Finnish power company Fortum and technology company Steady Energy have signed a framework agreement under which Fortum will support development of Steady Energy’s small modular reactor (SMR) for district heating. Fortum will provide a wide range of nuclear expert services to support design of the operation and maintenance concept as well as the development of the functions related to the plant’s operation.
The agreement could enable Fortum to provide the operation and maintenance services required by Steady Energy’s SMRs in Finland and Sweden in the future. In addition, Fortum will finance the development of Steady Energy’s LDR-50 district heating reactor with an equity investment of €2.1m ($2.4m). This is part of Fortum’s Innovation & Venturing activities, through which Fortum aims to identify and support startups and technologies that promote a lower-emission future.
Finland’s Steady Energy is a startup company spun out from the VTT Technical Research Centre of Finland in 2023 to provide engineering services to develop Steady Energy’s LDR-50 SMR. The LDR-50 district heating SMR has been under development at VTT since 2020.
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. 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. The LDR-50, the size of a standard shipping container, is designed to be built underground for added safety and to free valuable real estate for key urban areas. It is optimised for district heating, industrial steam production, and desalination projects.
In June 2025, the Finnish Radiation & Nuclear Safety Authority (STUK – Säteilyturvakeskus) completed an assessment of the concept of Steady Energy’s LDR-50 NPP. STUK found that “nuclear and radiation safety, security arrangements, emergency arrangements and nuclear material safeguards solutions are such that they can be designed to meet safety requirements”.
“Our goal is to complete the design phase by 2028, enabling us to begin the construction of the first commercial plant. The current policy environment is very favourable towards SMR development in Finland. A revised nuclear energy act is expected to be adopted by the parliament later this year with one specific aim to accommodate the adoption of SMRs,” said Steady CEO Tommi Nyman.
Anni Jaarinen, Vice President, Nuclear Services at Fortum, noted: “At Fortum, we have almost 50 years of experience in owning and operating a nuclear power plant safely and with good results. We have invested in the development of operation and maintenance and the efficiency of our own operations for a long time. It is very interesting to now work with Steady Energy to develop an optimal operation and maintenance concept for their new type of district heating reactor.”
Fortum has already participated in the development of Steady Energy’s LDR-50 district heating reactor by offering its process design and simulation expertise in reactor modelling as an expert service. In March 2025, Fortum agreed to support the development of Steady Energy’s district heating reactor with its simulation expertise. The goal was to create a comprehensive digital twin for the LDR-50 using Apros software developed jointly by Fortum and VTT.
“Small nuclear power is being developed as an alternative to replace fossil fuels in energy production. Finland has strong and extensive expertise in nuclear power, and Steady Energy is leveraging that foundation to create a new, low-emission district heating solution,” says Gustav Eilertsen, Vice President, Innovation & Venturing.
Steady Energy has already signed agreements for 15 reactors in Finland and is working on three projects in Helsinki, Kuopio and Kerava. The aim is for construction of the first plant – to be the clean energy source for a district heating scheme – to begin in 2029.
