Affiliation(s)
1. APOSS d.o.o., Repovec 23B, 49210 Zabok, Croatia
2. Nuclear Science and Technology Department, Brookhaven National Laboratory, Bldg. 130, Upton, NY 11973-5000, USA
ABSTRACT
In using risk-informed approaches for ensuring safety of operating NPPs (nuclear
power plants), risk importance measures obtained from PRAs (probabilistic risk
assessments) of the plants are integral elements of consideration in many
cases. In PSA models and applications associated with NPPs the risk importance
of a particular feature (e.g. function, system, component, failure mode or
operator action) can be, most generally, divided into two categories:
importance with respect to risk increase potential and importance with respect
to risk decrease potential. The representative of the first category, as used
for practical purposes, is RAW (risk achievement worth). Representative of the
second category, as mentioned in consideration of risk importance, is RRW (risk
reduction worth). It can be shown that the two risk importance measures, RAW
and RRW, are dependent on each other. The only parameter in this mutual
dependency is probability of failure of the considered feature. The paper
discusses the relation between RAW and RRW and some of its implications,
including those on the general strategies for the reduction of risk imposed for
the operation of the considered facility. Two general risk reduction strategies
which are considered in the discussion are: a) risk reduction by decreasing the
failure probability of the considered feature; and b) risk reduction while
keeping the failure probability of the considered feature at the same level.
Simple examples are provided to illustrate the differences between two
strategies and point to main issues and conclusions.
KEYWORDS
Probabilistic risk assessment, risk importance measures, risk
achievement worth, risk reduction worth, risk reduction strategy.
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