NPP: Power Grid Mutual Safety Assessment - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 403

the core, a situation that must he avoided under
all conditions. The introduction of new reactor
designs that use passive cooling would alleviate
this problem. Therefore in unreliable grid systems
it is recommended to consider NPP designs with
passive safety systems.
The grid's response over time to the sudden
loss of the NPP can be modeled by computer
simulations, conditioned by the capacity and
interconnectivity of the grid and the size of the
lost NPP generation, as well as the timing of
switching additional power sources to the grid.
Large interconnected electric grids can usually
meet the requirement of providing reliable off-site
power to NPPs connected to the grid. However, in
some scenarios involving poorly interconnected
or controlled electric grids, the sudden shutdown
of a large NPP or any other large generating sta-
tion elsewhere on the grid, might result in severe
degradation of the grid's voltage and frequency, or
even to the collapse of the overall power grid. Simi-
larly, when an NPP is sited on a well maintained
but small and isolated grid of limited generating
capacity (e.g. on an island), the sudden loss of its
generation may lead to the same outcome.

another. This physical reliance could be of
two types: internal and external. The internal
reliance refers to electrical flow between
NPP and other PG's elements. The external
reliance refers to PG's interactions with other
infrastructures. For example a thermal power
plant generating 1,000 mW typically con-
sumes 10 000 tons of coal per day. Under
normal operating conditions the PG requires
natural gas and petroleum fuels for its gen-
erators, road and rail transport and pipelines
to supply fuels to generators, water for cool-
ing and emissions control, banking and fi-
nance for fuel purchases etc.

NPP
inf ( ) : A reliance on infor-
mation transfer between NPP and other ele-
ments of PG (via through I&C systems).
NPP-PG state depends on information trans-
mitted through the information infrastruc-
ture. Informational dependencies connect
NPP and other PG elements via electronic,
informational links.
3. Geographic I

2. Informational I t

NPP ( ) : A local environmental
event affects components of NPP-PG (usu-
ally the transmission lines) due to physical
proximity. Given this influence, events such
as an explosion or fire could create correlated
disturbances or changes in these NPP-PG
elements.
4. Logical I

t

geo

Types of Influences

The NPP as a part of PG constantly interacts with
other elements of PG. All influences (or relation-
ships) existed in PG could be divided into several
hierarchy's levels.
The first level of a hierarchy is a level of in-
teraction between NPPs and TPPs, HPs as other
generating systems. They could interact indirectly
by means of transmission and distribution net-
works. On this hierarchy's level systems influence
each other as a whole.
Generally influences could be classified into
different types (Dudenhoeffer, 2006):

NPP
log ( ) : An influence that exists
between NPP - PG that does not fall into
one of the about categories. Logical depen-
dencies may be more closely likened to a
control scheme that links PG's elements
without any direct physical, informational,
geographical connections (all indirect influ-
ences, example - Moscow blackout 2005
resulted to banking systems disturbances).
5. Organizational I

t

NPP ( ) : Influences though
policy, regulation, markets. The influence
that exists due to a policy or procedure that
relates a state change in one elements of PG

t

org

NPP ( ) : A physical reliance on
materials flow from one infrastructure to

1. Physical I t

phys