TOPICAL REPORTS Nuclear energy for heat applications Co-generating electricity and heat is a promising application the World Energy Council has noted, than 5 GW thermal (th) and they are operating by H. Barnert, energy supplies will have to increase in years in just a few countries, mostly in Canada and V. Krett ahead, especially in the electricity sector, to the USSR. and J. Kupitz meet the needs of the world's growing popula- There are many reasons for the disparity in tion. At the same time environmental problems, electricity and heat production from nuclear including the greenhouse effect linked to emis- energy. They include a fragmented co- sions of carbon dioxide and other gases from generation market, electrical grid sizes, low the burning of fossil fuels, pose serious costs of alternate energy sources for heat challenges in the view of the Intergovernmental production, and high costs of transportation and Panel on Climate Change and other bodies. distribution. Nuclear energy has the potential to con- For heat applications, specific temperature tribute to solutions of such problems. It already requirements vary greatly. (See graph on next has become a valuable energy source with page.) They range from low temperatures, just important environmental benefits. Its share of about room temperature, for applications such the world's electricity production is now about as hot water and steam for agro-industry, dis- 17%. trict heating, and sea water desalination, to up Yet only part of its potential is being real- to 1000° Celsius for process steam and heat for ized. The technology can play an even greater the chemical industry and high-pressure injec- role in assuring adequate energy supplies by tion steam for enhanced oil recovery, oil shale producing both electricity and heat for residen- and oil sand processing, oil refinery processes tial, industrial, and other purposes. and olefine production, and refinement of coal and lignite. The process of water splitting for the production of hydrogen is at the upper end. Up to about 550° Celsius, the heat can be Characteristics of energy use supplied by steam; above that, requirements must be served directly by process heat, since Worldwide, about 30% of total primary steam pressures become much higher than 550°. energy is used to produce electricity. Most of The upper limit of 1000° for nuclear-supplied the remaining 70 % is either used for transporta- process heat is set on the basis of the long-term tion or converted into hot water, steam, and strength capabilities of metallic reactor heat. This shows that the non-electrical market, materials. in particular that for hot water and steam, is Of course, there are industrial processes rather large. with temperature requirements above 1000°; for Nuclear energy is now being used to produce example, steel production. Such processes can electricity in more than 24 countries. Some utilize nuclear energy only via secondary 423 nuclear plants with a total capacity of about energy carriers, such as electricity, hydrogen, 324 gigawatts-electric (GWe) are operating and and synthesis gas. just over 80 plants with a total capacity of about 80 GWe are being built. Only a few of these plants are being used to supply hot water and steam. The total capacity of these plants is less Capabilities of reactors At all nuclear plants, the primary process in the reactor core is the conversion of nuclear energy into heat. Therefore, in principle, all Mr Barnert is with the Research Centre Juelich Gmbh, in Germany, and Messrs Krett and Kupitz are staff members nuclear reactors could be used to produce in the IAEA Division of Nuclear Power. process heat. However, in practice, two criteria IAEA BULLETIN, 1/1991 TOPICAL REPORTS In addition to the maximum temperature of Temperature the primary coolant, another important con- capabilities 1000 HTGR sideration is the temperature difference between of reactor types coolant inlet and outlet. The pressure of the produced steam is important when it comes to applications in the field of enhanced oil recovery: The deeper the oil resource, the higher the injection steam's pressure must be. Here, reactor types that have o AGR primary coolants other than water — the 6 LMFBR OCHWR, LMFBR, AGR, and HTGR - have 5 advantages. They easily can produce injection <3 500 steam with a higher pressure (for example, PWR J 10 MPa) for an oil field depth of about CD BWR QCHWR PHWR 500 metres. For water-cooled reactors, attain- LWGR ment of such pressures would require the addi- tional step of steam compression. PWR - Low pressure T Thermodynamics of electricity and heat Room 20 temperature generation As noted before, the primary conversion are decisive: the temperature of the produced process in a nuclear reactor is the conversion of heat (of primary coolant); and the pressure of nuclear energy into heat. produced steam (in some cases). This heat can be used in a "dedicated" mode Regarding the first factor, water-cooled of operation for direct heating purposes. In this reactors offer heat up to 300° Celsius. These case, no electricity is produced. types of reactors include pressurized-water The other mode is co-generation of heat and reactors (PWRs), boiling-water reactors electricity. Parallel co-generation is achieved by (BWRs), pressurized heavy-water reactors the extraction of some of the steam from the (PHWRs), and light-water-cooled, graphite- secondary side of the steam generator, before moderated reactors (LWGRs). Organic-cooled, the entrance to the turbine. Series co-generation heavy-water-moderated reactors (OCHWRs) is achieved by the extraction of some or all of reach temperatures of about 400°, while liquid- the steam at some time during steam expansion metal fast breeder reactors (LMFBRs) produce in the turbine when it has the right temperature heat up to 540°. Gas-cooled reactors reach even for the intended application. During this cycle, higher temperatures, about 650° for the ad- the extracted steam also has been used for elec- Temperature regions of heat vanced gas-cooled, graphite-moderated reactor tricity production. Series co-generation is consumption for (AGR), and 950° for the high-temperature gas- ideally suited to industrial processes related to typical industrial cooled, graphite-moderated reactor (HTGR). district heating, desalination, and agriculture. processes (See graph.) 1000 - Water-splitting for Examples of existing applications hydrogen production (R & D) Currently, a number of countries have Refinement of coal & lignite nuclear plants that are being used for the Reforming of natural gas production of hot water and steam. The total capacity amounts to less than 5 GWth. Oil refinery, define production Significant experience in the co-generation of electricity and heat has been gained in these *- Oil shale & oil sand processing countries, notably in the Soviet Union. This experience encompasses reactors at Beloyarsky, Kursk, Novovoronezh, Rovno, and Kol'skaya in *- Process steam, injection steam (HP) the Soviet Union; Tsinghua University in •> District heat, sea water desalination China; Bruce Nuclear Power Development in •- Agro-industry Canada; Bohunice in Czechoslovakia; Goesgen Room and Beznau in Switzerland; and Stade in temperature Germany. 22 IAEA BULLETIN, 1/1991 TOPICAL REPORTS A brief technical overview of some of these contributor to this effort has been the Shev- applications follows. chenko complex. It includes a fast breeder reac- Heat reactor in China. At the Institute of tor, type BN-350, three thermal power stations, Nuclear Energy Technology (INET), Tsinghua and a desalination plant with thermal distilla- University, Beijing, a nuclear heat reactor with tion equipment. The complex constitutes the the capacity of 5 MWth started operations dur- world's first, and for the time being the only, ing the winter of 1989-90. Used to supply heat demonstration plant where a nuclear reactor is to the INET centre, the reactor's operating used in desalination of sea water. experience has been very good. Its design prin- In the process, the BN-350's steam genera- ciples follow that of a PWR. The design pres- tors and a boiler unit supply steam to several sure of the primary circuit is 1.5 MPa (about different turbines. Steam from the BN-350 unit 10 times smaller than in a usual PWR) and tem- at 4.5 MPa and 450° Celsius is directed to the perature conditions in the primary loop are back-pressure turbines and to the condensing 186/146 degrees Celsius. Temperatures in the turbine. Steam from the back-pressure turbines intermediate loop are 160/110° at 1.7 MPa, and is directed towards the desalination units and the in the heat grid, 90/60°. industrial enterprises of the town. Parallel co-generation of process steam and The Shevchenko complex is the largest heat in Canada. One of the largest uses of centre of commercial thermal desalination in process steam occurs at the Bruce Nuclear the USSR. There are 12 operating desalination Power Development Facility in Ontario, units at the complex with a total capacity of Canada. The Candu PHWRs at this site are 140 000 cubic metres a day of distillate. capable of producing over 6000 MWe of elec; tricity as well as process steam and heat for use by Ontario Hydro and an adjacent industrial -Uranium Schematic of energy park. co-generation at Bohunice The Bruce-A nuclear station consists of four in Czechoslovakia 825-MWe units that are generating electricity. Additionally, the plants supply steam to a steam transformer plant. This plant generates 720 MWth of process heat and steam for heavy Electricity water production plants; 70 MWth for the Bruce energy centre; and 3 MWth for side services. The cycle is typical for parallel co- generation. Nuclear heat generated in the reac- tor is transferred to the steam generator via the primary heat transport loop.