Finnish regulator publishes preliminary assessment of LDR-50 heat-producing modular reactor

Finnish nuclear regulator STUK has published the results of a joint preliminary assessment of Steady Energy’s LDR-50 small modular reactor concept. The Czech State Office for Nuclear Safety (SÚJB) also took part in the assessment. The regulators found no major safety barriers to further development of the design, but this is not a licensing decision.

In addition to Finland’s STUK, supervisory authorities from Sweden, Poland, the Czech Republic and Ukraine took part in the voluntary assessment. Each assessed the LDR-50 concept against its own national regulations and requirements, with the Czech side represented by the State Office for Nuclear Safety, supported by the State Institute for Radiation Protection.

This is not a permit or design approval

The joint assessment, known as the Joint Early Review, is primarily intended to enable regulators to exchange experience and make a preliminary check of whether the concept is broadly compatible with the requirements of their respective national frameworks. It is therefore not a step that replaces the standard permitting process or anticipates the outcome of future licensing.

The report also notes that the LDR-50 documentation reflects an early stage of technology development. Before any licensing process can begin, the design will need to be supplemented with more detailed safety analyses, technical justifications, emergency preparedness plans and an assessment of the design at the plant-wide level.

The LDR-50 is designed to supply heat to district heating networks

The report identifies the concept’s main strengths as its use of the defence-in-depth principle, inherent and passive safety features, and an effort to reduce the need for rapid operator intervention in certain accident conditions. Further work will need to focus on providing more detailed substantiation of the safety concept, addressing multi-unit configurations and shared systems, and demonstrating the reliability of selected safety functions.

The LDR-50 is a small modular reactor designed to produce heat, not electricity. Steady Energy gives the thermal output of one module as 50 MW. The unit is intended primarily for use in district heating systems, and potentially in low-temperature industrial applications. According to the company, it is designed to operate at lower temperatures and pressures than conventional power reactors.

Non-nuclear pilot facility under construction in Helsinki

Steady Energy has begun construction of a non-nuclear pilot facility in Helsinki, at the site of the decommissioned Salmisaari B coal-fired power plant. The facility is intended to be a full-scale mock-up of the LDR-50 reactor module, but it will not contain nuclear fuel. During testing, electric resistance heaters will provide the thermal output, simulating the operating behaviour of the future reactor.

The prototype is intended to verify the operation of the proposed systems and support the technology’s preparation for the next design and licensing phases. Steady Energy expects future commercial units could be located in underground facilities near existing district heating networks. This sets the LDR-50 apart significantly from conventional nuclear units and most power-generating SMRs currently in development.

Czech nuclear regulator also took part in the assessment

SÚJB’s involvement in the LDR-50 assessment builds on a broader effort by European regulators to share experience in assessing new types of nuclear facilities. The Czech authority has previously said the purpose of the cooperation is to gain experience, compare regulatory approaches and share expertise among regulators and their technical support organisations.

The significance of the assessment therefore extends beyond the Finnish project itself. For the participating regulators, it is also a practical opportunity to explore how one regulator’s preliminary assessment can be used as supporting material in other countries without undermining the independence of national permitting processes. The STUK report also notes that such cooperation requires clearly structured documentation, traceable conclusions and thorough preparation.

For Steady Energy, the outcome represents an important milestone in the further development of the technology. However, any permit for a specific facility will depend on a detailed safety case, the selected site and a decision by the relevant national regulator.