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Idealized Thermal Nuclear Reactor

Essay by Andrew Keenleyside  •  February 18, 2018  •  Coursework  •  348 Words (2 Pages)  •  339 Views

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Idealized Thermal Nuclear Reactor

Fuel Rods:

  • Fuel in form of small pellets
  • Pellets held in bundles and several bundles make up fuel rod

Control Rods:

  • Moveable pieces of neutron-absorbing material
  • Used to control reactivity k of reactor
  • CANDU reactors use light water in control rods
  • Fine tuning of reactivity done with stainless steel neutron flux adjuster rods


  • Slows fission neutrons to an energy where fission cross section of fuel high enough to guarantee k > 1

Neutron Reflector:

  • Layer of neutron-moderating material surrounding the reactor core which causes fast neutrons emitted from core to undergo elastic scattering with some being reflected back into core
  • CANDU reactors: D2O moderator surrounding core acts as a neutron reflector
  • Greatly increases efficiency

Reactor Vessel:

  • Outer boundary of reactor core
  • CANDU reactors the calandria vessel is very big but isn’t exposed to high temp or pressure

Nuclear Reactor Fuels

Fissile Material:

  • Material which undergoes fission when hit with low energy thermal neutrons

Fertile Material:

  • Material that doesn’t undergo fission within a nuclear reactor however it absorbs neutrons and decays into new isotopes which are fissile

Light Water Reactors

  • Use H2O as coolant and moderator
  • Must use enriched uranium because H2O moderator absorbs too many neutrons to allow natural uranium to be used as fuel
  • Thermal efficiency of 30-33%

Gas-Cooled Reactors

  • Cooled with either CO2 or Helium (He) gas (not strong neutron absorbers)
  • Moderated with graphite
  • Most thermal efficient up to 50%!

Breeder Reactors

  • Most efficient breeder reactors use Fast neutrons to accomplish the fission process
  • Use 233U as fuel
  • For molten salt breeder reactor, the salt solution is piped through a graphite moderated core
  • No control rods in core
  • k value controlled by flow rate of molten salt through the core
  • inherently low efficiency but have high thermal efficiency (44%)

CANDU Reactor

  • PWR reactor
  • Pressure tubes are pressurized through the calandria
  • UO2 fuel pellets are in tubes and pressurized D2O coolant runs through the tubes and carries away the fission heat
  • Room temperature D2O fills spaces between pressure tubes in calandria and acts as primary moderator and neutron reflector of reactor core



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