Nuclear fission is the splitting of an atomic nucleus. There are two fissionable isotopes in common use in nuclear reactors - uranium-235 and plutonium-239. Naturally occuring uranium is mostly uranium-238, which is non-fissionable. Most nuclear reactors use enriched uranium that contains 2-3% uranium-235. For fission to occur, the uranium-235 or plutonium-239 nucleus must absorb a neutron. The nucleus then splits into two smaller nuclei. In this process, two or three neutrons are emitted and energy is released. The energy released in this nuclear process is much greater than the energy released in a chemical process such as burning. A chain reaction occurs when each fission event causes further fission events. In a nuclear reactor the process is controlled, so one fission per fission on average goes on to produce further fission.
Nuclear fusion is the process of forcing two nuclei close enough together so they form a single, larger nucleus. Nuclear fusion can be brought about by making two light nuclei collide at very high speed. Fusion is the process by which energy is released in stars. There are enormous problems with producing energy from nuclear fusion in reactors. Nuclei approaching each other will repel one another due to their positive charge. To overcome this, the nuclei must be heated to very high temperatures to give them enough energy to overcome the repulsion and fuse. Because of the enormously high temperatures involved, the reaction cannot take place in a normal container but has to be contained by a magnetic field.
The major source of background radiation is radon gas which seeps through the ground from radioactive substances in rocks deep underground. Radon gas emits alpha particles, so it is a health hazard if it is breathed in. Other sources of background radiation include cosmic rays from outer space, food and drink, air travel and nuclear weapons testing. Medical sources of background radiation include X-rays (these have an ionising effect), as well as radioactive substances.
Uranium and plutonium are chemically removed from used fuel rods from nuclear reactors, as…