How a nuclear power plant works?

This post is about what is nuclear fission energy and how a nuclear power plant works.

Nuclear fission energy

The nuclear power plant uses the energy which come from nuclear reaction of uranium U-235 with a neutron. When a neutron hit a U-235 nucleus, it become U-236 and become unstable, divide itself in two nucleus, one of Barium and one of Krypton, releasing a great quantity of energy and many particles, including neutrons and gamma ray.

The released neutrons hit others U-235 nucleus, creating a chain reaction.

85% of reactions with U-235 produce fission, while other 15% produce U-236 and gamma rays, which are high energy photons.

The energy generated in these reactions is calculated by the equation which everybody have heard of.

$E=mc^2$

The mass is very small, however, multiplying by the speed of light squared, gives a great quantity of energy. Without include the chain reaction. An uncontrolled chain reaction is used in atomic bombs, while controlled reactions are used in power plants and propulsion systems.

The first neutron

From where come the first neutron to execute the chain reaction? One of the sources can be the Californium-252, which emits neutrons spontaneously.

Another source can be the Americium-241, which emits gamma and alfa (helium nucleus) particles, when they hit beryllium nucleus, it release neutrons. It is possible to use plutonium isotopes instead Americium-241. The U-235 emits spontaneously alfa particles and can initiate chain reaction.

$He^4+Be^9 \rightarrow C^12+n^1+5,7MeV$

$\gamma + Be^9 \rightarrow Be^8+n^1-1,66 MeV$

$U^{235}_{92}\rightarrow Th^{231}_{90}+He^{4}_{2}$

The working of power plant

A nuclear power plant is a thermal power plant, by that, has water to generate steam to turn a turbine. The difference is in how to heat the boiler. These are uranium bars used in nuclear reactors.

The nuclear fuel assembled to put in the reactor.

In the figure below, there is a typical nuclear reactor. The nuclear reaction needs to be controlled and provide stable levels of energy, therefore, are used control bars made of materials which absorb neutrons like boron, silver, indium or cadmium. These bars are controlled by electromagnets which lift the bars.

The moderator, which surrounds the fuel, is made of graphite, and also serves to control the chain reaction. The own water is used to control reaction and temperature. The reactor stays inside a structure made of steel and reinforced concrete, to protect against radiation leak.

Types of reactors

In boiling water reactors, the steam is generated in the reactor and goes to the turbine.

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In pressurized water reactors, the steam is generated outside the reactor.

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