Theme E — Nuclear and Quantum Physics
E.4.5 Radioactive Waste Management — IB Physics HL Revision Notes & Topical Questions
5 min read 9 parts Lesson 36 of 45 1 quiz
Curriculum Equation Key Radioactive Decay & Half-Life FormulasFast Exam Solution
N(t) = N₀ × (1/2)t / t½ | λ = ln(2) / t½ ≈ 0.693 / t½ | E = Δm × c²
Lesson summary
E.4.5 Radioactive Waste Management — IB PHYSICS SL notes: Classify nuclear waste and evaluate storage and disposal methods using half-lives and hazards.Fission products — neutron-rich fragments such as caesium-137 and strontium-90.Activation products — materials such as steel, cl…
- Transuranic elements
- Reprocessing reduces volume and the longest-lived component
- Activity falls as A
- Activity per kilogram falls fastest at first
- Burial sites must be geologically stable, secure from attack and designed for safety
- Worker safety
Part 1 of 7Sources of waste
Fission products
- Fission products neutron-rich fragments such as caesium-137 and strontium-90.
Activation products
- Activation products materials such as steel, cladding and coolant impurities that absorb neutrons and become radioactive.
Transuranic elements
- Transuranic elements such as plutonium-239 formed when uranium-238 captures a neutron.
- Plutonium-239 has a half-life of about 24 000 years.
Other waste comes from mining, medicine, research and decommissioning.
Part 2 of 7Types of waste
| Type | Examples | Handling |
|---|---|---|
| Low-level | Lightly contaminated clothing, gloves, tools | Radioactive for a few years; encased in concrete and stored a few metres underground |
| Intermediate-level | Decommissioning waste, reactor parts, filters | Longer half-life; encased in cement in steel drums and stored securely underground |
| High-level | Spent fuel rods and fission products | Radioactive for thousands of years; very hot; handled and stored most carefully |
- High-level waste is about 3% of the volume but about 95% of the radioactivity.
Part 3 of 7Treatment of high-level waste
1
Spent fuel is cooled for several years in water ponds near the reactor.
2
Uranium and plutonium may be recovered by reprocessing to be used again.
3
Liquid waste is mixed with molten glass and solidified (vitrification).
4
The glass is sealed in steel, lead or concrete containers.
5
Containers are stored deep underground in stable rock behind several barriers.
Reprocessing reduces volume and the longest-lived component
- Reprocessing reduces volume and the longest-lived component but raises weapons proliferation concerns.
Dry storage in steel and concrete casks may be used before final disposal.
Part 4 of 7Why half-life matters
1
Danger depends on both activity and half-life.
- Short half-life (iodine-131, 8 days) — decays fast but is very active at first.
- Medium half-life (caesium-137 and strontium-90, about 30 years) — dominates the hazard for a few centuries.
- Long half-life (plutonium-239, millions of years for some products) — lower activity but needs isolation for thousands of years.
2Activity falls as A
A0(1/2)t/T½ — after ten half-lives it drops by a factor of about 1000.
3Activity per kilogram falls fastest at first
- Activity per kilogram falls fastest at first short-lived products dominate early activity.
Part 5 of 7Advantages and disadvantages of nuclear power
| Advantages | Disadvantages |
|---|---|
| No greenhouse gases in operation | Hazardous waste lasting thousands of years |
| High energy density | Potential for catastrophic accidents such as Chernobyl |
| Large reserves of fissionable material | Potential misuse in weapons or attacks |
| Reliable and now regarded as safe | Dangers in mining uranium |
Part 6 of 7Safety and environmental considerations
Isotopes with long half-lives must not enter water and food supplies.
Burial sites must be geologically stable, secure from attack and designed for safety
- and space for them is limited.
Worker safety
- Worker safety remote handling of fuel, thick shielding and emergency shutdown by lowering control rods.
Strategies
- Strategies minimise volume, segregate by activity and half-life, use barriers, monitor sites and keep records.
Transmutation research
- Transmutation research turning long-lived isotopes into shorter-lived ones by neutron bombardment.
Public concern
- Public concern radiation is invisible, so education helps society make informed decisions.
Part 7 of 7More from the specification
1Thermal decay power in spent fuel
- Thermal decay power in spent fuel freshly removed nuclear fuel rods emit significant radioactive decay power, requiring cooling pond immersion.
2Daughter nuclei
- The smaller nuclei produced in fission.
3Chain reaction
- Neutrons from one fission trigger further fissions.
4Unstable nucleus
- A nucleus with an imbalance of protons and neutrons that may decay.
5Reaction
- The partner force acting on the other object.
6Thermal
- A convection current in the air.
7Spontaneous
- A process which cannot be influenced by environmental factors such as temperature or pressure.
8Efficiency
- Useful output divided by total input.
9Moderator
- Material that slows neutrons.
10Specific energy
- Energy released per unit mass of a fuel, in J kg−1
11Binding energy
- The minimum energy required to separate the nucleons of a nucleus to infinity.
12Induced fission
- Fission caused by absorption of a neutron.
Key terms
| Term | Meaning |
|---|---|
| High-level waste | Highly radioactive, heat-generating waste such as spent fuel. |
| Vitrification | Incorporating waste into glass for storage. |
| Deep geological repository | Sealed underground storage in stable rock. |
| Reprocessing | Chemical separation of uranium and plutonium from spent fuel. |
| Transuranic | Element heavier than uranium, such as plutonium. |
| Activation product | Material made radioactive by neutron absorption. |
Avoid these mistakes
1
Believing waste with a long half-life is always more dangerous — its activity per atom is lower, though it lasts longer.
2
Thinking high-level waste has a large volume — it is a small share of volume but holds most of the radioactivity.
3
Confusing reprocessing with disposal — reprocessing recovers fuel but still leaves waste.
4
Forgetting that spent fuel is hot and generates heat.
5
Saying waste becomes harmless after one half-life — only half of the activity has gone.
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