Environmental Engineering Reference
In-Depth Information
Figure 22. Reliability block diagrams of single-channel three-track redundant system
Figure 23. Dependence of P 1D , P 2D , P 1M and P 2M on the time (for systems with diversity β=0,1)
Figure 25 shows a dependence of Δ P 2M-1M (the
difference of probabilities P 2M and P 1M ) and Δ P 2M-2D
(the difference of probabilities P 2M and P 2D ) on
time.
It should be noted that, although the single-
channel two-version three-track redundant system
has the greater effect of the use of diversity, its
application in many ways violates the principle
of independence. Therefore, the use of such an
architecture for safety systems of nuclear power
plants is complicated.
Diversity Metrics: β-Factor: To assess a prob-
ability of a common cause failure, it is necessary
to calculate the metrics for different CCF vulner-
abilities (Figure 26). Circles of these diagrams
correspond to sets of version defects (faults)
causing failure. For one-version (one-channel)
system (Figure 26, a) a number of faults equals
N ( N = Card F ) and any fault of set F is fatal
(equivalent of CCF). In this case metric of CCF
β determining relation of a number of CCFs to a
total number of failures equals 1 (and α =β = 1).
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