Nuclear Power Plant

 Nuclear reactor

A nuclear reactor produces heat that drives a steam turbine, which in turn drives a propeller. There are three main types of marine reactors: pressurized water reactors, natural circulation reactors, and liquid metal reactors and click here for submarine.

 

Typically, uranium produces heat in a nuclear reactor by nuclear fission. In a nuclear reactor, the uranium is surrounded by a moderator, which is required to slow down the reacting neutrons so that they can interact with the uranium more efficiently. In most reactors, the moderator is water, which is also used to remove the heat of reaction. This heated water is called the primary circuit water. The water, which is under pressure to prevent boiling, flows through a heat exchanger where the heat is transferred to a separate secondary water circuit. The heat exchanger is essentially a boiler, and the secondary circuit or loop actually provides the steam that drives the turbine. As long as proper seals are ensured, water from the primary circuit cannot contaminate the rest of the power plant.

 

In most cases, the water in the primary circuit is circulated by a pump. The reactor can also be arranged so that water circulates naturally, for example due to the temperature difference between the part of the reactor containing the reacting fuel and the rest of the reactor. Typically in these natural circulation reactors, cooled water is piped from a heat exchanger to the bottom of the reactor and rises while heating the fuel assemblies.

 

Liquid metal cooled reactors work on the principle that molten metal can carry much more heat than water can, and therefore allow the use of more compact turbines. However, this advantage is undermined by the fact that the molten metal can become highly radioactive, making leaks, already dangerous enough in pressurized hydroelectric plants, even more dangerous. Secondly, the pumps in these reactors must be more powerful, and the simplicity of using the same material as moderator and heat sink is lost. And finally, there is always the possibility of losing a lot of heat, clogging the system and causing the metal in the pipes to solidify, with catastrophic consequences.