Section 1 of 5Energy Changes
Starting point
- The energy in the fuel is stored in the nuclei of uranium-235 or plutonium-239.
Fission
- In fission this energy is transferred to the kinetic energy of the fission fragments and neutrons.
Heating
- Collisions share this kinetic energy with surrounding atoms, so the fuel and coolant become hot.
Final output
- Thermal energy ends up as electrical energy in the generator, with the rest wasted to the surroundings.
Efficiency
- Like other thermal power stations, much of the energy is lost as heat in cooling water and to the air.
Section 2 of 5Types of Waste
Types of Waste
Spent fuel
- Used fuel rods contain daughter nuclei and unused fuel, and they are highly radioactive and hot.
Intermediate level
- Items such as reactor parts and filters are contaminated and need shielding but cool without special systems.
Low level
- Gloves, clothing and tools contain small amounts of radioactive material and can be stored in sealed containers.
Gaseous and liquid
- Small discharges of gas and water are monitored carefully and kept below legal limits.
Section 3 of 5Managing Waste
1
Spent fuel is first stored under water in cooling ponds for several years, where water carries heat away and absorbs radiation.
2
It may then be reprocessed to remove unused uranium and plutonium for use as new fuel.
3
The remaining high-level waste can be mixed into glass blocks, which hold the radioactive material in a solid form.
4
The blocks are stored in sealed steel containers in shielded buildings, with some countries planning deep underground repositories.
5
Sites are monitored for decades, since some waste stays radioactive for thousands of years.
Section 4 of 5Why Waste Is a Problem
Long half-lives
- Some fission products and plutonium have half-lives of thousands of years, so they remain hazardous for very long periods.
Health risk
- Ionising radiation can cause cancer and other damage if radioactive material escapes into the environment.
Security
- Material must be guarded so that it cannot be stolen or misused.
Public concern
- Many people worry about where waste should be stored, which makes decisions on new sites difficult.
Section 5 of 5Exam Checklist & Tips
6.4.4 – Key Points for the Exam
- Spent fuel Fuel rods that have been used in a reactor and are no longer efficient for fission.
- Reprocessing Chemical treatment of spent fuel to recover uranium and plutonium.
- Cooling pond A water-filled storage pool for freshly removed spent fuel.
- High-level waste The most radioactive waste, which also generates a lot of heat.
- Decommissioning Safely dismantling a power station when it reaches the end of its life.
Common Mistakes
- Saying nuclear waste is only a problem because it is hot; it also gives out harmful ionising radiation.
- Believing that radioactive waste can be made safe by burning or chemical reactions;
- only time reduces its activity.
- Forgetting that spent fuel contains unused uranium that can be recovered.
- Mixing up energy stores, for example saying fission converts chemical energy into electricity.