OL1 nuke plant resumes power generation after outage

The Olkiluoto 1 (OL1) nuclear power plant resumed power generation early Tuesday morning after completion of the annual outage, said the owner of the plant Teollisuuden Voima Oyj (TVO) in a press release.

The outage ended at 03:27 a.m. when the unit with 890 MW power generation capacity was connected to the national grid.

The annual outage was this year a longer service outage. The most important activities carried out during the outage included repair work on the front chamber of the turbine condenser, upgrading of reactor I&C, maintenance activities on the high-pressure turbine, replacement of electrical penetrations in the containment, as well as a pressure test of the primary circuit.

In addition to TVO's own personnel, about 1,400 employees of subcontractors took part in the annual outage works this spring.

“The OL1 outage was exceptionally significant this year. It was one of the longest annual outages in the unit’s history and involved a substantial amount of extensive work critical to plant safety and reliable electricity generation. The OL1 outage began on April 19 and lasted for 57 days and 9 hours,” said Marjo Mustonen, Director of Electricity Production.

On 27 April during the annual outage, water was discharged from a valve onto staff members carrying out maintenance activities, with three employees exposed to reactor cooling water.

The employees and the work area were immediately cleaned and the radiation doses caused by the incident remained very low causing no risk to the employees, the plant or the environment.

Meanwhile, at OL2, this year’s outage was a shorter refuelling outage. It started on 6 April and took a total of 10 days and 18 hours.

When modifications were carried out related to the reactor level measurement system at OL2 on 8 April during the annual outage a protection function was inadvertently activated. The situation was quickly brought under control, the plant restored in normal state and the incident did not cause any risk to the personnel, plant safety, or the environment.

During the annual outage at OL2, on 11 April, a nonconformance was spotted during the transfer of spent fuel, where two doors along the transport route were simultaneously open.

The fuel handling process was immediately discontinued and the incident did not affect radiation safety or the environment. The preliminary INES* rating of the incident is 0.

At moment, all three plant units are in normal electricity production after the service outages. For the Olkiluoto 3 plant unit, this year’s annual outage will take place in the autumn.