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Nuclear fission and fusion
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Splitting heavy nuclei or joining light ones releases huge amounts of energy. Separate Physics only.
Fission
A uranium-235 nucleus absorbs a neutron, becomes unstable and splits into two smaller nuclei, releasing 2 or 3 neutrons and energy.
Those neutrons can cause more fissions: a chain reaction.
Those neutrons can cause more fissions: a chain reaction.
Nuclear reactors
Control rods (boron) absorb neutrons to control the rate.
The moderator (graphite or water) slows neutrons so they cause fission.
Shielding (thick concrete) stops radiation escaping.
The moderator (graphite or water) slows neutrons so they cause fission.
Shielding (thick concrete) stops radiation escaping.
Fusion
Two light nuclei (such as hydrogen isotopes) join to make a heavier nucleus, releasing energy. This powers stars.
Fusion needs extremely high temperature and pressure to overcome the repulsion between positive nuclei, which is why it is hard to achieve on Earth.
Fusion needs extremely high temperature and pressure to overcome the repulsion between positive nuclei, which is why it is hard to achieve on Earth.
What is the purpose of control rods in a reactor?
- They absorb neutrons.
- This controls how many fissions happen, so the chain reaction does not run out of control.
Answer: To absorb neutrons and control the rate.
Fission: U-235 absorbs a neutron and splits, releasing neutrons for a chain reaction. Control rods absorb neutrons; the moderator slows them. Fusion joins light nuclei and needs huge temperatures.
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