In Europe, the homes of 60 million people are currently kept warm during winter by 3500 local district heating networks, VTT notes. Heating is also a major source of CO2 emissions, which is why the deep decarbonisation of the energy system requires a wide range of alternatives to fossil fuels.
The VTT study evaluated the carbon footprint of heat produced using the LDR-50 small modular reactor (SMR) technology - being developed by VTT spin-off company Steady Energy for district heat production and low-temperature industrial applications - together with other adverse environmental impacts over the life cycle of the production.
The study relied on standard Life Cycle Analysis (LCA) methodology, which takes into account the energy and material streams of the different phases of the life cycle, together with the associated emissions. LDR-50 specific parameters were used as input data for evaluating the contributions from the fuel cycle. Since the technology is still under development, estimates for plant construction and the different stages of operation were based on conventional nuclear power plant technology.
The specific emissions for heat produced by the LDR-50 heating plant was estimated to be 2.4 grams of CO2 per kilowatt-hour. The result was compared with other commonly used district heating fuels, such as coal, natural gas and peat, as well as various biofuels. The emissions number for the nuclear option was the lowest in the comparison. The difference was significant, especially compared with fossil fuels. Similar emissions for natural gas and hard coal, for example, were 282 gCO2/kWh and 515 gCO2/kWh, respectively. For biofuels, the values ranged from 10 to 50 gCO2eq/kWh.
"More importantly, it was shown that the carbon footprint of nuclear-based district heating can be more than two orders of magnitude smaller than that of fossil heating fuels," VTT said. "The nuclear option also did well in comparison to direct electric heating and heat pumps, even when the electricity supply came from low-carbon sources."
The carbon footprint of these heating options is largely determined by the specific emissions of electricity consumed in the process, VTT noted. "To account for the variation in electricity sources, the average emission numbers from different European countries were included in the comparison. The carbon footprint of the nuclear option was comparable to heating with heat pumps in countries with a clean electricity mix, such as Sweden and France, and significantly lower when compared to grids with a large share of fossil production (e.g. Poland, Czech Republic and Germany)."
In addition to greenhouse gas emissions, the adverse environmental effects of nuclear district heating and conventional heating fuels were evaluated for 12 different impact categories, the study found.
"In none of the impact categories did nuclear-based district heating perform worse than the widely-used conventional heating fuels," it said. "In most categories the impact was clearly below the average. The result is largely explained by the very high energy content of uranium fuel. Even though uranium mining and milling inflicts negatively on the environment, the overall impact per produced amount of heat remains small compared to the alternatives."
VTT said the study shows that nuclear energy can become a viable option for replacing fossil fuels in heat production. It noted the largest emission reduction potential lies in countries where energy production still relies heavily on coal and natural gas, and district heating holds a large market share. Such countries include, for example, Estonia, Poland, Czech Republic, Slovakia, and Ukraine.
The LDR-50 district heating SMR - with a thermal output of 50 MW - has been under development at VTT since 2020. It is designed to operate at around 150°C and below 10 bar (145 psi). The LDR-50 reactor module is made of 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 company said. The system does not rely on electricity or any mechanical moving parts, which could fail and prevent the cooling function.
Steady Energy - which was spun out in May 2023 from the VTT Technical Research Centre of Finland - expects the construction of the first operational LDR-50 district heating plant to begin by 2028, with the first unit expected to be operational by 2030. The LDR-50 district heating SMR - with a thermal output of 50 MW - has been under development at VTT since 2020.
Last month, Steady Energy said it is set to start construction of its first LDR-50 district heating reactor pilot plant in Finland next year, with potential sites including the Finnish capital Helsinki and two other cities.
