How Electricity is made PART TWO- NUCLEAR

A nuclear power plant is basically a steam power plant that is fuelled by a radioactive element, like uranium. Nuclear power is generated through a process called “fission”. Fission is what you get when you split an atom into two or more fragments. This releases energy in the form of heat. The heat is then used to boil water, making steam to run the turbines, which turn a generator to make electricity.

  1. First the uranium/Fuel is mined and purified to a fine powder known as “yellow cake” and transported to a Power Station.
  2. The fuel is placed in a reactor and the individual atoms are forced to split apart. The splitting process, known as fission, releases great amounts of energy.
  3. Steam Power Plant: This energy is used to heat water until it turns to steam. The high pressure steam is passed into a turbine.
  4. The expanding steam spins the turbine blades.
  5. The spinning blades turn a shaft connected to a generator
  6. In the generator, magnets spin close to coils of wire.
  7. When this happens, electrical current is produced in the wires.
  8. The electricity generated is transformed into the higher voltages (up to 400,000 volts) used for  economic, efficient transmission via power line grids.
  9. When it nears the point of consumption, such as our homes, the electricity is transformed down to the safer 100-250 voltage systems used in the domestic market.

Why does splitting a uranium atom release energy?

Atoms:

AtomsEverything is made of small particles called atoms. At the centre is the nucleus which consists of protons and neutrons. Moving around the nucleus are electrons. So far, mankind have discovered more than 100 different atoms. The number of protons an atom has is equal to its atomic number and tells us what kind of atom it is. They can be found on the periodic table

For example:

Hydrogen Gas (H) = one proton

Oxygen (0) = eight protons

Uranium (U) = ninety two protons

The image has three protons so its atomic number is 3 and this is Lithium (Li), the third element on the periodic table.

Nuclear Energy:

fission_lgThere is energy stored in the nucleus of an atom this is referred to as nuclear energy. Neutrons are the glue/energy that holds atoms together; therefore to use the energy we have to separate the neutrons. We can split one atom into two smaller atoms this is call fission.

Under the right conditions, a uranium atom will split into two smaller atoms and throw off two or sometimes three neutrons in the process. The smaller atoms don’t need all the energy that held the larger atom together. The extra energy is released as heat and radiation.

Where do the extra neutrons go when the atom splits?

The neutrons hit other atoms in the reactor core, starting a chain reaction. Initially, about 3 or 4 percent of the uranium atoms are uranium-235 — the same as the first set of atoms that split. If these atoms are hit with neutrons, they split readily and throw off more energy and neutrons.

But the other 96 or 97 percent of the uranium atoms in the core initially are of a type that is hard to split, known as uranium-238. If hit with a neutron, a uranium-238 atom will absorb the neutron and eventually turn into plutonium-239. It’s not until these plutonium atoms are hit again with more neutrons that they finally split and release energy.

From here, the mechanics of a steam power plant take over. The steam pushes on turbines, which force coils of wire to interact with a magnetic field. This generates an electric current.

Nuclear and the environment:

The use of nuclear power as a source of domestic energy has increased significantly over the past decade and is expected to continue to do so in the years to come. However, the use of this form of energy does not come without a unique set of consequences. Unlike burning fossil fuels, using nuclear fission to generate electricity produces no soot or greenhouse gases. This helps keep the skies clean and doesn’t contribute to global warming. However there are still dangers and concerns that come with nuclear energy.

–          Nuclear waste is the spent nuclear fuel from a reactor. The fuel is considered spent when the fission byproducts — the atoms left over from the splitting process — prevent free neutrons from splitting more uranium or plutonium. It takes three or four years to get to this point in the process. The waste is highly radioactive, so it must be stored in steel-lined concrete pools or in dry caskets.  Disposing of the wastes is a problem. One way is dropping a container of waste into a hole 100-150 feet deep at the bottom of an ocean. It is also buried in deep holes on land, far away from where anyone lives. Nuclear reactors must be sheathed in massive concrete and lead walls to prevent radiation from escaping or leaking into the environment. Exposure to too much radiation has been directly linked to causing cancer.

–          Containment. The structure around the reactor core which is designed to protect it from outside intrusion and to protect those outside from the effects of radiation in case of any major malfunction inside. It is typically a metre-thick concrete and steel structure. However Nuclear power plant in any region have social consensus and a risk perceptions of people living in the vicinity of such a plant. People in such regions fear the threat of being exposed to unusual levels of radiation. A major failure in a nuclear power plant’s cooling systems can create a nuclear meltdown, where fuel rods melt within a matter of seconds. The heat from the uncontrolled reaction can melt everything it comes into contact with. Catastrophic accidents could injur or kill thousands of people. What happens if something goes wrong?

Factbox: Key facts on Chernobyl nuclear accident

LINK: http://www.reuters.com/article/2011/03/15/us-nuclear-chernobyl-facts-idUSTRE72E42U20110315

–          Mining and Transportation:

Uranium 308 is most typically mined in the form of a rock containing the mineral. A high rate of ore is around 7% in un purified uranium. Less common is the extraction from “heavy water”

Hard rock mining

In most instances, the ore is removed from the ground using conventional underground and surface mining techniques.

The rock is blasted in the ground to break it into smaller, easier to manage and process pieces.

From here it is loaded onto trucks and taken to a large primary crusher, then through to secondary and tertiary crushing circuits. After this process the ore is ground into a fine (0.015mm) paste in large rotating drums called mills.

The ground paste is then fed through an acidic gravitational flotation process, then on to a solvent extraction plant.

The remaining product is kiln dried to produce the final product “yellow cake” to be distributed to power plants.

Nuclear and energy efficiency:

One ounce of uranium (nuclear fuel) contains the same amount of energy as ninety tons of coal!

The fuel used to power nuclear reactors is very compact in comparison to fossil fuels. For instance, one pound of uranium can supply the same energy as 3 million pounds of coal. Therefore nuclear power is much more efficient. This makes it attractive for use in nuclear-powered vehicles like submarines, aircraft carriers and spacecraft.

Author

KONICA MINOLTA DIGITAL CAMERARachel McCann

Project Manager

Photovoltaic Lighting Group

 

By understanding the different processes of creating electricity we are able to use the most sustainable methods for everyday use such as lighting our streets and Parks. At PLG we specialise in being able to custom design standalone solar lighting system for our customers’ requirements.

LIGHTING THE WAY OF THE FUTURE

Categories: Sustainability

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