IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
system are analyzed. Fault Tree
Analysis, shown in Fig.2, is a
Top down approach, where the
failure of system in a particular
mode is taken as top event and
the causes of that failure along
with the interrelation between
the causes are analyzed until
we reach the basic causes.
Apart from these qualitative
methods there are many
quantitative reliability analysis
methods used to compare
different topologies, and
evaluate the probability of
failure on demand.
Calculation of Failure rate
forms the basis for Quantitative
reliability analysis. For
electronic components, US MIL
217-F Notice-2 standard
provides empirical formulae to
find out the failure rate.
Reliability prediction of
electronic components is done
by Parts Stress Method or Parts
Count Method. In case, for any
component, if the failure rate is
not available, failure rate data
given by the manufacturer is
used in the calculations. While
arriving at the failure rate, the
derating of the component,
quality level, temperature and
intended environment are taken
into consideration.
IEC 61508 provides
guidelines for the determination
of probability of unsafe state of
the system. Using these
guidelines, the probability of
unsafe state can be calculated
at different conditions.
Verification and Validation of
the Software and Hardware
should be done to verify
Fig.1 Example Fault Tree model
whether the system is matching
the requirements or not.
The reliability analysis of
Safety Logic Systems and Core
Temperature Monitoring system
proved the safety of the system
theoretically. The results are
used as inputs in the Level 1
Probabilistic Safety Assessment
of PFBR.
V.C.4. Safety Logic with Fine Impulse Test
System for PFBR
PFBR is provided with two
independent, fast acting and
diverse shutdown systems
namely SDS-1 & SDS-2 to
detect any abnormalities in
reactor core and to initiate
safety action. Each system
consists of sensors, signalprocessing
systems, logic
systems, drive mechanisms and
absorber rods. The absorber
rods of the first system are
Control and Safety Rods (CSR)
and that of the second are
called as Diverse Safety Rods
(DSR). There are nine CSR and
three DSR. While CSR are used
for startup, control of reactor
power, controlled shutdown
and SCRAM, the DSR are used
only for SCRAM. The
respective drive mechanisms
are called as CSRDM &
DSRDM. For SDS-1, Safety
Logic with Fine Impulse Test
(SLFIT) System is provided
whereas for SDS-2, Pulse
Coded Safety Logic (PCSL)
System is provided.
SLFIT system receives trip
parameters from neutron flux
monitoring, failed fuel
detection, sodium flow
monitoring, reactor inlet
temperature monitoring systems
130 ENABLING TECHNOLOGIES