Annual outages

The aim of the annual outages at the Olkiluoto nuclear power plant is to keep the plant units as good as new, to ensure a disturbance-free production capability and to incorporate all lessons learned in the power-generation process so that the operations can be constantly improved. Maintenance and refuelling outages are carried out in alternate years, and the planning of the shutdowns is on a pre-emptive and long-term basis.

The annual outages and the inspections carried out in connection with them have shown that the Olkiluoto nuclear plant units will probably have an operating life of at least 60 years. This means that both units will still be generating electricity in the 2040s.

The annual outages take place in May/June, during which the plant units are refuelled and the necessary maintenance work is carried out. The refuelling outage lasts about one week while the duration of the maintenance outage is usually about two weeks.

A number of modernisation projects have been carried out in both units since the commissioning of the power plant. In the extensive upgrading between 1994 and 1998, the plant units had their generators, low-pressure turbines, and the main transformer replaced and the high-pressure turbines modified. As a result, the output of the two units rose to 840 MW.

During the annual outages of 2005/2006, the biggest ever carried out at Olkiluoto, both reactors had their steam dryers, high-pressure turbines, intermediate superheaters and turbine automation replaced, while the medium-voltage 6.6 kV switchgear was also modernised. As a result, the output of the two units could be raised to 860 MW.

The largest upgradings planned for the next few years include the replacement of the low-pressure turbines and the generators in both units in 2010-2011.

Types of annual outage

The annual outages are in a two-year cycle so that each year, one of the plant units has a refuelling outage, while the other unit undergoes a maintenance outage.

Refuelling outage
A refuelling outage usually lasts for one week and involves refuelling, fault repairs, maintenance work, and inspections and tests that have to be carried out each year. Only modifications that are essential for operational reliability and for future maintenance work are carried out during refuelling outages.

Maintenance outage
A maintenance outage involves refuelling plus all the required large-scale maintenance work and modifications. The duration of a maintenance outage is between two and three weeks.