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

KAINULAINEN Erja (ed.). Regulatory oversight of nuclear safety in Finland. Annual report 2011.
STUK-B 147. Helsinki 2012. 108 pp. + Appendices 70 pp.
Management review
The Finnish nuclear power plants caused no danger to the plant environment or employees
in 2011. No events with safety implications to the safety of the environment or people took
place at the plants. The collective radiation doses of employees were low and the radioactive
releases into the environment very small. Radioactive waste generated in operational
processes at the nuclear power plants accumulated as anticipated. Its processing and final
disposal in underground facilities took place in a controlled manner.
STUK-B 147
Keywords: nuclear energy, nuclear facility, nuclear waste, nuclear safeguards, regulatory oversight,
indicators
The number of events reported to STUK was lower than in previous years. The underlying
reasons for the events occurring during the year were mainly related to ageing of the
plants. Ageing-induced faults were detected at both plants, among others in emergency
diesel generators used for ensuring the power supply of safety systems in a situation where
connection to other sources of electricity has been lost. Ageing-induced faults were also
detected at the Olkiluoto NPP in the main valves of the reactor overpressure protection
system. The detected faults have not prevented the operation of safety functions, but following
the observations, STUK required both power companies to investigate and report
on the sufficiency of condition monitoring, preventive maintenance and management of
spare parts of the safety system equipment and structures. Furthermore, STUK inspected
the spare parts management of plants, as well as their condition monitoring and licensee
inspection activities during the annual maintenance outages. The inspections and operating
experience show that the Loviisa and Olkiluoto plants have to pay more attention to
the monitoring and management of ageing of safety systems.
At Loviisa and Olkiluoto, modifications required for improving safety continued regarding
plant systems, equipment and structures and operating practices. At Loviisa 1, the suction
strainers of the low-pressure emergency cooling system and containment spraying
system, required in accident situations, were improved by installing smaller-mesh strainer
elements. The modification will secure the cooling of fuel by preventing loose insulation
materials, for example, from entering the reactor core through the emergency cooling
system in an accident situation. A similar modification was carried out at Loviisa 2 the
year before. The Olkiluoto plant continued the modernisation project spanning many years,
aimed at extending the service life of the plant and improving its availability. Most of the
modifications implemented at Olkiluoto 1 in 2011 were now implemented at Olkiluoto 2.
TVO also started the work for expanding the spent nuclear fuel storage in Olkiluoto. At the
same time, the structures of the storage facility will be modified to comply with the current
safety requirements.
Following the Fukushima accident, national safety assessments were initiated and implemented
at both pants. They involved assessing the safety of the plants and their safety
margins against external threats, such as floods, earthquakes and extremely rare and
severe weather conditions. The assessments also analysed emergency response activities in
accident situations involving more than one plant unit, as well as cooling of the reactor and
fuel pools in a situation where the plant has lost its power supplies or its normal residual
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