### Abstract

Risk measures in various applications of probabilistic
safety assessment (PSA)
are defined and
their use to support operational safety management of
nuclear power plants is
discussed. The
basic risk measures represent the plant risk frequency
(core damage frequency)
either as a static
value - nominal risk frequency or reference risk
frequency - or as a plant
configuration dependent,
dynamic measure - instantaneous risk frequency. Generated
risk measures are
used in
applications. The most significant application, or rather
an objective of PSA,
is the risk
contributor identification in which risk importance
measures are practical.
Other applications as
well as generated risk measures can be seen as advanced
forms of risk
contributor identification
and risk importance measures, respectively.
In the living use of PSA, plant status knowledge is used
to represent actual
plant safety status in
monitoring or follow-up perspective. The PSA model must
be able to express the
risk given a
time and plant configuration. This requires a development
of time-dependent
basic event models.
The basic events can be divided to evident and hidden
events, and the hidden
events can be
further divided to time-independent and time-dependent
events. One problem is
to develop
realistic common cause failure models in this context.
The applicability of the measures should be tested in
order to find a practical
set of quantities for
the result presentation. There might be a danger that too
many measures and
results are
presented. On the other hand, while some measures do not
seem to be applicable
at core damage
frequency level evaluations, they might be descriptive at
system and component
level evaluations.
The risk measures do not only characterize the plant
safety status, but they
reflect the structure of
the PSA model.
A proper use of the measures requires that decision
making criteria are
established. Probability or
frequency based criteria are not sufficient in complex
decision making
situations. They might,
however, give guidance or first indication about the
acceptability of the
decision alternative. An
absolute criterion or measure is perhaps the correct
quantity from the
rationality point of view,
but a relative criterion can be justified due to
uncertainties in PSA.

Original language | English |
---|---|

Place of Publication | Espoo |

Publisher | VTT Technical Research Centre of Finland |

Number of pages | 76 |

ISBN (Print) | 951-38-4384-X |

Publication status | Published - 1993 |

MoE publication type | Not Eligible |

### Publication series

Series | VTT Publications |
---|---|

Number | 146 |

ISSN | 1235-0621 |

### Keywords

- risk analysis
- probability theory
- safety engineering
- assessments
- evaluation
- utilization
- PSA
- operations research
- nuclear power plants
- nuclear energy
- reactor cares
- damage
- failure
- frequencies
- models
- configurations (mathematics)
- decision making
- criteria

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## Cite this

Holmberg, J., Johanson, G., & Niemelä, I. (1993).

*Risk measures in living probabilistic safety assessment*. VTT Technical Research Centre of Finland. VTT Publications, No. 146