Fuzzy probability on reliability study of nuclear power plant probabilistic safety assessment: A review

Abstrack
Fault tree analysis (FTA) is a graphical model which has been widely used as a deductive tool for nuclear
power plant (NPP) probabilistic safety assessment (PSA). The conventional one assumes that basic events
of fault trees always have precise failure probabilities or failure rates. However, in real-world applica-
tions, this assumption is still arguable. For example, there is a case where an extremely hazardous
accident has never happened or occurs infrequently. Therefore, reasonable historical failure data are
unavailable or insuf
fi
cient to be used for statistically estimating the reliability characteristics of their
components. To deal with this problem, fuzzy probability approaches have been proposed and imple-
mented. However, those existing approaches still have limitations, such as lack of fuzzy gate represen-
tations and incapability to generate probabilities greater than 1.0E-3. Therefore, a review on the current
implementations of fuzzy probabilities in the NPP PSA is necessary. This study has categorized two types
of fuzzy probability approaches, i.e. fuzzy based FTA and fuzzy hybrid FTA. This study also con
fi
rms that
the fuzzy based FTA should be used when the uncertainties are the main focus of the FTA. Meanwhile, the
fuzzy hybrid FTA should be used when the reliability of basic events of fault trees can only be expressed
by qualitative linguistic terms rather than numerical values.