CANDU Reactors CANada Deuterium Uranium

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CANDU ReactorsCANada Deuterium Uranium

• Chal Davidson
• Kevin Kincaid

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Description

• Heavy water reactors are pressurized units that
  operating on the same basic conventions as most
  other PWRs
• The main difference is the use of deuterium as
  both
• A moderator
• And a coolant

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What Is Heavy Water?

• Heavy water (D2O) is a compound of an isotope of
  hydrogen called heavy hydrogen or deuterium (D)
  and oxygen
• Deuterium has an atomic mass of 2
• Heavy water has great similarity in its physical
  and chemical properties to ordinary water
• Heavy water is an excellent neutron moderator
• Heavy water is used as primary coolant to
  transport heat generated by the fission reaction
  to secondary coolant, light water

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System Design

• The control rods enter from the top and control
  the distribution of power in the reactor and can
  be used to shutdown the reactor
• Reactor's cooling water tubes are pressurized to
  1525 pounds per square inch, lower than
  pressurized water designs
• The heavy water in the moderator system is
  normally not highly pressurized
• Reactor cooling pumps circulate heavy water
  through the reactor then to the steam generators
  in a closed loop
• The moderator heavy water system has a separate
  heat exchanger with circulation system for
  cooling the moderator

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Integrated Use of Heavy Water and Light Water
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Reactor Vessel Assembly

• The CANDU reactor consists of the horizontal
  cylinder called the Calandria
• Fuel and coolant tubes run horizontally
• Moderator inlet and outlet tubes direct the
  moderator through the calandria, then to the
  external heat exchanger for cooling

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Fuel Uranium Dioxide

• The fuel assemblies used in the reactor
  are 1.5 feet (0.5
  m) long, consisting of
  individual rods
• Zircaloy cladding
• Fuel pellets consist of uranium dioxide
• Fuel burnup in a CANDU is 20 less than that
  obtained by many PWR and BWR reactors

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Refueling a Heavy Water Reactor

• PHWRs reactors can be refueled on-line. This
  photo shows the refueling machine. New fuel
  assemblies are added horizontally and the spent
  fuel assemblies are pushed out to the spent fuel
  storage area.

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Plant Layout
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Safety Systems

• Containment spray system
• Uses pumps to spray down the containment
• Containment fan coolers system
• Uses fan coolers with large radiators cooled by
  the ultimate heat sink
• Ice condensers
• Maintain large banks of borated ice stored in
  special baskets
• Reduces the size of the containment

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Safety Systems

• Vacuum building
• Maintained at a vacuum relative to the pressure
  in any of the reactor containments
• Pressure relief valves
• Open to direct the high pressure steam to the
  vacuum building which includes a spray system to
  reduce the pressure both within the affected
  reactor containment and the vacuum building

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Safety Systems
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Safety Systems

• Containment
• Double shell
• Access hatches for easy component replacement

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Location and Use of PHWRs

• Due to lower electrical power output this is a
  economical design for many smaller Nuclear
  Countries
• Country units Net MWe
• Argentina 3 1627
• Canada 22 15153
• China 2 1330
• India 14 3143
• Korea 4 1579
• Pakistan 1 125
• Romania 5 3185

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Questions?