Original scientific paper
Risk Impact of Maintenance and Other Activities with Regard to Plant Areas
Ivan Vrbanić
orcid.org/0000-0001-8769-1729
; APoSS d.o.o. Repovec 23B, HR-49210 Zabok, Croatia
Ivica Bašić
orcid.org/0000-0002-9496-549X
; APoSS d.o.o. Repovec 23B, HR-49210 Zabok, Croatia
Abstract
In all operating modes of a nuclear power plant a lot of activities take place, including
maintenance, surveillance testing and plant modifications. Some of these activities can impose
temporary increase in risk level, as they may change the status of equipment important to plant
safety. Such risk increases are usually controlled by risk monitoring, which considers changes in
risk due to changes in the status (e.g. availability) of plant systems and functions. Risk monitors are,
in many cases, designed and operated to be system-oriented (or function-oriented), as they focus on
“measuring” the risk associated with different system configurations (from where comes the often
used term “configuration risk management”).
On the other hand, components of plant systems are placed in various locations and at various
floors (elevations) of plant buildings. Piping, as well as cabling, is routed through one or more
buildings. Equipment performing different functions is, sometimes, located near each other due to
architectural limitations. Where required, barriers are applied in order to ensure physical separation
and independency. Due to these reasons, a particular plant area (compartment, room, part of a large
room,…) can contain a variety of mechanical, electrical and / or other equipment with different
safety implications. As well as system components, plant areas are also related to each other, with
different degrees of relative importance. Since activities performed in different plant areas can
imply changes, actual or potential, in the status of associated equipment, structures and / or barriers,
there is also a need that risk monitoring considers the area-oriented aspects, beside considering
those which are system-oriented or function-oriented.
Risk impact of an activity taking place in a particular plant area can be considered in terms of
changes (potential or actual) to its three components: 1) likelihood of initiators which can be
triggered by equipment in the area (but which are not mitigated by any of the equipment in the same
area); 2) mitigating capability regarding the initiators which are not triggered in this area; 3)
likelihood of initiators triggered in this area and mitigating capability regarding the same initiators.
Activity in a particular plant area may be related to none or to any combination of the three risk
impact components. Normally, risk impact under 3) is limited by the architectural engineering
principles (because it may become very large risk contributor). However, it may be present in some
residual form and it cannot be excluded (as demonstrated by area-related risk studies performed in
the past, such as internal fire and internal flooding analyses).
With activity taking place in a particular area, the relevant importance of any other plant area
(and, hence, potential risk impact of any activity that may be planned to go on at the same time) is
then considered in terms of, respectively: 1) whether it contains the equipment relevant for
mitigation of initiators that can be triggered in the considered area; 2) whether it includes the
potential for triggering an initiator which is mitigated by the equipment located in the considered
area; 3) whether it contains the relevant mitigation equipment or include the potential for relevant
initiators.
Keywords
Hrčak ID:
199048
URI
Publication date:
31.7.2017.
Visits: 750 *