Finnish small modular reactor (SMR) developer Steady Energy will build a non-nuclear pilot facility at the decommissioned Salmisaari B coal power station in central Helsinki. The project aims to test and showcase the safety and maturity of the company’s LDR-50 reactor design for district heating.
Steady Energy has signed a lease agreement with energy firm Helen to use the old power plant building through 2028. The pilot facility will be built inside the existing turbine hall, with construction set to begin in late 2025. The project budget is estimated between EUR 15 million and EUR 20 million (USD 17–23 million), funded through investments already secured by Steady Energy.
The pilot plant will serve as a full-scale operational model of the LDR-50 reactor but will not use nuclear fuel. Instead, it will use electric heating elements to mimic the reactor’s heat production. The main goals are to test the reactor’s passive safety systems, evaluate its operation at full scale, and develop supply chains needed for future commercial reactors.
The LDR-50 design, which has been under development at Finland’s VTT Technical Research Center since 2020, is intended to supply 50 MW of thermal energy. It is designed to operate at about 150°C and under 10 bar pressure—conditions that are simpler and safer compared to conventional nuclear reactors. These features are meant to lower costs and make the technology viable for municipal utilities.
The reactor uses a unique passive safety system. It consists of two nested pressure vessels with water in the space between them. If the main cooling system fails, the water boils and removes heat without relying on electricity or moving parts.
Antti Teräsvirta, project manager at Steady Energy, said the pilot will be the first time the reactor module is tested physically at full scale. “The primary objective is to demonstrate that the core passive safety system of the LDR-50 functions effectively at full scale,” he said.
Helen CEO Olli Sirkka praised the project’s location and timing. “It’s symbolically significant that the reactor pilot is being built at Salmisaari, which just ended coal use,” he said. “We can now explore small-scale nuclear energy on our own site and also use the heat produced during testing to warm parts of Helsinki.”
Helen stopped using coal earlier this year, closing the Salmisaari plant and cutting Helsinki’s carbon emissions by 30%. The company aims for carbon neutrality by 2030 and fully combustion-free energy production by 2040.
Helen’s broader nuclear program, launched in September 2023, includes plans to build a combined heat and power plant or a district heating plant by the 2030s. The company is currently evaluating business models, identifying potential plant sites in the Helsinki area, and organizing a competitive bidding process for selecting a reactor supplier. The list of potential sites will be published in 2025, with a supplier to be chosen later.
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