Nuclear-powered district heating nears commercialization in Finland

Finland’s plan to power much of its district heating systems with nuclear is moving forward via a VTT spin-off company that aims to build and commercialize a reactor-based heating plant by the end of the decade.

Global district heating or cooling systems, whereby a single power-generating source warms or cools a residential, commercial, or industrial area, are found predominantly in China, Russia, and parts of Europe.

When the power-generating source is from fossil fuels, which a large majority are, greenhouse gas emissions are high.  

Existing district heating systems accounted for about 3.5% of global CO2 emissions in 2021 and emissions from the  systems are steadily rising, up 3.5% in 2021 from just a year earlier and up 15% from 2010, says the International Energy Agency (IEA).

They are also heavy electricity users.  

In 2018, district heating in the European Union - mostly in Germany and Finland - consumed around 445 TWh, 12% of the final energy consumption for space heating and hot water, just over half of which was for the residential sector.

District cooling, meanwhile, consumed 3.1 TWh and was mostly for the service sector, according to one European Commission (EC) study.

In Europe, two thirds of district heating supply is generated using fossil fuels with low-carbon fuels – biomass, biofuels, and renewable waste – making up 25%, according to the EC’s ‘District heating and cooling in the European Union: overview of markets and regulatory frameworks under the revised Renewable Energy Directive.’

There are around 3,500 district heating networks throughout Europe serving some 60 million people, according to Steady Energy, which was established for the purpose of commercializing the reactor developed by VTT Technical Research Centre of Finland, the LDR-50.

Global annual heat deliveries to end-use sectors through district heating networks, 2000-2021

(Click to enlarge)

Source: International Energy Agency

Purpose-built reactor

The LDR-50 district heating reactor, the first of its kind, will have a heat output of 50 MW and is designed to operate at low temperatures and low pressures.

While electricity generation requires a turbine cycle and high-pressure steam heated to around 300°C, district heating networks operate at much lower temperatures, with maximums of around 120°C.

Developing a heat-only reactor allows lowering the temperature, and more importantly, the pressure, says Research Professor for Reactor Safety at VTT Jaakko Leppänen.

“The operating pressure of LDR-50 is closer to a household espresso machine than a conventional pressurized water reactor. This simplifies the manufacturing of reactor components and design of passive safety systems,” Leppänen says.

Development of the LDR-50 district heating reactors was started by VTT Technical Research Centre in February 2020.

By the end of June 2023, Steady Energy announced it had raised some 2 million euros ($2.2 million) in seed funding and will use the cash to build a 1:1 scale mockup of the plant powered by electric heat to demonstrate its functionality.

VTT will continue basic design and computational analysis work as Steady Energy constructs the test facility.

Once the experimental program has been completed, the Steady Energy will conduct engineering and detailed design of the LDR technology with VTT as its technical support organization, CEO of Steady Energy Tommi Nyman says.

The first investment decision on a plant is likely to be made by a Finnish company, though a decision is yet to be made, Nyman says.

“There are several energy companies in Finland who have shown interest. The first plant will be designed according to needs of the customer, and a minimum size is one reactor which delivers a maximum of 50 MW of thermal power,” Nyman says.

As a district heating reactor, the most relevant market area for the LDR-50 is in northern and eastern Europe in countries such as the Baltics, Poland, Czech Republic, and Ukraine, he says.

However, the reactor could also be marketed further afield for other applications.

“LDR delivered as process steam plants and as desalination plants have market opportunities globally,” he says.

Challenges remain

The LDR-50’s conventional technical design, which does not rely on pumps for primary coolant flow or emergency cooling, complicates computational modeling, according to VTT's Leppänen.

“We have very good tools for simulating the reactor behavior, backed up CFD (computational fluid dynamics) simulations, but eventually the safety demonstration will require large-scale thermal hydraulic experiments,” he says.

“Setting up the experimental program will be a major task and challenge for the project, especially considering the tight schedule.”

The transition of existing district heating and cooling systems from fossil fuels to nuclear also carries its own potential speed bumps due to the actual, and perceived, risks that exist within nuclear reactors.

It is uneconomical to transport heat over long distances, so district heating systems are traditionally found within a short distance of urban areas covered by the network.

This may not be possible for a nuclear reactor due to restrictions imposed by emergency planning zones, which are minimum distances around a plant that range from 3-5 km for Precautionary Action Zones (PAZs) to 100-300 km for ingestion and commodities planning distances (ICPD), according to International Atomic Energy Agency (IAEA) guidelines.

“Similar concepts cannot be applied to a district heating reactor, so we’ll have to demonstrate that even in the worst kind of accident, the consequences will be limited within the boundaries of the site,” Leppänen says.

Passive safety functions and the small size of the unit – which is comparable with research reactors operating on university campuses – mean the LDR-50 may not face such stringent boundary restrictions.

“In general, nuclear safety is based on the so-called defense-in-depth principle, and since we cannot take advantage of large emergency planning zones, more effort has to be devoted to inner defense barriers to reach the same level of overall safety,” he says.

Acceptance of nuclear power and nuclear-based district heating in Finland is high, but NIMBYism (Not in my backyard) is likely to rise its head if anyone attempts to put a nuclear reactor directly within communities.

Inner city land values are also likely to be a factor, and the system will probably be located in industrial settings outside of residential areas.

“The only way to maintain this good public perception is to be open and transparent about the technology that we are developing and also about the risks … If we want to reduce these emergency planning zones, we simply have to put more effort on the inner barriers. We believe this is doable,” Leppänen says.

By Paul Day