IB Physics SL
Topic 5 — Fission
Paper 1 & 2
low, intermediate & high level
~8 min read
Managing Radioactive Waste
Nuclear power is clean at the point of use — no smoke, no carbon dioxide. But it leaves behind waste that can stay dangerous for thousands of years. How that waste is sorted, treated, and stored is one of the biggest challenges of the technology, and it’s exactly the kind of balanced judgement examiners love to test.
📘 What you need to know
- There are three types of nuclear waste: low-level, intermediate-level, and high-level
- The higher the level, the more radioactive, the longer the half-life, and the more careful the disposal
- Low-level (clothing, gloves, tools) is encased in concrete and stored a few metres underground
- Intermediate-level (from decommissioning) is set in cement in steel drums and stored securely underground
- High-level (spent fuel, fission products) is the most dangerous — hot and radioactive for thousands of years
- High-level waste is cooled in ponds, then made solid by vitrification (mixing with molten glass) and buried deep underground
- Nuclear power has real advantages (no greenhouse gases, high energy density) and disadvantages (hazardous waste, accident risk)
Three Levels of Waste
Not all nuclear waste is equally dangerous, so it’s sorted into three levels by how radioactive it is and how long it stays that way. The rule of thumb: as you go up the levels, the activity rises, the half-life lengthens, and the disposal gets more elaborate.
| Level | What it is | How dangerous | How it’s stored |
|---|
| Low-level | Lightly contaminated clothing, gloves, tools | Radioactive for a few years | Encased in concrete, stored a few metres underground until safe for regular disposal |
| Intermediate-level | Waste from decommissioning a power station | Longer half-life than low-level | Set in cement in steel drums, stored securely underground |
| High-level | Spent fuel rods and fission products | Most dangerous; hot and radioactive for thousands of years | Cooled in ponds, vitrified, encased, buried deep underground |
low-level
→ rising activity & half-life →
intermediate
→
high-level (most dangerous)
Why High-Level Waste Is the Problem
High-level waste is the real headache. As well as being intensely radioactive, spent fuel rods are extremely hot and must be handled far more carefully than the other types. There’s a further twist: inside the fuel rods, uranium-238 decays into plutonium-239, which is classed as high-level waste in its own right. Plutonium-239 is extremely radioactive and has a very long half-life of about 24 000 years, so it poses a long-term risk of contamination that lasts far beyond any human lifetime.
Treating High-Level Waste
Because high-level waste stays dangerous for so long, it goes through a careful sequence before disposal.
🧭 How high-level waste is dealt with
- Cool it — the waste is first placed in ponds of water near the reactor for several years
- Reclaim useful isotopes — plutonium and uranium are harvested to be used again
- Vitrify it — the waste is mixed with molten glass and made solid (this is called vitrification)
- Encase it — sealed in containers of steel, lead, or concrete
- Bury it deep — stored very deep underground in a geologically stable location
The lower waste levels are buried too, but less deeply — the depth and care scale with the danger. Vitrification matters because turning the waste into stable glass locks the radioactive material in place, so it can’t leak out into groundwater.
Environmental & Safety Considerations
Storing waste safely raises real practical problems. Isotopes with long half-lives must be kept out of water and food supplies. Burial sites have to be geologically stable, secure from attack, and designed for long-term safety — and suitable space for them is limited. For workers, fuel rods are handled remotely by machines, the reactor is wrapped in thick lead or concrete shielding, and in an emergency the control rods are fully lowered to stop all fission — an emergency shutdown.
Advantages & Disadvantages of Nuclear Power
Whether nuclear power is “worth it” is a genuine judgement with strong points on both sides. A good exam answer weighs them fairly.
✅ Advantages
- No greenhouse gases produced during operation — climate-change friendly
- High energy density — uranium yields far more energy per kg than fossil fuels
- Plentiful fuel — reserves of fissionable material outlast fossil fuel reserves
- Reliable and safe — now one of the safest, most reliable ways to generate electricity
⚠ Disadvantages
- Hazardous waste — dangerous and costly to manage, dangerous for thousands of years
- Accident risk — a meltdown (e.g. Chernobyl) could be catastrophic for the surroundings
- Risk of misuse — nuclear material and know-how could be diverted to weapons
- Mining harms — uranium mining carries risks to workers and the environment
Quick recap: waste is sorted into low, intermediate, and high levels by activity and half-life; high-level waste is cooled, vitrified, encased, and buried deep; and nuclear power trades no greenhouse gases and high energy density against long-lived hazardous waste and accident risk.
WE 1Explain why high-level waste is more difficult to manage than low-level waste, and describe two steps taken when disposing of it.
Why high-level is harder
it is far more radioactive and stays radioactive for thousands of years (long half-life)
spent fuel rods are also extremely hot, so must be handled very carefully
→ low-level waste is only radioactive for a few years, so needs far less care
Two disposal steps
it is mixed with molten glass and made solid (vitrification)
then encased and buried deep underground in a stable location
→ this locks the waste away from groundwater long-term
WE 2Give one advantage and one disadvantage of generating electricity from nuclear power rather than burning coal.
Advantage
nuclear power produces no greenhouse gases during operation
(coal releases large amounts of carbon dioxide)
→ nuclear is more climate-change friendly
Disadvantage
nuclear produces hazardous radioactive waste that stays dangerous for thousands of years
this is difficult and expensive to store safely
→ coal does not leave long-lived radioactive waste
💡 Top tips
- Match the level to the treatment: low-level → concrete, shallow; high-level → vitrified and buried deep
- Know the keyword “vitrification” — mixing waste with molten glass to make it a stable solid
- Plutonium-239 is the long-term worry — very long half-life (~24 000 years), classed as high-level
- For “evaluate” questions, give both sides: a clear advantage and a clear disadvantage, then a brief judgement
⚠ Common mistakes
- Treating all waste the same — the level sets how carefully it must be stored
- Saying high-level waste is only dangerous briefly — it stays radioactive for thousands of years
- Forgetting the plutonium-239 problem — formed from U-238 in the fuel, with a very long half-life
- Giving a one-sided answer to an evaluation question — examiners want both advantages and disadvantages
That completes the Fission topic — from a single split all the way to running a power station and cleaning up after it. You can now handle both the physics (energy, chain reactions, reactor components) and the evaluation questions on waste and safety, which are common in Paper 2.
Want this to actually click before the exam?
Book a free meeting and let’s work through the tricky bits together.
Book your free meeting