Finnish technology company Steady Energy plans to build a pilot small modular reactor (SMR) plant in central Helsinki. The selected 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, valid until 2028. Construction is set to start in late 2025, with a budget of €15-20m ($17-23m) funded by capital investments already raised by Steady Energy.
The test facility will comprise a full-scale model of Steady Energy’s LDR-50 reactor module. Steady Energy was spun out of the VTT Technical Research Centre of Finland in 2023. The 50 MW LDR-50 is a simplified pressurised light water reactor specifically designed to operate at around 150°C and below 10 bar (145 psi). The reactor module comprises two nested pressure vessels, with their intermediate space partially filled with water.
When heat removal through the primary heat exchangers is compromised, water in the intermediate space begins to boil, forming an efficient passive heat transfer route into the reactor pool. The system does not rely on electricity or any mechanical moving parts, which could fail and prevent the cooling function. It was awarded a patent in 2021.
However, the pilot plant 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 power output. The 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.
This will be the first instance of physically testing a reactor module at full scale, beyond simulation environments, before 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,” said Steady Energy CEO Tommi Nyman. “Our objective is market-based small nuclear energy that can be built without subsidies.”
Antti Teräsvirta, Steady Energy’s project manager for the pilot facility, said the primary objective of the pilot facility “is to demonstrate that the core passive safety system of the LDR-50 functions effectively at full scale”.
Helen CEO Olli Sirkkanoted: “It’s fantastic that the pilot facility will be situated at Salmisaari, precisely where coal usage recently ceased. 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 ended coal usage in energy production earlier this spring with the closure of the Salmisaari coal power plant.
Helen, which launched the first phase of its nuclear programme in September 2024, aims to build either a combined heat and power plant or a district heating plant to achieve energy production in the 2030s. Helen is currently evaluating business models, mapping potential plant sites in the Helsinki metropolitan area and preparing to select a plant supplier.
