Uranium (nuclear)

Nuclear energy is energy in the nucleus (core) of an atom. Atoms are tiny particles that make up every object in the universe. There is enormous energy in the bonds that hold atoms together.
Nuclear energy can be used to make electricity. But first the energy must be released. It can be released from atoms in two ways: nuclear fusion and nuclear fission.

In nuclear fusion, energy is released when atoms are combined or fused together to form a larger atom. This is how the sun produces energy.

In nuclear fission, atoms are split apart to form smaller atoms, releasing energy. Nuclear power plants use nuclear fission to produce electricity.

Nuclear Fuel
Atoms are made up of three major particles:  protons, neutrons and electrons.  The most common fissionable atom is an isotope (the specific member of the atom's family) of uranium known as uranium-235 (U-235 or U 235 ), which is the fuel used in most types of nuclear reactors today.  Although uranium is quite common, about 100 times more common than silver, U-235 is relatively rare. 
 


Nuclear power plants generate electricity
Most power plants burn fuel to produce electricity, but not nuclear power plants. Instead, nuclear plants use the heat given off during fission as fuel. Fission takes place inside the reactor of a nuclear power plant. At the center of the reactor is the core, which contains the uranium fuel.

The uranium fuel is formed into ceramic pellets. The pellets are about the size of your fingertip, but each one produces the same amount of energy as 150 gallons of oil. These energy-rich pellets are stacked end-to-end in 12-foot metal fuel rods. A bundle of fuel rods is called a fuel assembly.

Fission generates heat in a reactor just as coal generates heat in a boiler. The heat is used to boil water into steam. The steam turns huge turbine blades. As they turn, they drive generators that make electricity. Afterward, the steam is changed back into water and cooled in a separate structure at the power plant called a cooling tower. The water can be used again and again.

Types of reactors
Just as there are different approaches to designing and building airplanes and automobiles, engineers have developed different types of nuclear power plants. Most popular of them are: boiling-water reactors (BWRs), and pressurized-water reactors (PWRs).

In the BWR, the water heated by the reactor core turns directly into steam in the reactor vessel and is then used to power the turbine-generator. In a PWR, the water passing through the reactor core is kept under pressure so that it does not turn to steam at all -- it remains liquid. Steam to drive the turbine is generated in a separate piece of equipment called a steam generator. A steam generator is a giant cylinder with thousands of tubes in it through which the hot radioactive water can flow. Outside the tubes in the steam generator, nonradioactive water (or clean water) boils and eventually turns to steam. The clean water may come from one of several sources: oceans, lakes or rivers. The radioactive water flows back to the reactor core, where it is reheated, only to flow back to the steam generator.

Nuclear reactors are basically machines that contain and control chain reactions, while releasing heat at a controlled rate. In electric power plants, the reactors supply the heat to turn water into steam, which drives the turbine-generators. The electricity is shipped or distributed through transmission lines to homes, schools, hospitals, factories, office buildings, rail systems and other customers.


Nuclear Steam Supply System:



The reactor core is composed of four main elements:
THE FUEL.  Nuclear fuel consists of pellets of enriched uranium dioxide encased in 12-foot long pencil-thick metal tubes, called fuel rods.   These fuel rods are bundled to form fuel assemblies.  A nuclear plant can operate continuously for up to 2 years.  To run this long, a reactor must have as many as 100 to 300 fuel assemblies.

THE CONTROL RODS.  The control rods contain material that regulates the rate of the chain reaction.  If they are pulled out of the core, the reaction speeds up.  If they are inserted, the reaction slows down.

THE COOLANT. A coolant, usually water, is pumped through the reactor to carry away the heat produced by the fissioning of the fuel.  This is comparable to the water in the cooling system of a car, which carries away the heat built up in the engine.  In a reactor, as much as 330,000 gallons of water flow through the reactor core every minute to carry away the heat.

THE MODERATOR.  A moderator, water, slows down the speed at which atoms travel. This reduction in speed actually increases the opportunity to split, thereby releasing energy.

Although engineering designs are quite complex, these four elements -- the fuel, the control rods, the coolant and the moderator -- are the basic components of a nuclear reactor.


Nuclear power and the environment
Like all industrial processes, nuclear power generation has by-product wastes: radioactive waste and heat.  Nuclear generated electricity does not emit carbon dioxide into the atmosphere.

Radioactive wastes are the principal environmental concern for nuclear power.  Most nuclear waste is low-level nuclear waste.  It is ordinary trash, tools, protective clothing, wiping cloths and disposable items that have been contaminated with small amounts of radioactive dust or particles.  These materials are subject to special regulation that govern their storage so they will not come in contact with the outside environment.

 

On the other hand the irradiated fuel assemblies are highly radioactive and must be stored in specially designed pools resembling large swimming pools (water cools the fuel and acts as a radiation shield) or in specially designed dry storage containers.  Most nuclear fuel is stored under water. A few reactors store their older and less radioactive fuel in dry storage facilities outside using special concrete or steel containers with air cooling.
 
 
     

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