Field Programmable Gate Array Technology for NPP I&Cs - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 142

Figure 12. Combined usage of dependability analysis techniques

lyzed in FMECA only if they produce component
failures; external influences that do not produce
component failures (but may still produce I&CS
failure) are often overlooked.
That's why it is not sufficient to use only
FMECA during NPP I&CS analysis.
To take into account external impacts it is pos-
sible to use IMEA (Intrusion Modes and Effects
Analysis). IMEA is a modification of FMECA
that takes into account possible intrusions to the
system, examples of this analysis are shown in
(Babeshko, E. et al., 2010; Babeshko, E. et al.,
2011).
Results of FMECA and IMEA are used during
further FTA (Fault Tree Analysis), RBD / SBD
(Reliability/Safety Block Diagram), CCF (Com-
mon Cause Failure Analysis), and also during
Markov modeling.

Reliability block diagram (RBD) is a graphical
analysis technique, which expresses the concerned
system as connections of a number of components
in accordance with their logical relation of reli-
ability. Safety block diagram (SBD) is a similar
technique that treats safety aspects.
Figure 13 shows RBD and SBD principles.
Set of NPP I&CS components is split into the
following groups:

• Components that can't lead to NPP I&CS

failure Cw.

• Components that can lead to I&CS failure,

but system state would be safe Cnws.

• Components that can lead to I&CS failure,

but system state would be unsafe Cunws.