| Nuclear Fission | Nuclear fission - the splitting of a large atomic nucleus into smaller nuclei
1) In a nuclear reactor, a neutron is absorbed into a nucleus (uranium-235). Causing nucleus to become uranium-236 => violently unstable
2) Nucleus splits into 2 large fragments - daughter nuclei & 2/3 neutrons explode out of the fission reaction & can collide with other uranium nuclei to cause more fission reactions - Chain reaction
3) The fast moving neutrons carry most of the energy from the reaction with them (99%) but before the neutrons can collide with fresh uranium nuclei, they need to be slowed down so that the energy can pass on to other components in the nuclear reactor, which is used to heat water to drive the turbines that turn the generators |
| Fission Reactors | A fission reactor contains a number of different parts:
1) nuclear fuel (the uranium isotope that will split when triggered by an incoming neutron) - the fuel is held in rods so that the neutrons released will fly out and cause nuclear fission in other rods
2) graphite core - graphite slows the neutrons down so that they are more likely to be absorbed into a nearby fuel rod
3) control rods - these are raised and lowered to stop neutrons from travelling between fuel rods and therefore change the speed of the chain reaction
4) coolant - this is heated up by the energy released from the fission reactions and is used to boil water to drive turbines in the power station
5) concrete shield - the daughter products of the fission reaction are radioactive and can be a hazard
Many of the features of the reactor are designed to control the speed of the reaction and the temperature inside the shielding. An uncontrolled fission reaction is the basis of an atomic bomb |
| Nuclear Fusion | Nuclear fusion - when two small, light nuclei join together to make one heavy nucleus. Fusion reactions occur in stars where two hydrogen nuclei fuse together under high temperatures and pressure to form a nucleus of a helium isotope
1) Many nuclear fusion reactions are happening on the sun. E.g 4 hydrogen nuclei become 1 helium nuclei, causing a missing mass which is converted into energy & radiated away (this is happening on the sun)
2) It is estimated that the sun releases 3.8 × 1026 joules of energy every second
3) Fusion requires fusing of nuclei - positive particles that repel each other when approaching as their the same charge ∴ nuclear fusion must happen quickly so that repulsion doesn't have tine to stop it from happening
4) Particles can travel quickly by being in a hot gas/plasma, the temperature of the hot gas or plasma needs to be at least 150,000,000 degrees Celsius (°C) for fusion to happen |
