VTT studied the carbon footprint of nuclear district heating

Heating is also a major source of CO2 emissions, which is why the deep decarbonization of the energy system requires a wide range of alternatives to fossil heating fuels. To meet this challenge, VTT's spin-off company Steady Energy is developing the LDR-50 small modular reactor (SMR) for district heat production and low-temperature industrial applications. The technology aims for commercial use in the 2030s.

Nuclear energy is recognized as one of the low-carbon energy sources. The Intergovernmental Panel on Climate Change (IPCC), for example, puts the carbon footprint of nuclear electricity at the same level as wind power. However, comparisons including nuclear energy as one of the alternatives have not yet been made for the heating sector, where the energy production, distribution and consumption differ from electricity.

The VTT study evaluated the carbon footprint of heat produced using the LDR-50 reactor technology, together with other adverse environmental impacts over the life cycle of the production. Nuclear reactors do not produce flue gas emissions, and the environmental impacts consist of indirect contributions from the nuclear fuel cycle, as well as the construction, operation, maintenance and decommissioning of the heating plants.

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 to other commonly used district heating fuels, such as coal, natural gas and peat, as well as various biofuels. The emission number for the nuclear option was the lowest in the comparison. The difference was significant, especially compared to fossil fuels. Similar emissions for natural gas and hard coal, for example, were 282 gCO2/kWh and 515 gCO2/kWh, respectively.

In addition to combustible heating fuels, the specific emissions were compared to direct electric heating and heat pumps. The carbon footprint of these heating options is largely determined by the specific emissions of electricity consumed in the process. 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, Czechia 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. A broader comparison provides a better overall picture for ranking the different heating options against each other. This was considered important to avoid problem shifting, as adverse effects on land use or biodiversity, for example, are often overshadowed by small carbon footprint.

In none of the impact categories did nuclear-based district heating perform worse than the widely-used conventional heating fuels. 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.

Link to the publication: https://doi.org/10.3390/en17133250