The moderator is used to slow down the neutrons present in the core of the reactor. Normally the neutrons produced as the nuclear fuel (e.g. uranium) is fissioned are travelling too fast to produce a sustained chain reaction. Some examples of moderators are cadmium, heavy water and graphite.
Uranium. There is some interest in using thorium in the future. Thorium cannot be used directly as fuel in a reactor as it does not fission, it requires a fast breeder reactor to convert it to Uranium-233 which does fission.
Graphite rods are used as moderators in a nuclear reactor with natural uranium. Graphite slows down the fast neutrons released during fission reactions, allowing them to cause further reactions and sustain the chain reaction. This is necessary because natural uranium is not as efficient at sustaining a chain reaction without a moderator.
Uranium. A breeder reactor can use either Uranium, Plutonium, or mixed Transuranic elements for fuel. Depleted Uranium or Thorium is used as the breeding blanket. Periodically the breeding blanket is changed: the old one reprocessed to make new fuel.
Heavy water (deuterium) functions as a moderator. It slows down fast neutrons released by fission reactions in order to allow the reaction to be sustained. Fast neutrons pass through the reactor before initiating another fission reaction.
No, a breeder nuclear reactor does not typically use a moderator. Breeder reactors are designed to produce more fissile material than they consume by using fast neutrons to convert non-fissile isotopes into fissile ones without slowing down the neutrons.
Moderators are not used in a breeder reactor because their primary purpose is to slow down neutrons to increase the likelihood of fission events in a thermal reactor. In a breeder reactor, fast neutrons are required to convert non-fissile uranium-238 into fissile plutonium-239, so using a moderator would hinder this process.
Kalpakkam has both Thermal reactor (Madras Atomic Power Station) and Fast Breeder Reactor -FBTR and PFBR (Under construction). In MAPS (thermal reactor) it is Heavy Water (D2O) Which acts as a coolant as well as moderator, where as in Fast Breeder Test Reactor (FBTR) and Prototype Fast Breeder Reactor (PFBR) Sodium (Na) is used as coolant. Since there should not any moderators for fast reactors D2O will not be used as coolant in fast reactors.
You may mean FBR - this stands for Fast Breeder Reactor
Dounreay PFR (Prototype Fast Reactor)
Yes, they are fast nuclear reactors
See the India section of www.world-nuclear.org
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GEAR
The main disadvantage is the positive temperature coefficient of reactivity.
The moderator is used to slow down the neutrons present in the core of the reactor. Normally the neutrons produced as the nuclear fuel (e.g. uranium) is fissioned are travelling too fast to produce a sustained chain reaction. Some examples of moderators are cadmium, heavy water and graphite.
Kalpakkam