CANDU Reactor Power Plant

A reactor developed and designed by Canadian is called as CANDU (CANadian Deutorium Uranium ) reactor.
It uses pressurized heavy water (which has 99.8% deutorium oxide ) as moderator and primary coolant. Natural Uranium is used as fuel for this reactor.
A Canadian Deutorium Uranium Pressurized Heavy Water power plant is shown in figure.
CANDU Reactor Power Plant | enggarena.net
CANDU Reactor Power Plant

Natural uranium used as fuel is in the form of small cylinder palletes. These are packed in corrosion resistant Zirconium alloy tubes of 0.5 cm long and 1.3 cm in diameter to form a fuel rod.
These short rods are combined in 37 bundles of 37 rods and 12 bundles are placed end to end in each pressure tubes.
This type of arrangement helps in refuelling the reactor while in operation.
Reactor vessel is a cylinder called Calandria.It is placed horizontally . It has pressure tubes penetrating the reactor vessel. The active core is about 6 m high abd 7-8 m diameter.
In the primary circuit deutorium coolant enters the array of pressure tubes at 110 bar pressure and 260 degree Celsius temperature. It flows through the fuel element and leaves the pressure tubes at about 370 degree Celsius after absorbing the heat generated by fission of fuel material.
The coolant at 110 bar and 370 degree leaving the reactor enters the steam power plant where the generated steam is used in conventional steam power plant.
Control rods are made up of cadmium. These control rods are used to start and shut down the reactor. In addition, there are other absorbing rods which are used to control the power output during reactor operation.

Advantages of CANDU Reactor :

1. Enriched fuel is not required.
2. Cost and time of construction is less.
3. It has good neutron economy resulting into good breeding ratio.
4. Heavy water is used as moderator which has low fuel consumption.

Disadvantages of CANDU Reactor :

1. Heavy water used as moderator is costly.
2. Leakage problem may occur.
3. It has critical temperature limitations.
4. It requires has standard of design, manufacture and maintenance.
5. Size of plant is large.
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Sujit Kadus

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