment
building (RCB), steam
generator buildings, fuel
building, control building,
electrical buildings and
radwaste building are
connected carefully giving due
considerations to safety,
economy, operation and
maintenance aspects. RCB
houses the reactor vault which
supports the reactor assembly
and this apart, it contains many
cells at various levels. In the
connected building layout
concept, the connection of
reactor vault with the adjacent
buildings has to be seen
critically. By way of connecting
the reactor vault with the
adjacent cells within RCB, the
reactor vault along with the
reactor assembly gets
connected automatically to the
entire nuclear island connected
buildings (NICB). NICB layout
is shown in Fig.1. With this
connection, the adjacent cells
get support from reactor vault
without calling for additional
structures which helps in
achieving further economy.
However, the adjacent
buildings can influence the
seismic responses of reactor
assembly components
significantly.
In this article, the seismic
responses of reactor assembly
components are quantified
under the two assumptions: (1)
the reactor vault is connected
to the adjacent buildings of
NICB through floor slabs at
three levels as in PFBR (Fig.2a)
and (2) the reactor vault along
with reactor assembly is an
isolated structural system
constructed from base raft
without any connection with the
adjacent buildings within NICB
(Fig.2b). The analysis was
carried out using CAST3M, a
computer code issued by CEA
France.
Effects on connected and
isolated reactor vault
The floor response spectra
(FRS) generated at the reactor
assembly support with and
without connection are
2(a) Connected
2(b) Inter-connected
Fig.2 Reactor assembly mounted on connected and inter-connected reactor vault
R&D FOR FBRs 25