Environmental Engineering Reference
In-Depth Information
Table 3. The characteristics of influences
Relation
Current Influence
Influence limit
lim
(
TPP
→
NPP
I TPP
→
NPP
I TPP
→
NPP
)
rel
(
)
rel
lim
(
TPP
→ &
T D
I TPP
rel
(
→
T D
& )
I TPP
→
T D
& )
rel
lim
(
NPP
→ &
T D
I NPP
rel
(
→
T D
& )
I NPP
→
T D
& )
rel
lim
(
NPP
→
TPP
I NPP
→
TPP
I NPP
→
TPP
)
rel
(
)
rel
should be considered as a subsystem that influ-
ences other infrastructures. Other example of a
result of the balance violation consequences is
the Sayano-Shushenskaya HPP accident, when it
could not withstand the increasing of load passed
from Bratskaya HPP.
FMECA might be very helpful technique for
formalization of influences to help performing
NPP safety analysis. The traditional FMECA is
the most widely used reliability analysis technique
in the initial stages of system development. It
is performed to assure that all potential failure
modes have been considered. Traditionally, the
criticality assessment is performed by calculat-
ing the failures criticality as a product of failure
severity and frequency:
value to prioritize the possible accident. The
criticality is assessed as
S
i
Crt S
=
Fr S
×
Sev S
×
I
.
(10)
(
)
(
)
(
)
i
i
i
tot
Taking into consideration the mutual influ-
ences between NPP and power grid, we assume
the failure criticality of NPP (power grid) might
be changed as a result of the criticality changing
of power grid (NPP). We introduce the conditional
criticality presented as
*
*
*
*
I S
(
→
S
) :
Crt S S
(
)
=
Fr S S
(
)
×
Sev S S
(
)
i
j
i
j
i
j
i
j
(11)
where
Crt S S
i
(
*
- conditional criticality of
S
i
provided the failure of
S
j
*
;
Fr S S
j
Crt S
=
Fr S
×
Sev S
,
(9)
(
)
(
)
(
)
(
*
-
S
i
fre-
quency changing provided the failure of
S
j
*
;
Sev S S
i
i
i
i
i
j
where
S
i
- NPP (power grid) accident,
Fr
(
S
i
) - ac-
cident frequency;
Sev
(
S
i
) - severity of accident's
consequences.
The traditional FMECA is two dimensional.
In the case when
Crt
(
S
1
)
=Crt
(
S
2
) we need to use
additional information to differ possible accidents.
Therefore, the total influence
I
tot
(
*
S
i
severity changing provided the
failure of
S
j
*
.
Any accident or a failure of the power grid
system leads to the change of criticality of all
related systems. When a failure of one system
occurs, our approach recalculates the criticalities
of all dependent systems. In case of criticalities
growth, when it goes through the diagonal of
criticality matrix and reaches its margin values,
j
S
i
characterized
by direction and strength might be used as third
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