How would a fusion reactor differ from the nuclear reactors you currently have?

Answer 1

The nuclear reactors we have now are fission reactors. This means that they obtain their energy from nuclear reactions that split large nuclei such as uranium into smaller ones such as rubidium and cesium. There is a binding energy that holds a nucleus together. If the binding energy of the original large nucleus is greater than the sum of the binding energies of the smaller pieces, you get the difference in energy as heat that can be used in a power station to generate electricity.

A fusion reaction works the other way. It takes small nuclei like deuterium (heavy hydrogen) and fuses them together to make larger ones such as helium. If the binding energy of the two deuterium nuclei is greater than that of the final larger helium nucleus, it can be used to generate electricity.

There are two main differences between fission and fusion. The first is that the materials required for fission are rarer and more expensive to produce than those for fusion. For example, uranium has to be mined in special areas and then purified by difficult processes. By contrast, even though deuterium makes up only 0.02 percent of naturally occurring hydrogen, we have a vast supply of hydrogen in the water making up the oceans. The second difference is that the products of fission are radioactive and so need to be treated carefully, as they are dangerous to health. The products of fusion are not radioactive (although a realistic reactor will likely have some relatively small amount of radioactive product).

The problem with building fusion reactors is that a steady, controlled fusion reaction is very hard to achieve. It is still a subject of intense research. The main problem is that to achieve fusion we need to keep the nuclei we wish to fuse at extremely high temperatures and close enough for them to have a chance of fusing with one other. It is extremely difficult to find a way of holding everything together, since the nuclei naturally repel each other and the temperatures involved are high enough to melt any solid substance known. As technology improves, holding everything together will become easier, but it seems that we are a long way off from having commercial fusion reactors.