Question

The function of a moderator in a nuclear reactor is?
1. To moderate the number of secondary nuclei
2. To control the fission reaction
3. To increase the number of fissile (or fissionable) nuclei
4. To slow down the secondary neutrons

Answer 1

Correct Answer - Option 4 : To slow down the secondary neutrons

The correct answer is To slow down the secondary neutrons.

• The moderator helps slow down the neutrons produced by fission to sustain the chain reaction.
  • Control rods can then be inserted into the reactor core to reduce the reaction rate or withdrawn to increase it.
  • ​A moderator is used to slow down the high energy neutrons upto the thermal neutrons, having energy 0.025 eV, emitted in the chain reaction of U235   fission.
    • Generally, graphite is used as a moderator in nuclear power plants.

• Nuclear reactor
  • A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions.
  • Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion.
• Light Water Reactor
  • The light-water reactor is a type of thermal- neutron reactor that utilizes normal water as opposed to heavy water.
  • It is fuelled by Low Enriched Uranium.
  • It uses water as both a coolant method and a neutron moderator.
  • It produces heat by controlled nuclear fission.
• Pressurized Heavy Water Reactor
  • PHWR is a nuclear power reactor, commonly using unenriched natural uranium as its fuel.
    • It uses heavy water (Deuterium oxide D_²O) as its coolant and moderator.
  • The heavy water coolant is kept under pressure, allowing it to be heated to higher temperatures without boiling, much as in a typical pressurized water reactor.
  • While heavy water is significantly more expensive than ordinary light water, it yields greatly enhanced neutron economy, allowing the reactor to operate without fuel enrichment facilities.

• Presently, India has 22 operating nuclear power reactors, with an installed capacity of 6780 MegaWatt electric (MWe).
  • Among these eighteen reactors are Pressurised Heavy Water Reactors (PHWRs) and four are Light Water Reactors (LWRs).
    • The nuclear energy programme in India was launched around the time of independence under the leadership of Homi J Bhabha.