Section 1 of 7Where the waste comes from
Fission products
- Fission products When a nucleus of uranium-235 or plutonium-239 splits, it forms two smaller daughter nuclei.
- These fission products are usually unstable and therefore radioactive.
- Their activity is often greater than that of the original fuel.
Spent fuel rods
- Spent fuel rods After a period in the reactor the fuel rods contain so many fission products that they can no longer sustain an efficient chain reaction.
- These spent rods are removed and replaced, but they are still intensely radioactive and very hot.
Small volume, high danger
- Small volume, high danger Compared with the huge amount of energy generated, the quantity of waste is small.
- However, it is extremely hazardous, so the volume produced does not tell you how risky it is.
Section 2 of 7Why the waste is such a problem
1Unstable daughter nuclei
- Unstable daughter nuclei Fission produces nuclei with the wrong balance of protons and neutrons, so they emit radiation.
2Long half-lives
- Long half-lives Some products have half-lives of thousands of years, so their activity falls very slowly.
3Long-term hazard
- Long-term hazard The waste stays dangerous to living cells for an extremely long time, so it must be isolated for thousands of years.
4Storage decisions
- Storage decisions This is the biggest drawback of nuclear power and strongly affects whether countries choose to use it.
Section 3 of 7Handling and storing waste
1
Spent fuel rods are removed from the reactor using remote handling equipment, because they give out harmful radiation and a lot of heat.
2
They are cooled first, usually in deep water ponds, which absorb radiation and carry away the heat.
3
The most dangerous waste is sealed in strong, corrosion-resistant containers so that no radioactive material can escape.
4
The containers are buried deep underground in stable rock, away from groundwater and from people.
5
The site is monitored and kept secure until the radioactivity has fallen to a level that is no longer harmful.
Section 4 of 7Case study: Chernobyl, 1986
| Aspect | What happened |
|---|---|
| Location | Chernobyl nuclear power plant in Ukraine. |
| Cause | During a safety test the control rods were removed, so the reaction could no longer be controlled and an explosion occurred. |
| Release | A very large amount of radioactive material was thrown into the air and spread over the surrounding region. |
| Human response | Hundreds of thousands of people were evacuated to avoid contamination. |
| Lasting effect | An exclusion zone of about 2600 km2 is still in place because radiation levels there remain high. |
Section 5 of 7Weighing up nuclear power
Advantages
- Advantages A small mass of fuel releases a very large amount of energy.
- No carbon dioxide is released when the reactor is running.
Disadvantages
- Disadvantages Radioactive waste must be stored safely for thousands of years.
- Accidents are rare but can have severe, long-lasting effects on people and land.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Fission products | The smaller, usually radioactive, nuclei produced when a heavy nucleus splits. |
| Spent fuel rod | A fuel rod that has been used in a reactor and is full of radioactive fission products. |
| Half-life | The time taken for the activity of a radioactive sample to fall to half its starting value. |
| Daughter nuclei | The new nuclei formed when a parent nucleus undergoes fission or decay. |
| Exclusion zone | An area around a hazard that people are not allowed to live in or enter because of danger. |
| Contamination | The unwanted presence of radioactive material on or inside objects or people. |
Section 7 of 7Exam technique
1
Saying that nuclear power stations produce a lot of waste. The volume is small; the problem is that it stays dangerous for a very long time.
2
Thinking waste is dangerous only because it is hot. Radiation from the fission products is the main hazard, and the heat is an extra problem for spent fuel rods.
3
Claiming the waste can be made safe quickly. Its activity falls only as the long half-lives allow, so it needs isolating for thousands of years.
4
Stating that Chernobyl was caused by an earthquake or a leak. It happened during a safety test when the control rods were removed.
5
Confusing fission products with the fuel. The products are the smaller nuclei formed after the uranium or plutonium nucleus splits.