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

4.1 Loviisa NPP
The Loviisa power plant intends to reduce the
releases of antimony (Sb-122 and Sb-124) to the
primary circuit and to reduce the activity of the
primary circuit and the resulting radiation exposure.
The power company intends to change the
material of seals in the reactor coolant pumps to
an antimony-free alternative (see Section 4.1.4,
Reactor coolant pump seal).
Radiation doses
The collective occupational radiation dose was 0.43
manSv at Loviisa 1 and 0.29 manSv at Loviisa 1.
According to the YVL Guide issued by STUK, the
threshold for one plant unit’s collective dose averaged
over two successive years is 2.5 manSv per
gigawatt of net electrical power. This means a collective
dose value of 1.22 manSv per Loviisa plant
unit. This limit value was not exceeded at either
plant unit.
The total time used for annual maintenance
outages in Loviisa was short, and there were few
operations of significance for radiation protection,
which resulted in the total collective dose being
the lowest ever in the history of the Loviisa NPP.
The collective occupational radiation doses of employees
at the Loviisa NPP were smaller than the
average doses of employees working in pressurized
water reactors in the OECD countries.
The occupational radiation doses of NPP workers
mostly accumulated in work carried out during
annual maintenance outages. The collective occupational
radiation dose caused by work carried out
during the annual maintenance outages was 0.40
manSv at Loviisa 1, and 0.25 manSv at Loviisa 2.
The highest individual radiation dose accumulated
amounted to 4.9 mSv at Loviisa 1, and to 6.1 mSv
at Loviisa 2. The highest individual dose incurred
during the annual maintenance outages of both
plant units was 7.4 mSv. The highest individual
dose incurred during the year was 7.9 mSv.
The individual radiation dose distribution of
workers at the Loviisa and Olkiluoto nuclear power
plants in 2011 is given in Appendix 2.
Radioactive releases and environmental
radiation monitoring
STUK inspected the operation of the weather
measurement system and environmental radiation
monitoring network at the Loviisa power plant
site. The instruments of the weather measurement
STUK-B 147
system were found to be operable. The environmental
radiation monitoring network had operated
well apart from a few isolated disturbances. Due
to the ageing of both of these systems, the power
plant initiated in 2011 the planning work for upgrading
the weather measurement system and the
environmental radiation monitoring network.
The radioactive releases into the environment
from the Loviisa nuclear power plant were well
below the authorised annual limits in 2011. The
releases of radioactive noble gases into the air
were approximately 6 TBq (as Kr-85-equivalent
activity), which is approximately 0.03% of the
authorised limit. The releases of radioactive noble
gases were dominated by argon-41, i.e. the activation
product of argon-40 present in the air space
between the reactor pressure vessel and the main
concrete shield. The releases of radioactive iodine
isotopes into the air were about 1 MBq (as I-131-
equivalent activity), i.e. approximately 0.0004% of
the authorised limit. The emissions through the
vent stack also included radioactive particulate
matter amounting to 0.1 GBq, tritium amounting
to 0.2 TBq and carbon-14 amounting to approximately
0.3 TBq.
The tritium content of liquid effluents released
into the sea was 15 TBq, less than 10% of the
release limit. The total activity of other nuclides
released into the sea was about 0.2 GBq, which is
In early September 2011, an error was detected
at the Loviisa power plant in the way in which
radioactive emissions were determined. The power
plant had introduced a new gamma activity
measurement system on 11 June 2010, to be used,
among other things, for determining the aerosols
and iodine isotopes in the emissions released into
the atmosphere. Due to an error discovered in the
method used by the new measurement system to
calculate the sampling air flow, the figures reported
to STUK for gamma-active emissions into the
atmosphere had been incorrect during the period
11 June 2010 to 2 September 2011. Having discovered
the error, the licensee reported the matter
to STUK. STUK required the Loviisa power plant
to supply new, corrected figures for the incorrectly
reported emissions.
The event is described in more detail in
Appendix 3.
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