C4H
Nuclear fission
Nuclear fission is the splitting of atomic nuclei. Nuclear power stations use the fission of uranium-235( this is an isotope of uranium) to heat water.
How a nuclear power station works
- Fuel produces heat, which is used to boil water to make steam.
- Steam spins a turbine.
- Turbine drives a generator and the generator makes electricity.
- Electricity goes to the transformers to produce the correct voltage.
chain reaction
A chain reaction can carry on for as long as any of the uranium fuel remains.This allows large amounts of energy to be produced
in a nuclear power station the chain reaction is controlled to produce a steady supply of heat.
An nuclear bomb involves if the chain reaction is uncontrolled.
For fission to happen, the uranium nucleus must be hit by a neutron. When this happens:
A neuron is absorbed my nucleus of a uranium 235 atoms
the nucleus is now less stable than before
it splits into two parts
Energy is released
several neutrons are also produces- these may go on strike the nuclei of other atoms causing further fission reactions.
A nuclear reactor
boron control rods are placed between the fuel rods.
boron absorbs the neutrons so fewer neutrons are available to split more uranium nuclei.
the boron rods can be raised or lowered in the reactor, which controls fission rate
enough neutron are always left to keep the process operating.
Nuclear fusion
Nuclear fission is the splitting of large nuclei into smaller ones, while nuclear fusion is the joining of smaller nuclei to make larger ones. Nuclear fusion happens in stars and fusion bombs.
Fusion in power station
Just like nuclear fission, nuclear fusion releases heat energy. However, in nuclear fusion:
two nuclei must join together (rather than uranium nuclei splitting, as in fission)
extremely high temperatures are needed.
Extremely high temperatures are difficult to achieve, and it is difficult to safely manage the extremely hot gases produced.
However, the oceans could provide almost limitless amounts of the hydrogen isotopes needed for nuclear fusion,
so scientists believe that it is worth trying to design and build a fusion power station. This is so expensive that several countries are working together on the project.
The Star
The Sun and other stars use nuclear fusion to release energy. The sequence of nuclear fusion reactions in a star is complex but overall hydrogen nuclei join to form helium nuclei. Here is one nuclear fusion reaction that takes place:
The table summarises the extreme conditions needed for fusion to happen.
cold fusion
A group of scientists have claimed that they have achieved ‘cold fusion – nuclear fusion at ordinary temperatures and pressures. If it happens, cold fusion could be developed to provide almost limitless and cheap electricity. It would also make the international project to develop a fusion power station using high temperatures and pressures pointless.
Problems
There has been difficulty validating the cold fusion results. Some groups of scientists report that it happens while other groups are unable to get it to work. It is important in science that experiments are repeatable, and produce the same or similar results.
Cold fusion is not yet accepted by most scientists, so it is not a realistic method of producing energy at the moment.