Nuclear microreactors are an untapped opportunity for clean and resilient district energy production at universities, hospitals, airports, government facilities, urban networks, and more. The Electric Power Research Institute (EPRI) is accelerating the use of nuclear energy to decarbonize district energy systems by identifying and solving the biggest remaining challenges.

District energy systems centralize thermal energy production to achieve cost savings and reliability benefits for multiple buildings. Historically used for heating, today’s district energy systems are increasingly being developed for cooling and cogeneration of electricity. This approach increases energy independence and efficiency at universities, hospitals, airports, government facilities, and urban districts.

Behind the scenes, 170 kilometers of piping trace a hidden grid beneath Manhattan, where ConEdison’s Steam Business Unit serves 1,800 customer buildings and currently stands as the largest district steam system globally. According to the International District Energy Association (IDEA), there are at least 660 district energy systems in the US, and the International Energy Agency (IEA) notes that in some countries like Denmark and Sweden, district systems already provide the majority of the national heat supply.

According to IEA, district heating accounted for 16 EJ (1.6 x 1019 joules) in 2021 or some 8% of global heat energy, and the market continues to grow. District energy is significantly more space- and energy-efficient than isolated generation, and is also more resilient against outages, attacks, and extreme weather. As the global population continues to urbanize, district energy systems will only become more widespread.

Compared to isolated heating, cooling, and electricity generation, district energy systems simplify building operations and free up valuable floor space. These systems benefit from economies of scale, avoiding capital costs for boilers, chillers, and generators, and the larger the network, the greater the savings. They also reduce labour, repair, and maintenance expenses, and district energy system owner-operators may be eligible to receive tax benefits and rebates from reduced carbon emissions and classification as a utility.

The need for carbon-free district energy

Despite the benefits of district energy, one main problem remains: district energy is conventionally generated from carbon-intensive sources, with nearly 90% of district heat produced from fossil fuels, according to the IEA. While renewables have notably achieved significant penetration into some markets in Europe, carbon-free sources still represent less than 8% of district heat supply globally.

IEA estimates that reaching net-zero emissions by 2050 will require connecting 350 million buildings to district energy networks by 2030, accounting for 20% of the world’s heating. With this extensive growth, we’ve identified the need for new, efficient generation sources for district energy. Recent developments in a new generation of advanced nuclear reactor designs could help meet this energy need.

Compared to the gigawatt-scale reactors of the 20th century, advanced nuclear reactors being designed and developed today come in a wider range of shapes and sizes, including small and versatile microreactors. Microreactors can deliver up to 60 MWth of power and can be used for cogeneration of heat, cooling, and electricity. Microreactors could be used to upgrade retiring fossil-fuel based generation in existing district energy systems, or they could be integrated directly into newly built systems.

Nuclear microreactors are carbon-free and can operate on very small land footprints. By integrating nuclear technology into district energy systems, we can address the challenges of carbon-intensive energy sources while improving reliability and resilience. Although large-scale nuclear reactors have been used in district heating systems before, microreactors have much greater potential for decarbonizing district energy systems in the next ten years due to their cogeneration versatility and small size.

In particular, High-Temperature Gas Reactors (HTGRs) and liquid metal-cooled reactors are currently the most considered microreactor designs. HTGRs use trisostructural isotropic (TRISO) fuel pellets that safely hold all radioactive material within, and an inert helium coolant with outlet temperatures that can exceed 700°C, achieving the high temperatures necessary for efficient cogeneration. Liquid metal-cooled reactors are designed to use liquid lead or sodium, which enables highly efficient transfer of heat. Safety is always paramount in the nuclear industry, especially in urban areas, and nuclear microreactors incorporate passive cooling and inherent safety mechanisms to ensure safe operation without external power in the event of emergencies.

Nuclear’s NuIDEA for District Energy

EPRI is spearheading the Nuclear in District Applications (NuIDEA) initiative to pave the way for nuclear microreactors to decarbonize district energy systems as the technology becomes available. NuIDEA provides technical guidance, fosters collaboration, and proactively solves challenges to help our members implement nuclear for district energy uses.

NuIDEA’s mission is to enable nuclear energy as an option for the district energy market by 2026. This initiative is meant to iron out the largest remaining hurdles, such as those pertaining to technology, policy, and financing so that the district energy market can begin to consider using carbon-free nuclear energy as an alternative to fossil fuels and renewables within the next few years.

NuIDEA is a collaborative effort led by EPRI, with over 25 members that are interested in developing nuclear energy as a viable option for district systems. Earlier this year, the NuIDEA Action Plan was released, which laid out the direction and goals for the initiative’s research over the next few years. Based on the Action Plan, NuIDEA members will work to develop solutions for policy, public awareness, ownership models, financing, insurance, project development and execution, technology, regulation, permits, operations and maintenance, and security.

NuIDEA primarily benefits district energy owner-operators and supporting organizations who are interested in exploring nuclear energy as an option for district applications. This work will provide the industry with practical approaches to utilizing nuclear energy in district energy applications. The key focus point for NuIDEA’s research is to help owner-operators succeed at implementing nuclear energy in district systems.

Author: Jeremy Shook, EPRI Principal Project Manager