1. Today’s Title: CW: fusion – our future?
01 December 2018
Today’s Title: CW: fusion – our future?
Learning Question: What is nuclear fusion?
Starter – what is happening at point 2?

2. Key words…
Fusion
Hydrogen
Helium
Isotopes
Validated
Peer-review
Electrostatic repulsion

3. Nuclear fusion
Nuclear fusion involves two atomic nuclei joining to make a large nucleus.
Energy is released when this happens.
Nuclear fusion can also be used as a source of energy.

4. Nuclear fusion
The Sun and other stars use nuclear fusion to release energy.
The sequence of nuclear fusion reactions in a star is complex, but overall hydrogen nuclei join to form helium nuclei.
Isotopes of hydrogen

5. Questions What is the source of energy in the Sun?
A: Nuclear fusion of hydrogen.
2. What are the products of the fusion reaction of hydrogen?
A: Helium and neutrons.

6. Getting new ideas accepted
New scientific theories have to be validated by the scientific community before they are accepted.
A report of the method and results is peer-reviewed (different scientists working in the same field check it)
Other scientists must be able to carry out the same experiment and get the same results

7. Fusion and temperature
Nuclear fusion involves a deuterium and a tritium nucleus colliding and being forced together.
Both nuclei are positively charged and therefore will repel each other.
This is known as electrostatic repulsion.

8. Fusion and temperature
The nuclei have to get very close in order to collide, which is approximately a million millionth of a millimetre.
If the nuclei are moving very fast then they can overcome the electrostatic repulsion.
The hotter a molecule is, the faster it will move and the more likely it is to collide.

9. Questions
3. Why does fusion not happen at room temperature? A: Hydrogen nuclei do not have enough energy to overcome the electrostatic force of repulsion. 4. Why does fusion happen at a lower temperature in the Sun than in a fusion reactor on Earth? A: The pressure is much greater in the Sun (so nuclei are closer together).

10. Fusion and temperature
For a nuclear fusion reactor to work, the temperature and pressure would each have to be very high.
These extremely high temperatures and pressures are very difficult to reproduce and are very expensive.
As a result, fusion as an energy source is a long way off.

11. Cold fusion
Scientists in 1989 claimed to have carried out nuclear fusion at 50oC – it was known as cold fusion
The scientific community has rejected their work as it cannot be validated (scientists tried and failed to get the same results when carrying out this experiment)

12. What are the differences between fusion and fission?
Nuclei split up in fission but join together in fusion;
while fusion does not create radioactive waste(but in both processes containment vessels become radioactive).
Fission
fission can take place at normal temperatures and pressures but fusion needs high temperatures and pressures;
fission creates radioactive waste from fuel

13. 6 Use scientific ideas to suggest why the idea of ‘cold fusion’ from Pons and Fleischmann’s results was not accepted.
A: Other scientists could not get the same results when they repeated the experiment.
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14. 7 Describe the difficulties of building a commercial fusion power station.
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15. Very difficult to sustain the high temperatures and pressures.
A: Very high temperatures and pressures are needed to overcome electrostatic forces of repulsion.
Very difficult to sustain the high temperatures and pressures.
So far none of the experimental reactors have produced more energy than was put in to heat up the hydrogen nuclei and contain them.
© Pearson Education Ltd Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original.