- Steam generator (nuclear power)
:"This is an article about nuclear power plant equipment. For other uses, see
steam generator ."Steam generators areheat exchanger s used to convert water intosteam from heat produced in anuclear reactor core . They are used inpressurized water reactor s between the primary and secondarycoolant loops.In commercial power plants steam generators can measure up to 70 feet in height and weigh as much as 800 tons. Each steam generator can contain anywhere from 3,000 to 16,000 tubes, each about three-quarters of an inch in diameter. The coolant is pumped, at high pressure to prevent boiling, from the reactor coolant pump, through the
nuclear reactor core , and through the tube side of the steam generators before returning to the pump. This is referred to as the primary loop. That water flowing through the steam generator boils water on the shell side to produce steam in the secondary loop that is delivered to theturbine s to makeelectricity . The steam is subsequently condensed via cooled water from the tertiary loop and returned to the steam generator to be heated once again. The tertiary cooling water may be recirculated tocooling tower s where it sheds waste heat before returning to condense more steam. Once through tertiary cooling may otherwise be provided by a river, lake, ocean. This primary, secondary, tertiary cooling scheme is the most common way to extract usable energy from a controlled nuclear reaction.These loops also have an important safety role because they constitute one of the primary barriers between the radioactive and non-radioactive sides of the plant as the primary coolant becomes radioactive from its exposure to the core. For this reason, the integrity of the tubing is essential in minimizing the leakage of water between the two sides of the plant. There is the potential that if a tube bursts while a plant is operating; contaminated steam could escape directly to the secondary cooling loop. Thus during scheduled maintenance outages or shutdowns, some or all of the steam generator tubes are inspected by
eddy-current testing .In other types of reactors, such as the
pressurised heavy water reactor s of theCANDU design, the primary fluid isheavy water .Liquid metal cooled reactor s such as the inRussia nBN-600 reactor also use heat exchangers between primary metal coolant and at the secondary water coolant.Boiling water reactor s do not use steam generators, as steam is produced in thepressure vessel .Types
Westinghouse and
Combustion Engineering designs have vertical U-tubes with inverted tubes for the primary water.Canadian ,Japan ese, French, and German PWR suppliers use the vertical configuration as well. Russian VVER reactor designs use horizontal steam generators, which have the tubes mounted horizontally.Babcock and Wilcox plants (e.g.,Three Mile Island ) have smaller steam generators that force water through the top of the OTSGs (once-through steam generators; counter-flow to the feedwater) and out the bottom to be recirculated by the reactor coolant pumps. The horizontal design has proven to be less susceptible to degradation than the vertical U-tube design.Tube material
Various high-performance alloys and
superalloys have been used for steam generator tubing, including type 316stainless steel , Alloy 400,Alloy 600 MA (mill annealed), Alloy 600TT (thermally treated), Alloy 690TT, and Alloy 800Mod.See also
*
Nuclear power plant
*Power station
*Steam shower
*Steam turbine
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