30 April, 2007

Nuclear Energy,Nuclear Fuels

Nuclei are made up of protons and neutron, but the mass of a nucleus is always less than the sum of the individual masses of the protons and neutrons which constitute it. The difference is a measure of the nuclear binding energy which holds the nucleus together.

Nuclear energy is energy released from the atomic nucleus. Atoms are tiny particles that make up every object in the universe. There is enormous energy in the bonds that hold atoms together.This binding energy can be calculated from the Einstein relationship: mass-energy equivalence formula E = mc², in which E = energy, m = mass, and c = the speed of light in a vacuum (a physical constant).The alpha particle gives binding energy of 28.3 MeV
Nuclear energy is released by several processes:
  • Radioactive decay, where a radioactive nucleus decays spontaneously into a lighter nucleus by emitting a particle;
  • Endothermic nuclear reactions where two nuclei merge to produce two different nuclei. The following two processes are particular examples:
  • Fusion, two atomic nuclei fuse together to form a heavier nucleus;
  • Fission, the breaking of a heavy nucleus into two nearly equal parts.
Nuclear Fuels
Nuclear fuel is any material that can be consumed to derive nuclear energy, by analogy to chemical fuel that is burned to derive energy. By far the most common type of nuclear fuel is heavy fissile elements that can be made to undergo nuclear fission chain reactions in a nuclear fission reactor; nuclear fuel can refer to the material or to physical objects (for example fuel bundles composed of fuel rods) composed of the fuel material, perhaps mixed with structural, neutron moderating, or neutron reflecting materials.
Not all nuclear fuels are used in fission chain reactions. For example, 238Pu and some other elements are used to produce small amounts of nuclear power by radioactive decay in radiothermal generators, and other atomic batteries. Light isotopes such as 3H (tritium) are used as fuel for nuclear fusion. If one looks at binding energy of specific isotopes, there can be an energy gain from fusing most elements with a lower atomic number than iron, and fissioning isotopes with a higher atomic number than iron.
The most common fissile nuclear fuels are natural urnium,enriched uranium,plutonium and 233U.Natural uranium is the parent material.The materials 235U,233U and 239Pu are called fissionable materials.The only fissionable nuclear fuel occuring in nature is uraium of which 99.3% is 238U and 0.7% is 235U and 234U is only a trace.Out of these isotopes only 235U will fission in a chain reaction.The other two fissionable materials can be produced artificially from 238U and 232Th which occur in nature are called fertile materials.Out of the three fissionable materials 235U has some advantages over the other two due to its higher fission percentage.Fissionable materials 239Pu and 233U are formed in the nuclear reactors during fission process from 238U and 232Th respectively due to absorption of neutrons with out fission.Getting 239Pu process is called conversion and getting 233U is called breeding.

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