Nuclear Power

这是一篇关于Nuclear Power的思维导图，《Nuclear Power》是一本图书，作者是National Research Council; Committee on Future Nuclear Power Develo; Energy Engineering Board

Nuclear Power

• What is nuclear power? What are the scientific principles behind it?
  • Nuclear power is the controlled use of nuclear energy.
  • 4 types of nuclear reaction
    • Radioactive decay
      • some chemical elements have atoms that change over time.
        • alpha decay(He)
          • Alpha decay causes the nucleus to lose two protons and two neutrons. Also it causes the atom to change into another element, because the atom loses two protons (and two neutrons).
          • The alpha particle can't go though your skin even a few centimeter of air so it is save. But when it comes into your body, it will be very dangerous.
        • beta decay(electric current)
          • beta-plus
            • the nucleus gives out a negatively charged electron and a neutron changes into a proton
          • beta-minus
            • the nucleus releases a positron, which is like an electron but it is positively charged, and a proton changes into a neutron
          • Beta rays are more penetrating than alpha rays, but cause less damage over the same distance.Some beta rays can penetrate the skin and cause radiological damage.But it can do even more damage once in the body.Beta particles can be removed, blocked by external clothing or completely blocked by a sheet of aluminum foil a few millimeters thick
        • gamma decay(electromagnetic wave)
          • Gamma decay happens when a nucleus produces a high-energy packet of energy called a gamma ray
          • gamma ray is not only useful but also very dangerous
        • These various kinds of decay can happen sequentially in a "decay chain". One kind of nucleus decays to another kind, which decays again to another and so on until it becomes a stable isotope and the chain comes to an end.
      • making nuclear battery
        • for sattelite/plantary probe
    • Nuclear fusion
      • Nuclear fusion is the process of making a single heavy nucleus (part of an atom) from two lighter nuclei
        • The nucleus made by fusion is heavier than either of the starting nuclei. However, it is not as heavy as the combination of the original mass of the starting nuclei (atoms). This lost mass is changed into lots of energy. This is shown in Einstein's famous E=mc2 equation.
      • At present, it hasn't been put into commercial use, but scientists are now trying their best to make it come true
    • Nuclear fission
      • Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radioactive decay.
      • It has been put in use for commerce and science
    • artificial
• How does it produce electricity?
  • Nuclear energy can be released by nuclear reactions in a machine called a nuclear reactor. This energy boils water for a steam engine to make electricity, which then can be used to power machines and homes.
    • Pressurized Water Reactor(PWR)
      • In a PWR, the primary coolant (water) is pumped under high pressure to the reactor core where it is heated by the energy released by the fission of atoms. The heated, high pressure water then flows to a steam generator, where it transfers its thermal energy to lower pressure water of a secondary system where steam is generated. The steam then drives turbines, which spin an electric generator.
        • coolant
          • Light water is used as the primary coolant in a PWR.
        • Moderator
          • In PWRs the coolant water is used as a moderator by letting the neutrons undergo multiple collisions with light hydrogen atoms in the water, losing speed in the process
        • fuel
          • the uranium dioxide (UO2) powder(it is fired to create hard, ceramic pellets of enriched uranium dioxide. And then , the pellets is clad into a special metal pipe which is filled with helium
      • advantages
        • stable due to their tendency to produce less power as temperatures increase
        • turbine cycle loop is separate from the primary loop, so the water in the secondary loop is not contaminated by radioactive materials.
        • safe. The control rods are held by electromagnets and fall by gravity when current is lost full insertion safely shuts down the primary nuclear reaction
      • disadvantages
        • The coolant water must be highly pressurized to remain liquid at high temperatures. This requires high strength piping and a heavy pressure vessel and hence increases construction costs.
        • Natural uranium is only 0.7% uranium-235, the isotope necessary for thermal reactors. This makes it necessary to enrich the uranium fuel, which significantly increases the costs of fuel production.
    • boiling water reactor
      • A boiling water reactor uses demineralized water as a coolant and neutron moderator. Heat is produced by nuclear fission in the reactor core, and this causes the cooling water to boil, producing steam. The steam is directly used to drive a turbine, after which it is cooled in a condenser and converted back to liquid water.
        • coolant
        • moderator
        • fuel
        • the same as the PWR
      • advantages
        • easy to operate
          • since the system is simple
        • the devices don't need changing so often
          • the pressure is much more smaller
      • disadvantages
        • danger
          • Control rods are inserted from below for current BWR designs
    • light water reactor
    • HeavyWaterReactor
    • fast neutron reactor
    • ............
• Is it a safe form of energy? What is good and what is bad?
  • the nuclear power now is a quite safe energy. If it is used properly there will be nearly no safety problems.
  • advantages
    • the energy it can provide is clean , huge and efficient. The nuclear fuel is also very abundance. Planty of the scientific research need the nuclear reactor and energy.
  • disadvantages
    • Once the accident happened, the influence of the radiation might last for centuries or even thousands of years.
• Are there any other contexts associated with nuclear power that are worth exploring?
  • the solution of dealing with Nuclear waste water
    • 1chemical precipitation method
      • Most compounds are insoluble. Using this method can reduce most harmful compounds
      • ion exchange method
        • it reduce the radiational matters in the water further
    • 3adsorption method
      • An effective method for removing heavy metal from water
    • 4evaporation and concentration
      • It concentrates matter and prepare for solidification
    • 5membrane separation technique
      • Use membrane to separate pure water and other material