The two units at TVO’s Olkiluoto plant undergo annual outages for refuelling, maintenance and modifications during springtime, when a lot of inexpensive hydroelectric power is available. Only one plant unit is shut down at a time.

Outages are divided into two types: refuelling and service outages. A refuelling outage consists of refuelling and repairs, as well as maintenance, inspections and tests scheduled for one-year intervals. Only those plant modifications crucial for operational reliability or forthcoming service tasks are carried out. The typical length of a refuelling outage is around eight days. A service outage, in turn, lasts from two to three weeks and includes major maintenance tasks and widespread plant modifications.

Outages are scheduled so that each year, one plant unit undergoes a refuelling outage while a service outage is carried out on the other. The current sequence is the result of years of development and standardisation. The aim has been to learn new lessons from the progress of each outage, and this trend will also continue in the future.

About once a decade, a longer outage is carried out. Large renovation and modernisation projects are started during these outages. The last large modernisations were carried out during 1997 and 1998, and the next longer outages are scheduled for 2005 and 2006.

Outages are planned and responsibilities are divided beforehand in detail to ensure realisation according to plan. Planning is carried out on three levels. Long-term plans are made about ten years ahead, and they take into account those work tasks with a key effect on the length and costs of the outage. Mid-term planning covers the next three years, and it is used to place preventative maintenance and modifications in the correct outages according to the outage sequence plan. Outage budgets are prepared for the next three years. The next outages are planned hour by hour, down to the very last detail.

Work is carried out with high standards for quality and safety, low radiation doses and optimal costs. The aim is to minimise the amount of unplanned additional work and functional aberrations.

Comprehensive outage reports are prepared, paying special attention to aberrations and improvement proposals. Numeric outage data is gathered for easier comparison.

Lessons learned The first outage was carried out on Olkiluoto 1 in 1980 and on Olkiluoto 2 in 1982. Since then, a total of 44 outages have taken place.

Experience has allowed for activities to be developed and optimised. This development can be seen, among other things, in outage length. In the beginning of the 1980s the total length of the outages was around 50 days, whereas this year it was 20.5 days. At the same time, the annual work amounts have remained the same, with the exception of longer modernisation outages. This is proof of the success in planning and scheduling outage work better year after year.

A total of r350 million has been spent on outages so far. Most of this has been spent on in-house labour and hiring contractor personnel. A total of 17,000 workers have completed around 3000 person work-years of work during the outages. In addition to TVO personnel, about 1000 employees from 100 different contractor companies work at Olkiluoto during the outages. The most part of the workforce comes from neighbouring areas. TVO has aimed at long-term cooperation with the contractors, and yearly employee turnover has been low. The share of short-term workers has reduced since the first outages, being 12 % at the moment.

Contractor employees are housed either at their home, the Olkiluoto housing village, trailer park or a hotel. The Olkiluoto housing village has 400 beds. It also includes three saunas, a washing house, a grillroom as well as kitchen and shower facilities for trailer inhabitants. In addition to the main canteen in the office building, another canteen is opened during outages. Efforts have been made to increase contractor comfort at Olkiluoto by arranging hobby opportunities and leisure time activities. Leisure facilities include jogging trails, a gym, tennis courts, rowboats and a pool table, and there have always been informal competitions, singsongs and fried salmon feasts.

2002 outages

This spring, the outage for Olkiluoto 2 was a refuelling outage. It started on 5 May and ended on 13 May, being the shortest outage at Olkiluoto thus far (seven days seven hours). In addition to refuelling and inspections, significant work tasks included replacing two rotating converters with UPS equipment and strengthening the lower personnel enclosure in the containment building.

The Olkiluoto 1 outage was a service outage, with a length of 13 days and 7 hours. It started on 14 May and ended on 27 May. Significant tasks included – in addition to refuelling, normal maintenance and inspections – the modernisation of the control rod manoeuvring system, process computer interface and the camera surveillance system; replacing two rotating converters in the back-up power system with UPS equipment; altering the mixing point in the feedwater systems; and repairing the generator. The total amount of work carried out during the 2002 outages was about 128 person work-years, and the costs amount to E14.3 million.

The average load factors for the last ten years have been 95.6% for Olkiluoto 1 and 94.9% for Olkiluoto 2. The results are excellent even by international standards. The inspections carried out this year have once again shown the plant units to be in very good condition.