How a nuclear reactor makes electricity....?

By:Anubhav

A nuclear reactor produces and controls the release of energy from splitting the atoms of uranium. 

Uranium-fuelled nuclear power is a clean and efficient way of boiling water to make steam which drives turbine generators. Except for the reactor itself, a nuclear power station works like most coal or gas-fired power stations.

What is atomic energy?

 

It's not immediately obvious but tall buildings store energy—potential energy. You have to work hard to lift bricks and other building materials up off the ground into the right position and, as long as they remain where you put them, they can store that energy indefinitely. But a tall, unstable building is bound to collapse sooner or later and, when it does so, the materials from which it was built come crashing back down to the ground, releasing their stored potential energy as heat, sound, and kinetic energy.
Atoms are much the same. Some large atoms are very stable and quite happy to stay as they are pretty much forever. But other atoms exist in unstable forms called radioactive isotopes. They're the atomic equivalents of wobbly old buildings: sooner or later, they're bound to fall apart, splitting into bits like a large building tumbling to the ground and releasing energy on the way. When large atoms split into one or more smaller atoms, giving off other particles and energy in the process, we call it nuclear fission. That's because the central part of the atom (the nucleus) is what breaks up and fission is another word for splitting apart. Nuclear fission can happen spontaneously, in which we case we call it radioactive decay (the conversion of unstable, radioactive isotopes into stable atoms that aren't radioactive). It can also be made to happen on demand—which is how we get energy out of atoms in nuclear power plants. That type of fission is called a nuclear reaction.

The reactor core

Several hundred fuel assemblies containing thousands of small pellets of ceramic uranium oxide fuel make up the core of a reactor. For a reactor with an output of 1000 megawatts (MWe), the core would contain about 75 tonnes of enriched uranium.
In the reactor core the uranium-235 isotope fissions or splits, producing a lot of heat in a continuous process called a chain reaction. The process depends on the presence of a moderator such as water or graphite, and is fully controlled.
The moderator slows down the neutrons produced by fission of the uranium nuclei so that they go on to produce more fissions.
Some of the uranium-238 in the reactor core is turned into plutonium and about half of this is also fissioned similarly, providing about one third of the reactor's energy output.
The fission products remain in the ceramic fuel and undergo radioactive decay, releasing a bit more heat.  They are the main wastes from the process.
The reactor core sits inside a steel pressure vessel, so that water around it remains liquid even at the operating temperature of over 320°C.  Steam is formed either above the reactor core or in separate pressure vessels, and this drives the turbine to produce electricity.  The steam is then condensed and the water recycled.

Common types of reactor

The main design is the pressurised water reactor which has water in its primary cooling/heat transfer circuit, and generates steam in a secondary circuit. The less popular boiling water reactor makes steam in the primary circuit above the reactor core, though it is still under considerable pressure. Both types use water as both coolant and moderator, to slow neutrons.

To maintain efficient reactor performance, about one-third or half of the used fuel is removed every year or two, to be replaced with fresh fuel.
The pressure vessel and any steam generators are housed in a massive containment structure with reinforced concrete about 1.2 metres thick. This is to protect neighbours if there is a major problem inside the reactor, and to protect the reactor from external assaults.
Because some heat is generated from radioactive decay even after the reactor is shut down, cooling systems are provided to remove this heat as well as the main operational heat output.

How does a nuclear power plant work?

Okay, we've figured how to get energy from an atom, but the energy we've got isn't that helpful: it's just a huge amount of heat! How do we turn that into something much more useful, namely electricity? A nuclear power plant works pretty much like a conventional power plant, but it produces heat energy from atoms rather than by burning coal, oil, gas, or another fuel. The heat it produces is used to boil water to make steam, which drives one or more giant steam turbines connected to generators—and those produce the electricity we're after. Here's how:

1. First, uranium fuel is loaded up into the reactor—a giant concrete dome that's reinforced in case it explodes. In the heart of the reactor (the core), atoms split apart and release heat energy, producing neutrons and splitting other atoms in a carefully controlled nuclear reaction.
2. Control rods made of materials such as cadmium and boron can be raised or lowered into the reactor to soak up neutrons and slow down or speed up the chain reaction.
3. Water is pumped through the reactor to collect the heat energy that the chain reaction produces. It constantly flows around a closed loop linking the reactor with a heat exchanger.
4. Inside the heat exchanger, the water from the reactor gives up its energy to cooler water flowing in another closed loop, turning it into steam. Using two unconnected loops of water and the heat exchanger helps to keep water contaminated with radioactivity safely contained in one place and well away from most of the equipment in the plant.
5. The steam from the heat exchanger is piped to a turbine. As the steam blows past the turbine's vanes, they spin around at high speed.
6. The spinning turbine is connected to an electricity generator and makes that spin too.
7. The generator produces electricity that flows out to the power grid—and to our homes, shops, offices, and factories.

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