Nuclear cogeneration in district heating systems: Optimal pathways to decarbonization

The decarbonization of the space-heating sector is a critical element in the global effort to transition to low-carbon energy systems. District heating (DH) systems are recognized as an effective way to combine low-carbon sources to provide heat for residential and tertiary sector buildings. As a proven technology for decarbonized electricity generation and with experience in coupling with DH networks, the use of nuclear plants in cogeneration mode to produce both heat and electricity appears to be a promising technology to contribute to the low-carbon mix for space heating. However, considering the substantial investment required for this technology and the availability of alternative low-carbon sources, such as biomass and large-scale heat pumps, the role of nuclear cogeneration in DH systems must be critically evaluated. This paper aims to identify key factors influencing the optimal transition pathways to low-carbon DH systems with the potential to include nuclear cogeneration plants. We seek to assess the cost-benefit analysis of nuclear cogeneration in a local context compared to alternative low-carbon heat production technologies. To do so, we develop a Generation Expansion Planning model (in the form of a Mixed Interger Linear Programming problem) to optimize the investment and dispatch of various heat sources from the perspective of a DH operator. This paper contributes to the literature on the use of nuclear cogeneration for district heating by conducting a comprehensive study of economic scenarios for multi-year optimal decarbonization of district heating networks, and includes heat transport aspects in the modeling and economic evaluation. Our results suggest that integrating a nuclear cogeneration plant (NCP) into the set of technologies available to the DH network brings significant system cost gains. These gains depend on the local configuration, with larger networks benefiting the most from the NCP availability. In most scenarios, investment is realized in some nuclear heat transport infrastructure, with the NCP providing the major part of the annual heat demand after 2050. Distance also influences these results, with NCPs bringing more economic benefit to the district heating network in the case of less distant installations. By studying the least-cost decarbonization pathways starting from different initial heat production mixes, we also show that the investment temporality, GHG emission trajectories as well as the system cost gains brought by the NCP integration are influenced in some way by the initial heat production capacities. Limits and uncertainties of this study are also discussed.