Intensive year of supervision in Olkiluoto

The year 2022 was a significant year for the Olkiluoto 3 plant unit (OL3). STUK supervised the plant through inspection visits, monitoring commissioning tests and inspecting various reports and granted permits to proceed with commissioning power tests.


At the beginning of 2022, an interesting phase was reached in the OL3 commissioning tests, when after the first criticality, i.e. the start-up of the plant, the reactor power was raised in a controlled manner and, at the same time, it was tested that the plant functions as it should. The plant was tested for different kinds of disturbances, such as one in which the plant cannot be supplied with electricity from an external power network. In the test, the plant was disconnected from the national power grid and electricity was supplied to the plant's systems with its own backup systems. The test was successful. STUK monitored the most significant tests on site in Olkiluoto. With the help of the tests, a clear understanding was created that the plant operates safely and the operating organization (Teollisuuden Voima) controls the operations of the plant.
Some problems were also encountered. The purpose of the supervision of the commissioning phase is to also reveal any shortcomings and to ensure the safe and stable operation of the plant after the modifications. From STUK’s perspective, the biggest problems were not significant from the point of view of nuclear safety. The problems challenged the plant's ability to generate electricity rather than the meeting of the nuclear safety requirements. In these situations, STUK observed that the licensee has a good ability to solve the problems that arise. In addition, there were a few unexpected disturbances at the plant, but the plant operated safely regardless of the disturbances. After the corrective measures, the commissioning was continued. However, due to the challenges, the commissioning phase of the plant took longer than expected. The commissioning was completed in the spring of 2023 and the plant started regular electricity production.

All in all, the OL3 project required a lot of work from STUK. The project was officially started at STUK in 2003 and ended after the commissioning was completed in April 2023. Over the past twenty years, more than 100 STUK experts have participated in the project, and the total workload has been approximately 480 person-years. The project involved a tremendous amount of document processing, as more than 20,000 applications have been submitted to STUK during the project. In addition, STUK has carried out more than 10,000 on-site inspections and several thousand factory inspections around the world in approximately 30 different countries. Factory inspections were carried out, for example, in connection with the manufacture of components essential to the nuclear safety of OL3. STUK has also regularly exchanged information with authorities in other countries on the status, findings and lessons learned concerning OL3-type facilities. Through this comprehensive work, we have been able to ensure the safety of OL3 and its use.

Although the project phase for the OL3 supervision has now ended, the monitoring of the plant will continue throughout its service life, as ensuring safety is an ongoing activity.

Text: Essi Vanhanen, Project Manager of the OL3 Nuclear Commissioning regulatory control project