Finland’s Teollisuuden Voima (TVO) said the EPR reactor at unit 3 of the Olkiluoto NPP (OL3) has started generating power in test mode. The launch of the reactor was successful, although it was delayed for several hours. "It takes a long time for such a large plant to get ready for commissioning," said TVO public relations specialist Johanna Aho. "We are looking forward to energy production starting," she added.

During the trial operation period, the nuclear power plant will conduct a series of 10 tests at different capacities. In the intervals between tests, the power unit will be disconnected from the power grid. The commercial launch of OL3 is now scheduled for 8 March 2023.  

In October, TVO discovered damage to the internals of the feedwater pumps located in the plant's turbine island during maintenance and inspection work. Ten days later, it said cracks of a few centimetres had been identified in all four of the feedwater pumps. Since then the schedule for restarting the plant has been deferred several times. The OL3 feedwater pumps are used to pump water from the feedwater tank into the steam generators. TVO has said the have no impact on nuclear safety.

TVO said, earlier in December that investigation work of the damage to the feed water pumps had mostly been completed. “The distortions of the pump impellers have probably been caused during test operation, where the pumps are run under exceptional conditions. Feed water pumps have been run in commissioning tests outside the normal operating areas, in which case the pumps would have been subjected to a higher load than usual,” TVO noted. “Re-breakage can be avoided by optimally driving the pumps and by using more durable impellers.”

TVO CEO Jarmo Tanhua said it was “very unfortunate” that the trial operation of Olkiluoto 3 was interrupted at the end of autumn when damage to the supply water pumps came to light. “This caused uncertainty about our winter season production for a long time. However, the investigations that turned out to be particularly challenging have now been completed so that, based on them, we can go back and do the final tests of the pilot operation and continue progressing towards regular electricity production.”

TVO said, on the basis of comprehensive investigations and the planned inspection programme for the pumps, “the trial operation of the plant unit can be temporarily continued with cracked feed water pumps in addition to the intact pumps of the current model”. Trial operation is continued with feed water pumps, two of which have a spare part impeller and two have a cracked impeller. Another pump with a cracked impeller works as a backup.

After the full power tests, power generation will be suspended for approximately four weeks for inspections of the feedwater pumps and restarting of the plant unit. The aim is to carry out the inspections in as close a schedule as possible, TVO said, noting that “there are still uncertainties regarding the duration of the production stoppage they require”. After this, before the start of regular electricity production, there is still a production period lasting about a month, during which Olkiluoto 3 produces electricity mainly at full power. 

“The new design-reinforced impellers are in production and are estimated to arrive at the turn of February-March 2023. Time has been reserved for the trial use programme both for checking the current running wheels and for changing new ones. Even during the trial operation phase, the plant unit produces approximately 15% of Finland's electricity needs at full power.”

OL3 attained first criticality on 21 December 2021 and was connected to the grid on 12 March. The 1600 MWe EPR was operated at full capacity for the first time in late-September. The Areva-Siemens consortium constructed the OL3 plant under a fixed-price turnkey contract. Construction began in 2005 various setbacks and delays mean the plant is now more than 10 years behind the original schedule and significantly over budget. Once regular electricity production has started, OL3 will produce about 14% of Finland's total electricity consumption.

Image: The Olkiluoto 3 EPR has started generating power in test mode (courtesy of TVO)