What is a nuclear submarine? How is it different from a normal submarine?

Produced by: Science Popularization China

Author: Cui Yongjie

Planning: Zhao Qingjian

Producer: Guangming Online Science Department

Netizens asked: What is a nuclear submarine? How is it different from a normal submarine?

Expert Answer:

Nuclear submarines use high-pressure steam generated by nuclear reactors to drive steam turbines to propel submarines. The nuclear power plant of a nuclear submarine consists of a nuclear reactor, a circulating pump, a steam generator and a turbine. Since the nuclear power plant does not rely on air, nuclear submarines can stay underwater for a long time without surfacing.

A conventional submarine is a submarine that is powered by a diesel engine, a battery, and an electric motor. It is also called a diesel-electric submarine. When sailing on the surface, the diesel engine is used as power to charge the battery. When diving, the battery is used to power the electric motor to drive the submarine. Since early submarines used lead-acid batteries with limited energy storage capacity, their underwater diving time was very short and their speed was very low, which greatly affected their combat capability and concealment.

French Triomphant-class strategic missile nuclear submarine (picture from the Internet)

From the appearance, nuclear submarines are large in tonnage due to the large size of their nuclear power plants, and are classified as large submarines, with some having a displacement of up to 4,000 to 5,000 tons. Nuclear submarines are submerged for a long time and basically do not need to consider sailing on the surface. Their appearance is teardrop-shaped to reduce the resistance of underwater navigation. The speed of nuclear submarines underwater is also amazing, up to more than 30 knots. It is difficult for ordinary ships to catch up.

Conventional submarines have limited submergence time and have to consider the performance of surface navigation at the same time, so they have continued to use the hull shape of the ship. With the advancement of technology, many conventional submarines have also begun to adopt a teardrop-shaped design. In addition to diesel engine motor drive, an AIP power unit is also installed to further improve the submergence capability. For example, Japan's "Soryu" class submarine "Huanglong" also uses lithium-ion batteries instead of lead-acid batteries. Its underwater submergence capability has approached or reached 14 days. The maximum underwater submergence time of a nuclear submarine is 80 to 90 days. However, considering the physiological and psychological tolerance of humans, the general underwater submergence time of a nuclear submarine is about 14 days. That is to say, due to the development of science and technology, the submergence time of conventional submarines has approached the lower limit of nuclear submarines, but the speed is still not comparable to that of nuclear submarines, with a maximum of about 20 knots.

Although nuclear submarines have almost unlimited cruising capabilities, their nuclear fuel has the problem of radioactive contamination. Disposal of submarine nuclear waste is a very troublesome problem. In contrast, conventional submarines are much less harmful to the environment.

Cui Yongjie: Marine military science expert, works at the 714th Research Institute of China Shipbuilding Industry Corporation, senior engineer, mainly engaged in the research of high-precision digital model simulation and stealth of domestic and foreign naval ships, submarines and combat aircraft. The research results are mainly used in the identification, tracking and locking of targets by radar and missile equipment, and the optimization design of stealth of ships, aircraft and other vehicles.