Classification of a nuclear reactor
A. Classification by type of nuclear reaction:
→ Thermal reactors: They use slow or thermal neutrons. Almost all current reactors are of this type. These contain neutron moderator materials that slow neutrons until their neutron temperature is thermalised.
→ Fast neutrons: They use fast neutrons to cause fission in their fuel. They do not have a neutron moderator, and use less moderating coolants.
→ Breeder reactors: They are capable of producing more fissile material than they consume during the fission chain reaction (by converting fertile U238 to Pu239, or Th232 to U233 ).
B. Classification by coolant:
Pressurised Water Reactors (PWR): These reactors use a pressure vessel to contain the nuclear fuel, control rods, moderator and coolant. They are cooled and moderated by high-pressure liquid water.
Boiling Water Reactors (BWR): A BWR is like a PWR without the steam generator. A boiling water reactor is cooled and moderated by water like a PWR, but at a lower pressure, which allows the water to boil inside the pressure vessel producing the steam that runs the turbines.
C. Classification by use:
Pressurised Heavy Water Reactor (PHWR): A Canadian design (known as CANDU), these reactors are heavy-water-cooled and -moderated pressurised water reactors. The fuel is contained in hundreds of pressure tubes. These reactors are fuelled with natural uranium and are thermal neutron reactor designs.
Gas Cooled Reactor (GCR) and Advanced Gas Cooled Reactor (AGR): These are generally graphite moderated and CO2 cooled.
Liquid Metal Fast Breeder Reactor (LMFBR): This is a reactor design that is cooled by liquid metal, totally unmoderated, and produces more fuel than it consumes. They are said to “breed” fuel, because they produce fissionable fuel during operation because of neutron capture.
Pebble Bed Reactors (PBR): These use fuel moulded into ceramic balls, and then circulate gas through the balls. The result is an efficient, low-maintenance, very safe reactor with inexpensive, standardised fuel.
Molten Salt Reactors: These dissolve the fuels in fluoride salts, or use fluoride salts for coolant. These have many safety features, high efficiency and a high power density suitable for vehicles.
Spacecraft propulsion: It is a method used to accelerate spacecraft and artificial satellites.
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