Finland’s Teollisuuden Voima (TVO) said the EPR reactor at unit 3 of the Olkiluoto NPP (OL3) had restarted trial operation, with regular electricity production expected to begin on 17 April. The previous date given for this in February was 29 March.

In autumn 2022, cracks were identified in the impellers of the feedwater pumps located in OL3’s turbine island. Tests at full power were continued after extensive investigations with two cracked impellers and two spare impellers. The observations made during the feedwater pumps’ inspections were in accordance with the calculations and analyses performed earlier. To avoid the recurrence of similar damage, impellers with more robust measurements were designed for OL3. New impellers were installed in all four of OL3’s feedwater pumps during a scheduled outage and the plant supplier carried out inspections in preparation for resumed trial operation. The reactor was briefly back in test mode in late December and early January before being closed again for maintenance.

OL3 attained first criticality in December 2021 and was connected to the grid on in March 2022. 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 and 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 starts, OL3 will produce about 14% of Finland's total electricity consumption.

TVO said maintenance of the valve stations of the pressuriser has now been completed allowing commissioning to continue. A 24-hour performance test will be followed by a week of tests to ensure reliability and uninterrupted, continuous production capability. During a demonstration run lasting around a month, the power will be briefly reduced to several different power levels before regular production begins in April.

Image: Olkiluoto 3 EPR (courtesy of TVO)