Physics - Fission and Fusion

Power stations use energy sources to produce electricity.

Conventional power stations burn fossil fuels (coal, oil and gas). This produces the heat required to make steam. The nuclear reaction is called fission.

Both power stations then use the steam to drive turbines, which turn generators and produce electricity.

Nuclear fission  is the process by which heat energy is released when a radioactive nucleus (i.e. uranium) splits. This heat energy can be used in a nuclear reactor.

When a uranium nucleus absorbs an extra neutron it splits, releasing energy and more neutrons. These neutrons can then cause further uranium nuclei to split. This is called a chain reaction.

Nuclear fission produces radioactive waste, which can be dangerous.

A nuclear bomb is a chain reaction that has gone out of control. It results in one powerful release of energy.

Nuclear fusion is the process by which heat energy is released when nuclei join (fuse) together. Fusion happens easily in stars, but is not yet a practical energy source in the earth.

Small Scale Nuclear Fission

1. The uranium atom is hit with a neutron.

2. The nucleus splits into two smaller nuclei (e.g. barium and krypton).

3. Energy and new neutrons are released.

The new atoms formed (barium ans krypton), are themselves radioactive.

Scientists stop nuclear reactions getting out of control by placing control rods in the reactor.

The rods absorb some of the neutrons (preventing further fissions).

They can be lowered or raised to control the number of neutrons available for fission, which allows the process to keep operating safely.

When two nuclei join (fuse) together a large amount of heat energy is released. This can only happen at extremely high temperatures. It is very difficult to manage these high temperatures so nuclear fusion is not yet a possible energy source on the earth.

An example of a fusion reaction is when two hydrogen nuclei join to form a helium nucleus. This takes place in stars and fusion bombs (hydrogen bombs).

Different isotopes of hydrogen can be undergo fusion:

In stars, fusion happens very easily. On earth, scientists have not yetbeen able to produce extremely high temperatures and pressures needed to keep a fusion reaction going long enough for a practical power generation. In a fusion bomb the initial high temperautres needed are produced by a fission reaction.

Ordinarily, fusion reactions require extremely high temperatures and pressures for two nuclei to fuse (join) together. When two nuclei fuse, energy is released. For decades, scientists have been attempting to reproduce fusion reactions under controlled conditions in laboratories. If the reaction can be controlled the energy released could be harnessed and used as an alternative energy source, replacing fossil fuels. Cold fusion refers to a fusion reaction that occurs at room temperature.

In 1989 Martin Fleischmann and Stanley Pons claimed to have achieved a cold fusion reaction. When a new discovery is made, it's important to share data with other scientists. Scientists from across the world are then able to try and replicate the experiment. They must check that the experiment can be repeated and that the same data can be produced. This shows the discovery is genuine and it doesn't show anomalous results (errors). It's only when experiment are repeated, and matching ata collected (over and over again) that a new theory can be accepted.