NPP: Power Grid Mutual Safety Assessment - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 412

variation of risks caused by their failures, is not
considered. Recently, network modeling has been
revived due to computer technology progress and
increase of interest in complex systems analysis.
Achievements in a graph theory for complex sys-
tems analysis are reviewed in (Albert et al., 2002).
A topology of North American Power System is
analyzed. Graph is used as a model in (Albert et
al., 2002). Evaluations, specifying Power System
topology, lack of connectivity, while demounting
vertexes that connect transmitting substations, are
calculated. Two types of power grid safety hazards
are analyzed: random failures and antagonistic
(intentional) attacks.
There are no models that completely describe
all power grid characteristics. Many models cover
their technical aspect. The graph provides only
conceptual view on power grids. It is used for
cascading effect analysis without power flows
consideration. In (Glass, 2005) it is specified
that justification of failure preventive measures
for power grid operation leads to its structure
unimportance in comparison to operating modes.
Large man-made disasters happen due to cascad-
ing failures.
Some methods used for PG safety analysis
are qualitative and based on expert evaluations.
Analysis results are represented in the form of
risk matrix containing failure effect frequency
and severity. Qualitative techniques of the safety
analysis do not operate numeric data providing
results as descriptions, recommendations. The
safety assessment is related to a qualitative de-
scription of the frequency of undesired events,
damage and threat scenario.
In (Moskalenko, 2010) it is specified that safety
of a power grid can be improved by implementing
of process automation in disturbance situations.
Generally, there is a lack of publications de-
voted to development of the power grid safety
concept.
Common disadvantages of mentioned ap-
proaches are as follows:

• Power grid systems safety values are con-
sidered separately. The approaches consid-
ering NPP safety stay apart from approach-
es considering PG safety;
• Power grid safety is considered a static
attribute;
• No consideration provided for mutual in-
luences between power grid systems.

To assure the power grid safety, it is necessary
to consider and thoroughly analyze the nature of
interaction among power grid systems, including
the NPP. The goal of the chapter is to introduce
an approach to power grid safety assessment con-
sidering the different type of influence inside PG
among its systems (in our case related to NPP).
This technique can be useful to evaluate safety of
NPP or PG taking into consideration their mutual
influences.

PRINCIPLES AND TECHNIQUES
OF DYNAMICAL CRITICALITY

CWW-Based Analysis

General Principles and
Stages of Analysis

The technique represented in the chapter can be
considered an essential part of PG risk manage-
ment and can serve as a base for decision-making
to avoid disturbances or minimize the severity of
their consequences considering the interaction
between NPP and PG systems.
The PG safety analysis is carried out taking
into consideration principles of dynamism, hier-
archy, uncertainty, and influence (interaction) of
subsystems.
Principle of dynamical analysis assumes to
record changes of system criticality during the
operation as a result of changes of its states (transi-
tion to state of non-operability). At each stage of
life cycle the criticality assessment specification