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Nuclear marine propulsion
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Nuclear marine propulsion
Nuclear marine propulsion is propulsion of a ship or submarine with heat provided by a nuclear reactor. The power plant heats water to produce steam for a turbine used to turn the ship's propeller through a gearbox or through an electric generator and motor. Nuclear propulsion is used primarily within naval warships such as nuclear submarines and supercarriers. A small number of experimental civil nuclear ships have been built.
Compared to oil- or coal-fuelled ships, nuclear propulsion offers the advantage of very long intervals of operation before refueling. All the fuel is contained within the nuclear reactor, so no cargo or supplies space is taken up by fuel, nor is space taken up by exhaust stacks or combustion air intakes. The low fuel cost is offset by high operating costs and investment in infrastructure, however, so nearly all nuclear-powered vessels are military.
Most naval nuclear reactors are of the pressurized water type, with the exception of a few[quantify] attempts[by whom?] at using liquid sodium-cooled reactors. A primary water circuit transfers heat generated from nuclear fission in the fuel to a steam generator; this water is kept under pressure so it does not boil. This circuit operates at a temperature of around 250 to 300 °C (482 to 572 °F). Any radioactive contamination in the primary water is confined. Water is circulated by pumps; at lower power levels, reactors designed for submarines may rely on natural circulation of the water to reduce noise generated by the pumps.[citation needed]
The hot water from the reactor heats a separate water circuit in the steam generator. That water is converted to steam and passes through steam driers on its way to the steam turbine. Spent steam at low pressure runs through a condenser cooled by seawater and returns to liquid form. The water is pumped back to the steam generator and continues the cycle. Any water lost in the process can be made up by desalinated sea water added to the steam generator feed water.
In the turbine, the steam expands and reduces its pressure as it imparts energy to the rotating blades of the turbine. There may be many stages of rotating blades and fixed guide vanes. The output shaft of the turbine may be connected to a gearbox to reduce rotation speed, then a shaft connects to the vessel's propellers. In another form of drive system, the turbine turns an electrical generator, and the electric power produced is fed to one or more drive motors for the vessel's propellers. The Russian, U.S. and British navies rely on direct steam turbine propulsion, while French and Chinese ships use the turbine to generate electricity for propulsion (turbo-electric transmission).[citation needed]
Some nuclear submarines have a single reactor, but Russian submarines have two, and so had USS Triton. Most American aircraft carriers are powered by two reactors, but USS Enterprise had eight. The majority of marine reactors are of the pressurized water type, although the U.S. and Soviet navies have designed warships powered with liquid metal cooled reactors.[citation needed]
Marine-type reactors differ from land-based commercial electric power reactors in several respects.[citation needed]
While land-based reactors in nuclear power plants produce up to around 1600 megawatts of net electrical power (the nameplate capacity of the EPR), a typical marine propulsion reactor produces no more than a few hundred megawatts. Some small modular reactors (SMR) are similar to marine propulsion reactors in capacity and some design considerations and thus nuclear marine propulsion (whether civilian or military) is sometimes proposed as an additional market niche for SMRs. Unlike for land-based applications where hundreds of hectares can be occupied by installations like Bruce Nuclear Generating Station, at sea tight space limits dictate that a marine reactor must be physically small, so it must generate higher power per unit of space. This means its components are subject to greater stresses than those of a land-based reactor. Its mechanical systems must operate flawlessly under the adverse conditions encountered at sea, including vibration and the pitching and rolling of a ship operating in rough seas. Reactor shutdown mechanisms cannot rely on gravity to drop control rods into place as in a land-based reactor that always remains upright. Salt water corrosion is an additional problem that complicates maintenance.[citation needed]
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Nuclear marine propulsion
Nuclear marine propulsion is propulsion of a ship or submarine with heat provided by a nuclear reactor. The power plant heats water to produce steam for a turbine used to turn the ship's propeller through a gearbox or through an electric generator and motor. Nuclear propulsion is used primarily within naval warships such as nuclear submarines and supercarriers. A small number of experimental civil nuclear ships have been built.
Compared to oil- or coal-fuelled ships, nuclear propulsion offers the advantage of very long intervals of operation before refueling. All the fuel is contained within the nuclear reactor, so no cargo or supplies space is taken up by fuel, nor is space taken up by exhaust stacks or combustion air intakes. The low fuel cost is offset by high operating costs and investment in infrastructure, however, so nearly all nuclear-powered vessels are military.
Most naval nuclear reactors are of the pressurized water type, with the exception of a few[quantify] attempts[by whom?] at using liquid sodium-cooled reactors. A primary water circuit transfers heat generated from nuclear fission in the fuel to a steam generator; this water is kept under pressure so it does not boil. This circuit operates at a temperature of around 250 to 300 °C (482 to 572 °F). Any radioactive contamination in the primary water is confined. Water is circulated by pumps; at lower power levels, reactors designed for submarines may rely on natural circulation of the water to reduce noise generated by the pumps.[citation needed]
The hot water from the reactor heats a separate water circuit in the steam generator. That water is converted to steam and passes through steam driers on its way to the steam turbine. Spent steam at low pressure runs through a condenser cooled by seawater and returns to liquid form. The water is pumped back to the steam generator and continues the cycle. Any water lost in the process can be made up by desalinated sea water added to the steam generator feed water.
In the turbine, the steam expands and reduces its pressure as it imparts energy to the rotating blades of the turbine. There may be many stages of rotating blades and fixed guide vanes. The output shaft of the turbine may be connected to a gearbox to reduce rotation speed, then a shaft connects to the vessel's propellers. In another form of drive system, the turbine turns an electrical generator, and the electric power produced is fed to one or more drive motors for the vessel's propellers. The Russian, U.S. and British navies rely on direct steam turbine propulsion, while French and Chinese ships use the turbine to generate electricity for propulsion (turbo-electric transmission).[citation needed]
Some nuclear submarines have a single reactor, but Russian submarines have two, and so had USS Triton. Most American aircraft carriers are powered by two reactors, but USS Enterprise had eight. The majority of marine reactors are of the pressurized water type, although the U.S. and Soviet navies have designed warships powered with liquid metal cooled reactors.[citation needed]
Marine-type reactors differ from land-based commercial electric power reactors in several respects.[citation needed]
While land-based reactors in nuclear power plants produce up to around 1600 megawatts of net electrical power (the nameplate capacity of the EPR), a typical marine propulsion reactor produces no more than a few hundred megawatts. Some small modular reactors (SMR) are similar to marine propulsion reactors in capacity and some design considerations and thus nuclear marine propulsion (whether civilian or military) is sometimes proposed as an additional market niche for SMRs. Unlike for land-based applications where hundreds of hectares can be occupied by installations like Bruce Nuclear Generating Station, at sea tight space limits dictate that a marine reactor must be physically small, so it must generate higher power per unit of space. This means its components are subject to greater stresses than those of a land-based reactor. Its mechanical systems must operate flawlessly under the adverse conditions encountered at sea, including vibration and the pitching and rolling of a ship operating in rough seas. Reactor shutdown mechanisms cannot rely on gravity to drop control rods into place as in a land-based reactor that always remains upright. Salt water corrosion is an additional problem that complicates maintenance.[citation needed]
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