The reactor of Olkiluoto's third nuclear power plant unit (OL3) was started by Teollisuuden Voima Oyj (TVO) on 21 December 2021 and has since continued the commissioning in stages.

The Radiation and Nuclear Safety Authority (STUK) supervises the commissioning and TVO needs its permission before increasing the power of the reactor to the next stage of commissioning. The previous STUK’s authorization concerned the increase of the reactor power from 5% to 30%.

The OL3 plant provider and TVO have ensured that the plant functions as planned and tested the plant behaviour during operational occurrences. STUK has reviewed the plans and instructions of the tests and supervised the most significant tests on site. STUK has also reviewed the most significant test results. The commissioning tests have shown that the plant is operating as planned and that it is safe to increase the plant's power above 30% of the full capacity.

Next, TVO will need an authorization granted by STUK to the OL3 unit when the commissioning tests are to be carried out at more than 60% of power.

OL3 produced electricity for the Finnish grid for the first time in March, when the power of the reactor was 25% of the full capacity. According to the plan provided by TVO, the plant’s regular electricity production will start in July 2022.