Dounreay PFR (Prototype Fast Reactor)
You may mean FBR - this stands for Fast Breeder Reactor
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.
See the India section of www.world-nuclear.org
Moderator is not used in case of fast breeder reactor because there is no need to slow down neutron energy. Nuclear fission takes place at high energy of neutrons.
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GEAR
The main disadvantage is the positive temperature coefficient of reactivity.
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Kalapakkam
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.