NPP: Power Grid Mutual Safety Assessment - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 407

Figure 4. Relative influences of NPP

stand the defined value of nature's influence. The
earthquake that hit Japan was several times more
powerful than the worst earthquake the nuclear
power plant was built for (the Richter scale works
logarithmically; for example the difference be-
tween an 8.2 and the 8.9 that happened is 5 times).
In the Fukushima nuclear accident the antici-
pated value of influence was exceeded what re-
sulted to accident. Let consider the NPP-Power
grid system shown in Figure 6.
The infrastructure given above could be char-
acterized by some values shown in Table 3.
In this case the conditions of safety for NPP
- Power grid system given above based on the
balance of influence might be written as:

Figure 5. Relative influences on NPP

lim

I TPP ( → NPP ) ≤ I ( TPP → NPP ); ;

rel rel

I TPP ( → T D & ) ≤ I TPP

lim

( → T D & );

rel rel

The different influences on NPP are shown in
Figure 5.
It is worth to note that:

lim

I NPP ( → T D & ) ≤ I NPP ( → T D & );

rel rel

lim

I NPP ( → TPP ) ≤ I NPP ( → TPP ). (8)

rel rel

I

∑

NPP

I = I NPP → SPG ) . (7) (

tot rel i

When the current value of influence between
infrastructures exceeds the acceptable value, it
could result to the state changing of one of them.
The Fukushima nuclear accident proved this
principle of the balance influence. The nature

i

It might be suggested that stability of the NPP-
PG system is provided by the balance of influ-
ences between its elements. The principle of in-
frastructure balance could be taken as one of
major principle infrastructure safety assurance.
The state dynamic is conditioned by changing of
the balance of influences insight the system. The
balance violation leads to state changing of infra-
structure subsystems. According to principle of
hierarchy, any system is a part of other system.
One system S 1 influences another system S 2 with
I

Figure 6. NPP-Power grid system (general)

1 → . In the case when this value exceeds
the certain value I

rel (

S S )

lim (

1 → , it might lead to
state changing of S 2 . The Fukushima nuclear ac-
cident proves this assumption. The NPP might

S S )

rel