Splitting heavy, joining light

Science · Matter & Materials · ages 15-16

Name ______________________ Date ____________

What do control rods do in a reactor?
- Speed up neutrons
- Soak up spare neutrons to steady the rate
- Cool the building air
What happens in fission?
- A heavy nucleus splits into two lighter ones plus neutrons
- Light nuclei join into heavier ones
- Electrons jump between levels
What joins in fusion?
- Heavy uranium nuclei
- Lead blocks
- Light nuclei like hydrogen
Rods are pushed deeper into a running reactor. What happens to power?
- It rises
- It falls
- It stays exactly flat
Why does fusion need enormous temperature and pressure?
- Hydrogen is too cold to burn
- Both nuclei are positive and repel each other
- Magnets stop working otherwise
Which waste picture is right?
- Fission leaves long lived waste, fusion far shorter lived
- Both leave no waste at all
- Fusion leaves the longer lived waste
Why does fission run power stations today while fusion does not?
- Fission fuel is free
- Fusion releases no energy
- Fission chains sustain themselves at ordinary pressures, fusion needs a star's conditions
Fusion already powers most national grids.
Circle one: True False

Answer key

For grown-ups. Fold this page away before handing over the rest.

Soak up spare neutrons to steady the rate · Rods drink in neutrons: in to calm, out to raise power.
A heavy nucleus splits into two lighter ones plus neutrons · Fission breaks a heavy nucleus after it swallows a neutron.
Light nuclei like hydrogen · Fusion builds heavier nuclei from light ones.
It falls · More rod in means more neutrons soaked up.
Both nuclei are positive and repel each other · Only extreme speed and squeeze beat the repulsion.
Fission leaves long lived waste, fusion far shorter lived · Split fragments must be stored for centuries.
Fission chains sustain themselves at ordinary pressures, fusion needs a star's conditions · Practicality decides: one sustains itself, the other needs caging a star.
False · Fusion lights the Sun, but station scale engineering is still being cracked.