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Like a conventional submarine, a nuclear submarine also works on the same principle and construction design; however the only difference between them is the method of propulsion. A conventional submarine uses diesel engines or electric batteries or a combination of both. However, there are several problems related to this type of propulsion system when used in submarines. Problems such as diesel engine emissions, re-fuelling or recharging of batteries, and the inability to stay underwater for a long time are the main ones among them. The introduction of nuclear submarines along with a few changes in the submarine design eradicated all these problems and brought a revolution in the submarine world.
Image Credits : Nuclear submarine at fas website (http://www.fas.org/irp/dia/product/art/96_970.jpg)
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Nuclear Submarine Design and Construction
Like a conventional submarine, the design of a nuclear submarine also consists of two hulls – inner and outer hulls. The outer hull provides a streamlined shape to the submarine, whereas the inner hull protects the interiors from extreme pressures at greater ocean depths. The hulls are generally made from an alloy which is a combination of nickel, molybdenum, and chromium. Between these two hulls are located the ballast tanks, which take in or release water to ascend or descend the submarine as per the requirement. Most of the submarines are also provided with trim tanks, located at the forward and aft of the submarine, used for increasing the stability of the submarine.
The direction of the submarine is guided with the help of rudder and stern plates. The rudder is vertically aligned whereas the stern plate is horizontally aligned. The former controls the lateral movement whereas the later controls the vertical movement. A propeller is located at the rear end of the submarine and is driven by a steam turbine or diesel generators or a combination of both. However, in a nuclear turbine the propulsion power is generated using a nuclear reactor.
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Nuclear Submarine Propulsion System
A nuclear reactor is an air tight enclosed space wherein uranium atoms split to generate huge amount of energy. When the uranium atoms split, they release massive energy along with heat and radiation. This released heat is channelized to propel the submarine. This is generally done in two ways –
The heat released is used to heat up water after passing through a compartment surrounding the reactor. The water is circulated in this compartment at extremely high pressure which prevents it from getting converted into steam. Heated water from the compartment is then allowed to flow through a series of coils containing water at normal temperature, which in turn gets converted into a huge amount of steam. The steam is then transferred to steam turbine where the engergy it is converted into electricity and later used for propulsion. Nuclear fission generates a huge amount of energy, which allows the submarine to avoid having to come to the surface for several months.
Some of the advanced submarines have reactors that directly convert the heat generated into electrical energy. The electrical energy is then used to power electric motors which are connected to the propeller shaft of the submarine.
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Advantages and Disadvantages
The main advantage of a nuclear submarine is that it is not required to be refuelled and brought to the surface again and again. However, most of the nuclear submarines have diesel generators as an alternate power source which is used in case of a fault in the nuclear reactor.
However, the biggest disadvantage of a nuclear reactor submarine is that the reactor needs to be cooled continuously even when the submarine is not moving. Moreover, nuclear fission generates huge amounts of harmful radiation, which if leaked, can damage both human and marine life. In case of reactor failure or leakage, an unimaginable level of damage is done to the surrounding area. It is for this reason nuclear reactors are considered extremely dangerous.
Also, as the reactor is cooled using surrounding sea water, the nuclear submarine moves ahead leaving behind a trail of warm water. This warm water layer rises to the surface and creates a "thermal wake" which can be easily detected by a thermal imaging system.