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

4.2 OlkiluOtO NPP uNits 1 aNd 2
4.2 Olkiluoto nuclear power
plant units 1 and 2
4.2.1 Overall safety assessment of
Olkiluoto 1 and Olkiluoto 2
STUK oversaw the safety of the Olkiluoto power
plant and assessed its organisation and personnel’s
competence in different areas by means of reviewing
materials provided by the license holder, carrying
out inspections in line with the periodic inspection
programme and by overseeing operations at
the plant. On the basis of this regulatory oversight,
STUK can state that plant operation did not cause
a radiation hazard to the employees, population or
the environment. Occupational radiation doses and
radioactive releases into the environment were
low and clearly below the prescribed limits. The
licensee has operated the Olkiluoto power plant
in a safe manner and in compliance with the YVL
Guides. Emergency preparedness at the Olkiluoto
power plant is in compliance with requirements.
The processing, storage and final disposal of low-
and intermediate-level waste (so-called plant operating
waste) at the power plant were carried out
as planned.
According to the tests and inspections carried
out, the condition of the containment and the primary
circuit, which prevent the release of radioactive
material into the environment, are in compliance
with requirements. A small fuel leak was detected
at Olkiluoto 2 in 2010. It was located during
annual maintenance in 2011, and the leaking fuel
assembly was removed from the reactor. In August
2011, a new fuel leak was detected at Olkiluoto
2. The monitoring measurements indicate that it
has remained small. The detected leakages are
insignificant for the radiation safety of the environment,
because the radioactivity is contained in the
primary circuit and inside the containment.
STUK approved the licensee’s application for
increasing the average value fuel burn-up in fuel
assemblies to 50 MWd/kgU. In 2011, STUK carried
out a special inspection concerning ageing management
where the sufficiency of spare parts and the
functionality of spare parts management at the
plant units were assessed. The licensee was found
to have taken corrective actions regarding spare
parts management. At the end of November, STUK
received the report of these actions, which it had
requested following the inspection.
STUK-B 147
Plant operation has been systematic and in compliance
with the Operating Limits and Conditions
(OLC) and guidelines. One event affecting safety
was reported at the plant, rated as class 1 on the
international INES scale. In the event, damage
was discovered in the inner parts of the valves in
the systems required for overpressure protection
of and residual heat removal from the primary
circuits of Olkiluoto 1 and Olkiluoto 2, which is
why TVO replaced all damaged parts. A root cause
analysis was also performed on the event. In 2010,
STUK pointed out that there had been too few root
cause analyses. Two were performed in 2011. They
have concentrated on investigating the technical
causes while the investigations on the activities
of the organisation have scope for improvement.
System and equipment failures had a minor safety
implication for the plant. A significant observation
received through international operating experience
activities was related to a fire occurring in the
containment of a Swedish NPP and the blockages
discovered in the containment spraying system in
that connection. Following the event, TVO decided
to update its instructions for containment leak
tightness tests and to extend the scope of tests and
inspections on the spraying system.
The annual maintenance outages of plant units
were implemented as planned in terms of nuclear
and radiation safety. In 2010, STUK required TVO
to develop its planning processes for annual maintenance
and modification works. The situation
regarding documentation to be submitted to STUK
improved slightly in 2011. STUK will continue the
assessment of corrective actions proposed by TVO
in 2012.
During the year, several modifications were
implemented for improving plant safety. The plant
is in the middle of a modernisation project spanning
many years, aimed at extending the service
life of the plant and improving its availability. The
modifications carried out at Olkiluoto 1 in 2010
were also implemented at Olkiluoto 2 in 2011.
They included the replacement of inner isolation
valves in the main steam system, replacement of
low voltage distribution switchgears in one subsystem,
replacement of the low-pressure turbine,
modernisation of the main seawater pumps as
well as replacement of the generator and its cooling
water system. TVO is also in the process of
expanding the spent fuel storage at Olkiluoto. At
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