• When large atomic nuclei are hit with neutrons they can become highly unstable if the neutron is absorbed by the nucleus. The larger unstable nucleus breaks into two smaller 'daughter' nuclei and also release more neutrons, as well as beta and alpha particles and gamma.

• The two smaller atoms formed are themselves usually unstable and radioactive.

  • The nuclear fission equations below are a gross simplification of the process!

• This process is called nuclear fission and because it is accompanied by an enormous release of energy, it forms the basis of nuclear power.

• The radioisotope uranium-235  is particularly useful for energy generation by nuclear fission.

• Much of the energy released is initially the kinetic energy of the fission fragments, but collisions, radioactive decay etc. result in most of it changing to heat and some as electromagnetic radiation.

• The nuclear fission process of energy release is carried out under controlled conditions in a nuclear reactor.

  • The nuclear reaction must be well sealed with thick walls of concrete and steel.

  • Heat exchange pipes of water or carbon dioxide convey the heat from the reactor to the boilers which generate the steam to drive the steam turbines and generators.

• The heat energy can be used to boil water to make steam to drive a turbine and electrical generator in a nuclear power station.

• The energy release is much greater than for exothermic chemical reactions eg 1g uranium nuclear fuel releases the same amount of energy as 1 tonne of coal (= 1000kg =  1000000g), a million x energy density factor!

• One consequence of fission is that more neutrons are formed, these in turn 'split' other atoms making even more neutrons.

• This is called a chain reaction and leads to acceleration in the atom 'splitting' and hence an even greater energy release.

• If uncontrolled a nuclear explosion results (a fission bomb based on uranium-235 was dropped on the Japanese city of Hiroshima in 1945, Nagasaki was hit by a plutonium based fission bomb).

• In nuclear reactors, rods of a 'moderator' like boron can lowered into the reactor core to absorb neutrons and slow down fission to keep the chain reaction under control. Note again, the balancing of nuclear equations for, in this case, fission reactions (somewhat simplified!) ...

uranium splits into lanthanum and bromine nuclei

uranium split into molybdenum and lanthanum and a good balancing challenge!

• When the spent uranium nuclear fuel is removed from a nuclear reactor, it is sent for reprocessing.

  • This is an extremely complicated and costly process.

  • However, one idea was to extract plutonium metal, which is formed as a natural 'nuclear consequence' of the nuclear reactions in a uranium nuclear reactor.

  • Plutonium, like uranium, is a readily fissile material i.e. it readily undergoes fission under neutron bombardment to release considerable quantities nuclear energy.

• Unfortunately there is considerable amounts of highly radioactive waste from the nuclear power industry which must be disposed of safely. See health and safety, half-life of radioisotopes and background radiation

or Harder-Higher Radioactivity Quiz

  five word-fills on radioactivity * Q2 * Q3 * Q4 * Q5and ANSWERS!

crossword puzzle on radioactivity and ANSWERS!

Revision KS4 Science GCSE/IGCSE/O level Chemistry Information Study Notes for revising for AQA GCSE Science, Edexcel 360Science/IGCSE Chemistry & OCR 21stC Science, OCR Gateway Science  WJEC gcse science chemistry CCEA/CEA gcse science chemistry O Level Chemistry (revise courses equal to US grade 8, grade 9 grade 10) A level Revision notes for GCE Advanced Subsidiary Level AS Advanced Level A2 IB Revise AQA GCE Chemistry OCR GCE Chemistry Edexcel GCE Chemistry Salters Chemistry CIE Chemistry, WJEC GCE AS A2 Chemistry, CCEA/CEA GCE AS A2 Chemistry revising courses for pre-university students (equal to US grade 11 and grade 12 and AP Honours/honors level courses)

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