Nuclear Fusion is where two nuclei join together into one. It is usually two lighter nuclei making one heavier nuclei, meaning that energy is given out. This process is the reverse of nuclear fission, but it needs more heat to start the reaction, and therefore is much more dangerous.It takes more energy to start the reaction as the nuclei both have posiitive charges which require huge amount of energy to overcome the repulsion between the two positively charged nuecli which is why high temeratures are needed. At the moment, there are no nuclear power stations using fusion, although there are plans to build one in France.
Often, Deuterium and Tritium (two isotopes of hydrogen) join to make Helium, a neutron and large amounts of energy.
However, the temperature is needed to be over 100 millionC on Earth, whereas on the sun, where this also takes place; the pressure is a lot greater, meaning that the temperature can be lower.
Fusion bombs are approximately 1,000 times more powerful than their fission counterparts. They are also called hydrogen bombs or H-bombs, as the substances used in them are both isotopes of hydrogen. As fusion needs incredibly high temperatures to take place, hydrogen bombs are activated using a fission reaction.