1. Building a CANDU reactor

2. Nuclear Reaction Review
Uranium has a large nucleus which is barely stable
The addition of another subatomic particle into the nucleus can force the nucleus to become unstable
The unstable nucleus fissions (or splits) to form two new substances called daughter nuclei.

4. 3 energetic neutrons are also ejected from the average reaction
3 energetic neutrons are also ejected from the average reaction. These energetic neutrons are called fast neutrons
The two daughter nuclei have less binding energy then the Uranium. This difference in energy is seen as heat energy.

5. Fissioning of Uranium (enriched)
1n U U Ba Kr n MeV

6. Power Plant requirements
A method to slow energetic neutrons so they can react with Uranium nucleus
A method to limit the number of neutrons that react in the chain reaction
A method to absorb the heat energy to convert the heat into electricity
Safety protocols to stop the nuclear reaction

7. The nuclear reaction
The nuclear reaction occurs inside the fuel channel assembly.
This assembly has to be bathed in some material to slow the energetic neutrons.

8. The moderator
Moderator is the substance which slows the energetic neutrons but does not absorb them
Heavy water is the ideal candidate

9. Heavy water is a molecule in which the hydrogen contains a neutron
The heavy water is heavier than normal (light) water

10. The increase in density of the heavy water allows for more collisions with the neutrons.
These increased number of collisions absorbs enough energy to turn the fast neutrons into slow neutrons … which can react with the uranium.

11. Controlling the reaction
If the three created neutrons were allowed to react the reaction would increase exponentially
This is the model for the atomic bomb
Ideally only one of the three neutrons would be allowed to react with the Uranium
Two of the created neutrons must be absorbed

12. Control Rods
Rods of Cadmium metal can be inserted into the reactor chamber to absorb neutrons
If the rods are fully inserted the reaction completely shuts down

13. CANDU steam loop

14. The heavy water moderator turns to steam as it absorbs the energy of the nuclear reaction
This steam is pumped through a condenser loop in which thermal energy is absorbed by light water
The light water steam is used to drive a steam turbine which converts steam into electricity

15. Safety
In the event of a power loss, control rods drop into the reactor stopping the reaction
The liquid heavy water moderator can be removed quickly … stopping the reaction

16. The reactor core is a closed system
The reactor core is a closed system. The radiated heavy water never comes into contact with the light water from the lake.
A liquid “poison” can be added to the moderator absorbing the neutrons shutting the reaction down

17. The next slide shows a schematic of a typical CANDU reactor
The next slide shows a schematic of a typical CANDU reactor. Use the schematic to write a short summary of the operation of the reactor.