1. Nuclear Fission - Review

2. Fission
The Uranium 236 is very unstable and splits into two smaller nuclei (this is called nuclear fission)

3. Chain Reaction
If there is enough uranium (critical mass) a chain reaction occurs. Huge amounts of energy are released very quickly.
                                                                 
                                                                 

4. Bang!
This can result in a nuclear explosion!

5. Controlled fission
The chain reaction can be controlled using control rods and a moderator. The energy can then be used (normally to generate electricity).

6. Moderator
This slows the free neutrons down, making them easier to absorb by the uranium 235 nuclei. Graphite or water is normally used.
1 eV neutrons are ideal)

7. Control rods
These absorb excess neutrons,making sure that the reaction does not get out of control. Boron is normally used.

8. Heat
The moderator gets hot from the energy it absorbs from the neutrons.

9. Heat
This heat is used to heat water, to make steam, which turns a turbine, which turns a generator, which makes electricity.

10. Useful by-products
Uranium 238 can also absorb neutrons to produce plutonium 239 which is itself is highly useful as a nuclear fuel.

11. Nuclear Power
That’s how a nuclear power station works!

12. Nuclear power - Advantages
High power output
Large reserves of nuclear fuels
No greenhouse gases

13. Nuclear power - disadvantages
Waste products dangerous and difficult to dispose of
Major health hazard if there is an accident
Problems associated with uranium mining
Nuclear weapons

14. Solar power

15. The solar constant

16. The solar constant
The sun’s total power output is 3.9 x 1026 W!

17. I is the power per unit area
The solar constant
The sun’s total power output is 3.9 x 1026 W!
Only a fraction of this power actually reaches the earth, given by the formula I = P/4πr2
I is the power per unit area
For the Earth this is 1400 W.m-2 and is called the solar constant
This varies according to the power output of the sun (± 1.5%), distance from sun (± 4%), and angle of earth’s surface (tilt)

18. Solar power - advantages
“Free”
Renewable
Clean

19. Solar power - disadvantages
Only works during the day
Affected by cloudy weather
Requires large areas
Initial costs are high
Difficult to scale

20. Hydroelectric power

21. Water storage in lakes
“High” water has GPE. As it falls this turns to KE, turns a turbine etc.

22. Pumped storage
Excess electricity can be used to pump water up into a reservoir. It acts like a giant battery.

23. Tidal water storage
Tide trapped behind a tidal barrage. Water turns turbine etc.

24. Hydroelectric - Advantages
“Free”
Renewable
Clean

25. Hydroelectric - disadvantages
Very dependent on location
Drastic changes to environment (flooding)
Initial costs very high

26. Wind power

27. Wind power
Calculating power

28. Wind moving at speed v, cross sectional area of turbines = A
A Cylinder of Air A

29. Wind moving at speed v, cross sectional area of turbines = A
Volume of air going through per second = Av
Mass of air per second
= Density x volume
Mass of air per second = ρAv V A

30. Wind moving at speed v, cross sectional area of turbines = A
Mass of air per second = ρAv
If all kinetic energy of air is transformed by the turbine, the amount of energy produced per second = ½mv2 = ½ρAv3 V A

31. Wind power - advantages
“Free”
Renewable
Clean
Ideal for remote locations

32. Wind power - disadvantages
Works only if there is wind!
Low power output
Unsightly (?) and noisy
Best located far from cities
High maintainance costs

33. Wave power

34. OWC
Oscillating water column

35. Power per unit length
A water wave of amplitude A carries an amount of power per unit length of its wavefront equal to P/L = (ρgA2v)/2 where ρ is the density of water and v stands for the speed of energy transfer of the wave

36. Wave power - Advantages
“Free”
Reasonable energy density
Renewable
Clean

37. Wave power - disadvantages
Only in areas with large waves
Waves are irregular
Low frequency waves with high frequency turbine motion
Maintainance and installation costs high
Transporting power
Must withstand storms/hurricanes