Nuclear energy is competitive for urban district heating applications. According to the International Atomic Energy Agency, about 43 nuclear reactors around the world—mostly in Eastern Europe and Russia—provide district heating in addition to generating electricity. Combined heat and power arrangements are more attractive for new small- and medium-sized nuclear reactors because these designs incorporate enhanced safety features, require smaller investments, pose fewer financial risks, and may be easier to site closer to end-users.
Birdsill Holly designed the first financially successful district heating (DH) system in Lockport, New York, in 1877. His system, based on the delivery of steam, was widely imitated. By 1887, 20 district heating systems were in operation in the U.S.
Combined heat and power (CHP) was introduced as early as 1890. After these early attempts, wider introduction of the systems began in the beginning of the 20th century. The purpose was to rationalize ways of heating clusters of buildings from a central power plant or a boiler plant through a suitable distribution medium. In the U.S., the distribution medium was steam, while in Europe, the predominant distribution medium was hot water.
Within the past 30 years, district heating and cooling systems in the U.S. have expanded dramatically. A number of modern hot- and chilled-water district systems have been developed in cities across the country, including in St. Paul, Minnesota; Trenton, New Jersey; Jamestown, Buffalo, and Schenectady, New York; Indianapolis, Indiana; Springfield, Massachusetts; Hartford, Connecticut; and Manitowoc, Wisconsin. Meanwhile, old steam systems in New York City; Boston, Massachusetts; Philadelphia, Pennsylvania; Baltimore, Maryland; St. Louis, Missouri; Youngstown and Dayton, Ohio; and Rochester, New York, have been renovated and/or expanded. For all these systems, fossil fuel is the present energy source. However, extension of these and other systems offers the possibility of loads commensurate with the capabilities of modern nuclear energy sources.
Current Operational Status of Nuclear-Based District Heating Systems
Nuclear-based district heating appears promising for urban areas plagued with polluted air and greenhouse gases released from burning of fossil fuels. Advantages of nuclear heat supply are fuel conservation, improvement of the environment, and reduction of heat discharged to the atmosphere. Almost two-thirds of the heat generated in a conventional nuclear power plant is released to the environment. A well-designed CHP system could boost a nuclear plant’s energy efficiency from about 33% to 80%. Nuclear heat in the form of hot water can be economically delivered up to 100 miles away at competitive cost and with a heat loss of 2% to 3%.
When a nuclear district heating system replaces individual heating boilers, the combustion process emissions from thousands of small stacks are eliminated. Nuclear energy can be competitive for urban district heating applications (Figure 1). Therefore, it is justified to review the status of recent nuclear-based district heating technology.
1. Typical nuclear-based district heating systems extract heat from the reactor plant’s secondary circuit. Hot water obtained in the process can be supplied to district heating systems as far away as 100 kilometers from the plant. Courtesy: Joseph Technology Corp.
U.S. According to a recent estimate by the U.S. Energy Information Administration, there are more than 660 district energy systems operating in the U.S. with installations in every state. However, the list of large hot water–based district heating systems feasible for nuclear DH supply is limited.
An extensive study was conducted in Connecticut, which focused on using waste heat from an existing nuclear power plant. It found substantial benefits from using nuclear heat, but concluded that the realization of maximum economic and social benefits would require current laws, practices, and regulations to be modified. It suggested the larger energy perspective would have to be considered including desegregating the treatment of energy, and incorporating land use planning and associated economic development into the process.
Next-generation nuclear plant development in the U.S. includes a modular prismatic high-temperature gas-cooled reactor (HTGR) having unit thermal ratings up to 625 MWth, with various configurations of heat transport systems that provide steam and/or high-temperature fluids. The range of power ratings, temperatures, and heat transport system configurations provides flexibility in adapting the modules to specific applications, including CHP. The development project for the reactor was authorized by the Energy Policy Act of 2005. The project is managed by the Idaho National Laboratory with funding through the Department of Energy. The Next Generation Nuclear Plant (NGNP) Industry Alliance was created in 2010 to promote the development and commercialization of this HTGR.
Russia. District heating accounts for more than 70% of all heat consumed in Russia for space heating and domestic hot water. Many operating Russian nuclear power plants use non-controlled steam extraction for district heat supply (Table 1).
Table 1. List of Russian nuclear combined heat and power plants. Source: Joseph Technology Corp.
By the end of 2019, Unit 1 of Russia’s Leningrad II nuclear power plant (Figure 2) was connected to the district heating system of the city of Sosnoviy Bor (population 65,000). The station is equipped with a new VVER-1200 reactor that provides electricity and heating lost with the closure of the first of four early-1970s vintage RBMK-1000 units at the nearby Leningrad power plant.
2. The Leningrad II nuclear power plant in northwest Russia. Courtesy: RIA Novosti archive, image #305005 / Alexey Danichev / CC-BY-SA 3.0
A number of Russian cities have expressed an interest in using small nuclear reactors to supply heat and power. A feasibility study undertaken by ROSATOM, Russia’s State Atomic Energy Corp., concluded that up to 38 CHP reactors could potentially be deployed at 14 sites for this purpose. The Dollezhal Research and Development Institute of Power Engineering (NIKIET) has completed the detailed design of the VK-300 boiling water reactor with 750 MW thermal capacity and 150 MW to 250 MW electric, depending on the required mix of heat and power. It uses proven components, including similar fuel elements to the large established VVER pressurized water design. VK-300 features passive cooling and safety features, and has no need for operator action in an emergency, or for offsite electricity or water supply. The VK-300 has two containments, and the consequences of any accident should not extend beyond the site boundary. The next step would be to set up a program to implement a pilot plant.
In May 2020, the Akademik Lomonosov, the world’s first commercial floating nuclear combined heat and power plant (Figure 3), began supplying 70 MW of space heating and domestic hot water to the Russian port of Pevek on the East Siberian Sea. The plant is equipped with KLT-40S reactors, variants of the KLT-40 designs that were developed to power icebreakers.
3. The floating power unit Akademik Lomonosov was connected to the power grid and began generating electricity for the first time in the isolated Chaun-Bilibino network in Pevek, Chukotka, Russia’s Far East, in December 2019. Several months later, the plant also began supplying Pevek’s heat networks. Courtesy: Rosatom
China. China’s district heating network is one of the world’s largest, but it is also a major source of air pollution from coal firing in many Chinese cities. China is substantially growing its district heating market, supplying close to 55% of demand in north China. China recently started up its first commercial nuclear-based CHP system, using two newly operational AP1000 reactors at the Haiyang nuclear power plant (Figure 4) to heat seven million square feet of housing in Haiyang, a coastal city with a population of about 658,000 in Shandong province. A later stage modification is planned to the units, which could expand the heating capacity to 200 million square feet of housing with a heating radius of about 60 miles.
4. Haiyang’s nuclear district heating project feeds non-radioactive steam from the secondary circuit of both AP1000 units through an onsite multi-stage heat exchanger contained in the building shown here, before going offsite to a heat exchange station run by a local thermal company. Courtesy: State Power Investment Corp.
China is also constructing a commercial high-temperature reactor power module (HTR-PM) plant consisting of twin 250-MWth reactor units. While initially being used to demonstrate steam turbine power generation, the reactor technology—with an outlet temperature of 1,382F—has a longer-term objective for industrial heat applications, including process steam and hydrogen production. The Institute of Nuclear and New Energy Technology of Tsinghua University in Beijing is developing a thermochemical iodine-sulfur process and high-temperature steam electrolysis (HTSE). Researchers recently successfully ran continuous hydrogen production tests for both processes. The hydrogen technologies are intended for future use with the HTR-PM. Furthermore, China is looking to export the HTR-PM technology, having, since 2016, signed a series of agreements with Saudi Arabia to cooperate in deploying desalination cogeneration technology in that country.
Switzerland. For many years, the Beznau nuclear CHP plant (2 x 365 MWe) has successfully supplied district heating in addition to power. Beznau supplies 80 MWth of heat to homes and industry over an 80-mile network serving 11 towns.
Since December 1979, Gösgen, a 1,010 MWe pressurized water reactor (PWR), has been extracting process steam and feeding it to a cardboard factory and other nearby heat consumers. In the turbine building, about 1% of the steam is diverted from the live steam system to heat a water/steam circuit that runs through a one-mile-long steam line to the cardboard factory. The line has a maximum capacity of 150,000 lb/hr of steam, operating at a pressure of 170 psi and a temperature higher than 400F. The quantity of heat transferred is equivalent to about 45 MWth. In 1996, the system was extended by a small district heating network in nearby municipalities. In 2009, a separate water/steam circuit was built for another paper factory.
Finland. Finland has an extensive modern hot water district heating infrastructure. The Helsinki district heating system started operations in 1953, and today district heating covers more than 93% of the city heating energy demand. The system is applicable for nuclear CHP supply.
In February 2020, VTT Technical Research Centre in Finland announced the launch of a project to develop a small modular reactor for district heating. Most of the country’s district heating is currently produced by burning coal, natural gas, wood fuels, and peat, but it aims to phase out its use of coal in energy production by 2029.
France. An extensive study focusing on the use of nuclear CHP for the large district heating system in Paris was performed in France. The study recommended the initial district heating development steps.
South Korea. In the last 30 years, South Korea has developed large modern hot water district heating systems in many cities. The large district heating system in the capital Seoul could be suitable for nuclear heat supply.
The Korea Atomic Energy Research Institute (KAERI) began developing a 330-MWth integral-type small reactor, cleverly named SMART (System-integrated Modular Advanced Reactor), in 1997. SMART has integral steam generators and advanced passive safety features. It is designed for generating electricity (up to 100 MWe) and/or thermal applications such as district heating and seawater desalination. U.S.-based engineering company URS provided technical services to KAERI. The reactor design received standard design approval from Korea’s regulatory body in 2012, and KAERI incorporated post-Fukushima modifications into the design in 2016, making cooling fully passive.
The cost is expected to be about $5,000/kWe. It has 57 fuel assemblies that are very similar to typical PWR designs, but shorter, and it operates with a 36-month fuel cycle. In March 2015, KAERI signed an agreement with Saudi Arabia’s King Abdullah City for Atomic and Renewable Energy to assess the potential for building at least two SMART reactors in the country. In January 2020, a revised pre-project engineering contract was signed, allowing Korea Hydro and Nuclear Power (KHNP) to participate in the Saudi Arabian project. KHNP will lead efforts to refine the reactor design, license its use for deployment in Saudi Arabia, and develop business models and infrastructure, as well as promote the export of the technology to other countries.
Nuclear CHP Project Challenges
Issues to be resolved relative to the use of heat supplied by nuclear energy include public acceptance of nuclear plant sites in relative proximity to populated centers, development of economical heat transport methods, and availability of large dual-purpose turbines for production of electricity and extraction steam at suitable temperatures and pressures. In the U.S., future use of district heating supplied from nuclear CHP will require increased commitments to district heating and greater acceptance of nuclear plants sited relatively close to cities to limit transmission costs.
Although costs and technology status of nuclear-based district heating are favorable and there are environmental advantages, institutional barriers are deterrents to implementation. These barriers must be overcome before the energy conservation potential of this approach can be realized on a significant scale.
—Ishai Oliker, PhD, PE ([email protected]) is principal with Joseph Technology Corp. He has been involved in power plant development and design in the former USSR, Korea, China, and the U.S. for more than 30 years.