Nuclear fission reactors

There has been much investment in different types of reactor, whether to exploit different fuels, or the new generation of reactors, employing new technologies which were previously unknown or considered impracticable.

Reactor Generations

Generation IV nuclear reactors are expected to be in operation in the 2030s. They offer improvements in economic viability, safety, waste reduction and are more proliferation resistant. Most reactors in operation today are 2nd generation. Generation I reactors were the early prototypes built in the 1950s and 60s.

Generation II: these are the majority of commercial power reactors, and include LWR, PWR, BWR, CANDU, WER/RMBK.
  • PWR = pressurised water reactor
  • LWR = light-water reactor
  • BWR = boiling water reactor
  • CANDU = CANada Deuterium Uranium
  • RMBK = Reaktor Bolshoy Moshchnosti Kanalnyy (High Power Channel-type Reactor)

Generation III: these reactors were introduced from the mid-1990s till 2010. They include advanced LWRs, ABWR, System SO+, APeco, and EPR. Generation III+ reactors are currently being employed, and are evolutionary in design, offering better ROI.

  • ABWR = Advanced Boiling Water Reactor
  • EPR = Evolutionary Power Reactor

Generation IV Reactors:

  • VHTR = very high temperature reactor
  • MSR = molten salt reactor
  • SSR = stable salt reactor
  • SCRW = supercritical water reactor
  • GFR = gas-cooled fast reactor
  • SFR = sodium-cooled fast reactor
  • LFR = lead-cooled fast reactor


The Clean And Environmentally Safe Advanced Reactor, CAESAR, is a design still in development, which proposes to utilise an initial quantity of LEU (low-enriched uranium) to start the reactor, which will then continue with only U-238 as fuel. Neutrons will be controlled by means of a steam moderator.


Advanced Heavy Water Reactor, whose development may include thorium-based fuel cycles by the 2040’s.

One of the three cores in the US Shippingport Atomic Power Station was a 60MWe thorium breeder reactor. It operated from 1977 till 1982, when the experimental core was removed, to reveal that the quantity of fissile material had actually increased by 1.4%, demonstrating the effectiveness of the breeding system. It used pellets made up of a combination of thorium dioxide and uranium-233 oxide.