Security of Safety Important I&C Systems - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 257

The activities, required to implement the ap-
proach, comprise several consequent steps in-
tended for a comprehensive analysis and assess-
ment of I&C systems. They are depicted in Figure
10.

be represented by a single local IMECA table and
each discrepancy inside the gap can be represented
by a single row in that local IMECA table. In this
way, complete traceability of life cycle processes,
appropriate products and inherent properties of
corresponding discrepancies can be achieved. As
a result, the number of local IMECA tables would
correspond to the number of identified gaps, and
the number of rows within each local IMECA
table would correspond to the number of identified
discrepancies within the appropriate gap.
After completing the appropriate columns, for
example on the basis of expert assessment, for all
local IMECA tables, each gap is represented by a
set of discrepancies with appropriate numerical
values. Data within each row of local IMECA
tables reveal, in explicit form, the weaknesses
of the I&C system aspect under assessment: for
example, in terms of safety - system faults and
failures, in terms of security - intrusion prob-
ability and severity.

The key idea of assessment is in the application
of the process-product approach. Therefore, the
life cycle model of I&C systems should include
detailed representation of life cycle processes and
appropriate products. Then, it is possible to iden-
tify problems (or discrepancies) within the
model, i.e. gaps. In general, such gaps may reflect
various aspects of the I&C system, depending on
what system properties are assessed (for example,
safety and security).
Hence, depending on the I&C system aspects
under assessment, each gap should be represented
in a form of a formal description; such a formal
description should be made for a set of discrepan-
cies identified within the gap. The IMECA tech-
nique is the most convenient, in our opinion, to
perform such description: each identified gap can

Figure 10. The principal stages of I&C system assessment