Olkiluoto 3 Commissioning Services

Olkiluoto 3 Nuclear Power Plant was commissioned for commercial use in spring 2023 which is important for the Nordic energy market as OL3 produces a steady baseload of 1600 MW of electricity thus reducing Finland’s dependency on electricity imports. Fortum’s nuclear experts were of significant help to TVO with the preparations and the commissioning between 2017 and 2023.

Teollisuuden Voima Oyj, the owner and operator of Olkiluoto NPP started the project for building a new EPR model nuclear power plant in 2005 and Fortum provided support  in multiple distinct projects for TVO throughout the lifecycle of OL3 project. From 2017 onwards, the detailed preparations for the start-up of the reactor became relevant and TVO ordered expert services from Fortum for supporting tasks relating to commissioning phase.

Nuclear commissioning services can be divided into two distinct parts:

  1. Consulting services for TVO before the actual commissioning: Fortum worked as a third party between the Plant Supplier and TVO in reviewing the core commissioning plans and procedures. Moreover, Fortum’s experts performed calculations of key safety parameters and simulated core commissioning tests with TVO’s codes in order to verify TVO’s models and to compare the results with Plant Supplier’s.
  2. Expert services during commissioning: In multiple subprojects, Fortum supported TVO’s organization with our own experts. For example, Fortum’s physicists worked as a part of TVO’s team during core commissioning while Fortum’s process engineers supported TVO with running the commissioning tests of the primary circuit.

During 2017-2022 Fortum reviewed Supplier’s core commissioning plans and procedures, run independent analyses on the core behavior during the commissioning tests, calculated key safety parameters, and worked with process analyses and modelling of the plant. In addition to the preparatory work, Fortum’s reactor physicists provided hands-on support to TVO during the actual commissioning of the reactor core, and Fortum’s experts were there when the first criticality was reached.

In addition to core commissioning expertise, Fortum also supported the testing and commissioning of different process systems in the power plant. For example, the commissioning tests for primary circuit of the power plant were completed with support of Fortum and got an official approval from the regulatory body. 


Fortum was able to integrate into the TVO organization quickly and smoothly thanks to highly skilled and flexible experts. Effortless integration could again ensure fluent operations and independent and self-guiding progress without need for constant supervision.

TVO successfully finished commissioning in 2023 and Olkiluoto 3 Unit started its commercial operation on April 16th 2023. With the electrical power output of 1600 MW, OL3 is projected to reduce Finland’s dependency on electricity imports drastically. In the OL3 project, Fortum demonstrated its capability of working with new reactor types, solving complex issues related to novel designs, and adaptability to customer needs.

Atte Moilanen

Project Manager
Newbuild and Operating Services
Tel: +358 50 313 3025
atte [dot] moilanen [at] fortum [dot] com

Nuclear Newbuild

Support for Nuclear Newbuild Projects

Decades of nuclear experience for supporting nuclear newbuild projects and newcomer countries throughout all phases of the project. Fortum offers technical support and consulting services which allow our Customers to have the know-how of an experienced Owner-Operator.

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