May 6, 2025

Steady Energy to build small nuclear pilot plant inside a former coal plant in central Helsinki

Finnish technology company Steady Energy will build a small nuclear reactor (SMR) plant pilot facility in central Helsinki, located at the decommissioned Salmisaari coal power station. The pilot plant will demonstrate the maturity and safety of Steady Energy’s small modular reactor (SMR) technology.


Espoo – Finnish SMR developer Steady Energy Ltd will begin construction of its test facility in central Helsinki. The chosen site is the turbine hall of the Salmisaari B coal power plant, owned by energy company Helen Ltd. Steady Energy and Helen have signed a lease agreement for the site, running until 2028. Construction is set to start in late 2025, with a budget of €15 to €20 million, funded by capital investments already raised by Steady Energy.

The test facility equipment is a full-size model of the LDR-50 reactor module. However, the pilot plant differs from the actual LDR-50 unit in several ways - for example, it will not contain nuclear fuel in its reactor core. Instead, water within the reactor loop will be heated by electrical resistance elements providing approximately one-tenth of the LDR-50 reactor’s actual power output. Steady Energy’s facility will fit entirely within the turbine hall and will not affect the external appearance of the building. Commercial reactors will eventually be built underground, similarly leaving the cityscape largely unaffected.

This will be the first instance of physically testing a reactor module at full scale, beyond simulation environments, before actual construction. “We minimise cost and time risks by testing the plant thoroughly before selling it. Private investors see this approach as a major reason to trust us,” says Tommi Nyman, CEO of Steady Energy. “Our objective is market-based small nuclear energy that can be built without subsidies,” Nyman adds.


“The primary objective of the pilot facility is to demonstrate that the main passive safety system of the LDR-50 functions effectively at full scale,” says Antti Teräsvirta, Steady Energy’s project manager for the pilot facility. “It’s fantastic that the pilot facility will be situated at Salmisaari, precisely where coal usage recently ceased,” comments Olli Sirkka, CEO of Helen Ltd. “As landlords, we can closely follow the facility’s development and, as a bonus, gain about six megawatts of additional emission-free capacity to our grid.”


Helen Ltd ended coal usage in energy production earlier this spring with the closure of the Salmisaari coal power plant, reducing Helsinki’s carbon emissions by approximately 30 percent. The company aims to achieve carbon neutrality by 2030 and entirely combustion-free energy production by 2040.

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