Regulatory oversight of nuclear safety in Finland. Annual ... - STUK

4.2 OlkiluOtO NPP uNits 1 aNd 2
Operation and operational events
No events leading to a reactor trip occurred at
the Olkiluoto nuclear power plant. In addition to
the annual maintenance outages, TVO shut plant
units down for repairs to a so-called maintenance
outage on three occasions: damaged inner parts in
the valves of the systems required for overpressure
protection of and residual heat removal from the
primary circuit were replaced at both plant units,
and the motor of one reactor coolant pump was replaced
at Olkiluoto 1 due to a bearing fault. Other
significant events included faults in the diesel generators
forming part of the emergency power systems.
The events are described in Appendix 3.
STUK oversaw the operation on a daily basis
at the plant site, by inspecting the regular reports
on operating activities as well as the event
reports, and by making two inspections as part
of the periodic inspection programme. One of the
most significant observations regarding operation
was to do with the activities of operating personnel
during the annual maintenance outages. There
have been several events in recent years where the
operators have reacted slowly to the alarms coming
to the control room during annual maintenance
outages. Similarly, there have been several events
related to component isolation during the annual
maintenance outages. TVO has identified the individual
events, analysed them and determined the
corrective actions. The events have, for example,
resulted in the pumps in safety systems starting
unnecessarily as well as in radioactive systems
being released inside the plant. Due to the recurring
nature and common features of these events,
MW
1000
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700
600
500
400
300
200
100
Olkiluoto 1, 2011
0
1 2 3 4 5 6 7 8 9 10 11 12
100
0
1
Figure 12. Daily average gross power of the Olkiluoto plant in 2011.
900
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700
600
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400
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200
STUK-B 147
STUK required TVO to analyse the events as one
entity and determine the corrective actions and
report the results to STUK in a root cause report
and during an inspection to be conducted in the
spring 2012.
8
7
6
5
4
3
2
1
0
%
100
90
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10
0
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011
INES 1
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011
Olkiluoto 1 Olkiluoto 2
Olkiluoto
Figure 10. INES classified events at the Olkiluoto plant
(INES Level 1 or higher).
Figure 11. Load factors of the Olkiluoto plant units.
MW Olkiluoto 2, 2011
1000
2 3 4 5 6 7 8 9 10 11 12
47