This section deals with the theory and operation of nuclear fission reactors as a practical energy source. Over 30 countries around the world now operate nuclear power stations, and many countries are heavily reliant on nuclear power. Around 17% of the world's electricity now comes from nuclear energy. The World Nuclear Association in London is a good site to start for general information. If your browser can handle PDF files, then I particularly recommend their factsheets.
The theoretical basis for fission is the massive energy
release which occurs when a heavy nucleus divides into two smaller
ones. Only a few very heavy nuclei undergo fission spontaneously,
while others can be encouraged to undergo fission by the addition of
energy when a neutron is absorbed. Such fissile materials (as they are
known) include 235U and 239Pu.
During the fission process, a number of neutrons are released, and if these go on to induce new fission events, a chain reaction results. The use of a controlled chain reaction is the basis for all nuclear power stations.
The most common reactor types are the pressurised water reactor (PWR), the boiling water reactor (BWR) and the Russian RBMK design. The properties of the key reactor types are summarised below:
| Type | Fuel | Moderator | Coolant | Number in use |
|---|---|---|---|---|
| PWR | Enriched Uranium | Water | Water | 252 |
| BWR | Enriched Uranium | Water | Water | 93 |
| CANDU | Natural Uranium | Heavy Water | Heavy Water | 33 |
| GCR (inc Magnox) | Natural Uranium | Graphite | CO2 | 21 |
| AGR | Enriched Uranium | Graphite | CO2 | 14 |
| LWGR(inc RBMK) | Enriched Uranium | Graphite | Water | 15 |
Nuclear power plant safety depends on a number of key issues including plant design, operator training and operating procedures.