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(c) doc b(c) doc bDoc Brown's Chemistry KS4 science GCSE/IGCSE/AS Physics Revision Notes

9. Nuclear Fission Reactions - nuclear power energy resource

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What exactly is 'nuclear power'? What is a nuclear reactor? What is nuclear fission? What processes go on that release so much energy in nuclear fission? What is a chain reaction? What does a moderator do in a nuclear reactor? Why are uranium-235 and plutonium good nuclear fuels?

Radioactivity & nuclear physics Index 1a. The Structure of Atoms - 3 fundamental particles * 1b. What it is an atom like? * 2a. What is Radioactivity? Why does it happen? * 2b. How did they find out there were three types of atomic-ionising radiation? * 3a. Detection of Radioactivity and its measurement, units * 3b. Ionising Radiation sources * 4a. The properties of the three types of radioactive emission and symbols * 4b The dangers of radioactive emissions - beware of ionising radiation from radio-isotopes! * 5. The uses of radioactive Isotopes emitting alpha, beta or gamma radiation * 6a. The half-life of a radioisotope - how long does material remain radioactive? implications! * 6b. Uses of decay data and half-life values * 7a. What actually happens to the nucleus in alpha and beta radioactive decay? nuclear equations! * 7b. The production of Radioisotopes - artificial sources * 8. Nuclear fusion reactions and the formation of 'heavy elements' * 9. Nuclear Fission Reactions, nuclear power energy resource

 

9. Nuclear Fission Reactions, nuclear power energy resource

  • 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!

  • (c) doc bThis 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!) ...

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uranium splits into lanthanum and bromine nuclei

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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

Advanced Chemistry Page Index and Links

(c) doc b(c) doc bRADIOACTIVITY multiple choice QUIZZES and WORKSHEETS

Easier-Foundation Radioactivity Quiz

or Harder-Higher Radioactivity Quiz

 (c) doc b five word-fills on radioactivity * Q2 * Q3 * Q4 * Q5and ANSWERS!

crossword puzzle on radioactivity and ANSWERS!


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