First annual outage starts at Olkiluoto 3 on Saturday

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The time reserved for the annual outage of OL3 is 37 days. The long duration is explained, for example, by the technical characteristics of the plant type and the large number of periodic tests and maintenance activities to be carried out during the service outage. As OL3 is the largest nuclear power plant unit in Europe, there is a considerable number of components and equipment that need to be serviced.

All in all, the plan for the OL3 service outage includes some 1,900 different work activities with almost 6,500 work phases. In comparison, the work list for the annual outage of OL2, for example, shows about 550 activities with a total of 1,200 work phases.

At OL3, the most important activities apart from refuelling include preventive maintenance on the protection system, software upgrades in the I&C systems, leak-tightness tests on the containment isolation valves, and the maintenance of the pressuriser safety relief valves.

Work is carried out during the service outage in compliance with a precise schedule and around the clock in several shifts.

- Annual outages are large-scale, meticulously planned processes at nuclear power plant units, and the safe execution of the outages to a hight standard requires professional expertise from both TVO’s own employees and subcontractors and the plant supplier. The authorities also play an important role in the successful execution of the annual outage, explains Marjo Mustonen, Senior Vice President, Electricity Production, for TVO.

In addition to TVO's own personnel, this year about 1,400 employees of subcontractors take part in the annual outage works. The majority are Finnish, but a total of 550 experts in special fields arrive also from abroad, especially for the service outage of OL3.

The Olkiluoto nuclear power plant is the most significant producer of electricity in Finland. Last year, about 31 per cent of all of Finland’s electricity was produced in Olkiluoto. OL3, which is the first unit to undergo the service outage, covers about 14 per cent of the demand for electricity in Finland.

At Olkiluoto 2 (OL2), a refuelling outage will start on 28 April and last for about 8 days*. The last one of the plant units is Olkiluoto 1 (OL1) where a service outage with a duration of about 16 days will start on 12 May. All annual outages are expected to be completed by 28 May.

Annual outages are necessary to carry out refuelling and specific maintenance and service activities. At the same time, annual outages play a key role in the long-term lifecycle management of our plant units.

During the first years of operation, Olkiluoto 3 will undergo an annual outage every year but after that, the plant unit can be operated also in somewhat longer operating cycles. At OL1 and OL2, annual outages will be implemented every year also in the future.

*The news has been updated on 7.3. regarding the duration of OL2's refueling outage. Previously, the duration was reported as 11 days.