Nuclear Reactor is a system to initiate and control a sustained nuclear chain reaction. Reactors are used for generating electricity, moving aircraft carriers and submarines, producing medical isotopes for imaging and cancer treatment, and for conducting research. Just as conventional power stations generate electricity by harnessing the thermal energy released from burning fossil fuels, nuclear reactors convert the thermal energy released from nuclear fission.

Components of Nuclear Reactor Design

  • Nuclear Fuels. Uranium is the basic fuel. Usually pellets of uranium oxide (UO2) are arranged in tubes to form fuel rods. The rods are arranged into fuel assemblies in the reactor core.
  • Moderator. This is material in the core which slows down the neutrons released from fission so that they cause more fission. It is usually water, but may be heavy water or graphite.
  • Control rods. These are made with neutron-absorbing material such as cadmium, hafnium or boron, and are inserted or withdrawn from the core to control the rate of reaction, or to halt it.
  • Nuclear Steam Turbine. Turbine transfers the heat from the coolant to electricity, just like in a fossil-fuel plant.
  • Nuclear Reactor Coolant. A liquid or gas circulating through the core so as to transfer the heat from it. In light water reactors the water moderator functions also as primary coolant. Except in BWRs, there is secondary coolant circuit where the steam is made.
  • Pressure vessel or pressure tubes. Usually a robust steel vessel containing the reactor core and moderator/coolant, but it may be a series of tubes holding the fuel and conveying the coolant through the moderator.
  • Steam generator. (not in BWR) Part of the cooling system where the primary coolant bringing heat from the reactor is used to make steam for the turbine. Reactors may have up to four “loops”, each with a steam generator.
  • Containment. The structure around the reactor core which is designed to protect it from outside intrusion and to protect those outside from the effects of radiation in case of any malfunction inside. It is typically a metre-thick concrete and steel structure.

Nuclear Reactor Types & Technologies

  • Nuclear Fission Reactors – All commercial power reactors are based on nuclear fission. They generally use uranium and its product plutonium as nuclear fuel, though a thorium fuel cycle is also possible.
    • Nuclear Thermal Reactors use slowed or thermal neutrons.
      • Nuclear Graphite Moderated Reactors
      • Water Moderated Nuclear Reactors
        • Heavy Water Reactor (HWR)
          • Pressurized water reactor (PWR)
          • Pressurized Heavy Water Reactor (PHWR)
          • Boiling Water Reactor (BWR)
        • Light Water Reactors (LWR) – Light water reactors use ordinary water to moderate and cool the reactors.
      • Light Element Moderated Reactors – These reactors are moderated by lithium or beryllium.
        • Molten Salt Reactors (MSR) are moderated by a light elements such as lithium or beryllium, and cooled by circulating a molten salt, typically a eutectic mixture of fluoride salts
        • Liquid metal cooled reactors, such as one whose coolant is a mixture of Lead and Bismuth
          • Sodium-cooled fast reactor
          • Lead-cooled fast reactor
        • Gas cooled reactors are cooled by a circulating inert gas, often helium in high-temperature designs
      • Organically Moderated Reactors (OMR) use biphenyl and terphenyl as moderator and coolant.
    • Fast neutron reactors use fast neutrons to cause fission in their fuel.
  • Nuclear Fusion Reactors – Fusion power is an experimental technology, generally with hydrogen as fuel. While not suitable for power production, Farnsworth-Hirsch fusors are used to produce neutron radiation.