The nuclear power plant stands on the border between humanity’s greatest hopes and its deepest fears about the future. On one hand, atomic energy offers a clean energy alternative that frees us from the shackles of fossil fuel dependence. On the other, it summons images of disaster; quake-ruptured Japanese power plants belching radioactive steam, the dead zone surrounding Chernobyl’s concrete sarcophagus.
Electricity was generated by a nuclear reactor for the first time ever on 20 December 1951, at the EBR-I experimental station near Arco, Idaho in the United States. On 27 June 1954, the world’s first nuclear power plant to generate electricity for a power grid started operations at Obninsk in the Soviet Union. The world's first commercial scale power station, Calder Hall in England opened on 17 October 1956.
Statistics speak as of 1 March 2011, there were 443 operating nuclear power reactors spread across the planet in 47 different countries. In 2009 alone, atomic energy accounted for 14 percent of the world's electrical production.
What happens inside a nuclear power plant to bring such marvel and misery into being?
Nuclear Power Plants in a Nutshell
Nuclear energy usually means the part of the energy of an atomic nucleus that can be released by fusion or fission or radioactive decay. The term “Nuclear Power” means the use of sustained nuclear fission to generate heat that can be utilized to generate electricity.
The idea of an atom began with the Greek philosopher Democritus, who claimed all matter consisted of little tiny particles; he called them “atomos”, the Greek word for “invisible”. He could not prove they existed though; centuries later, however, other scientists did. That discovery heralded the nuclear power movement, which has been sparking controversy and debate ever since.
Nuclear energy is utilized in a facility that we know as the “Nuclear Reactor: an environment designed to initiate and control a sustained nuclear chain reaction. A nuclear power plant is a thermal power station in which the heat source is a nuclear reactor.
As is typical in all conventional thermal power stations, the heat is used to generate steam, which drives a steam turbine connected to a generator that produces electricity. Nuclear power plants are usually considered base load stations. This means that a very small amount of fuel can produce the target required amount of power; hence, fuel is a small part of the cost of production, while the major cost of production lies within the construction and operation of the facility itself.
Nuclear Power Plants Anatomy
Imagine following a volt of electricity back through the wall socket, all the way through miles of power lines to the nuclear reactor that generated it. You would encounter the generator that produces the spark and the turbine that turns it. Next, you would find the jet of steam that turns the turbine, and finally the radioactive uranium bundle that heats water into steam at the core of the reactor.
The water in the reactor serves as a coolant for the radioactive material, preventing it from overheating and melting down. In March 2011, viewers around the world became well acquainted with this reality as Japanese citizens fled by the tens of thousands from the area surrounding the Fukushima-Daiichi nuclear facility after the most powerful earthquake on record and the ensuing tsunami inflicted serious damage on the plant and several of its reactor units. Among other events, water drained from the reactor core, which in turn made it impossible to control core temperatures, resulting in overheating and a partial nuclear meltdown.
The conversion to electrical energy takes place indirectly, as in conventional thermal power plants. The heat is produced by fission in a nuclear reactor; directly or indirectly, water vapor—steam—is produced; the pressurized steam is then usually fed to a multi-stage steam turbine.
Steam turbines in the average nuclear power plant are among the largest steam turbines ever. After the steam turbine has expanded and partially condensed the steam, the remaining vapor is condensed in a condenser—a heat exchanger that is connected to a secondary side such as a river or a cooling tower. The water is then pumped back into the nuclear reactor and the cycle begins again; the water-steam cycle corresponds to what engineers know as “The Rankine cycle”.
To make things simpler, let us just say that the basic part of the nuclear power plant is the nuclear reactor; and the basic part of the nuclear reactor is the “reactor core”, which is where the nuclear fuel is—uranium for example. The fuel is placed in the reactor core in the form of fuel rods that are arranged with what is known as “control rods”, which rigidly controls the rate of the reaction.
When the reactor is started, a nuclear fission reaction—chain reaction—takes place and the rate of this reaction is controlled in a way that the reaction does not precede too fast or too slow and the amount of thermal energy—heat—generated by the reaction is accurately calculated and controlled.
In order to sustain the reactor core at the same temperature, the heat generated by the reaction has to be absorbed by a continuous cooling stream of water. Once the water absorbs the heat of the reaction, it turns into super-heated steam, which is withdrawn from the reactor and introduced into a steam turbine where the steam—at high pressure and temperature—turns the blades of the turbine at extremely high speed converting the thermal energy into useful kinetic energy. The turbine will simultaneously rotate an electrical generator that is mounted with it on the same axis and the generator will convert the kinetic energy into electricity.
If the chain reaction goes too fast, it can generate more heat than the water can carry away; or if something happens to the cooling, the core can get so hot that it will start to melt. Once it melts, the chain reaction continues uncontrolled so the temperature rises even more and the core melts down through the concrete and steel, and if it gets far enough, down into the ground.
The molten core will diffuse into the surrounding media—layers of the ground for instance—until it gets diluted enough by this media that the chain reaction slows down; when the core loses its heat, the whole mass cools enough to solidify. It will remain physically and radioactively hot for many years. This melt down is what happened at Chernobyl in Ukraine back in the days of the Soviet Union and a lot of people were killed by high radiation and a lot of radioactive dust contaminated the land around the reactor.
References
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