Theme E — Nuclear and Quantum Physics
E.4.4 Operation of a Nuclear Reactor — IB Physics HL Revision Notes & Topical Questions
5 min read 9 parts Lesson 35 of 45 1 quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
E.4.4 Operation of a Nuclear Reactor — IB PHYSICS SL notes: Describe the roles of fuel, moderator, control rods, coolant, heat exchanger and shielding in a thermal fission reactor.A nuclear power station is a heat source — fission heats the coolant in the reactor core.The coolant…
- The coolant gives its heat to water in a heat exchanger
- Steam drives a turbine
- Fuel is uranium dioxide pellets enriched to 3–5% uranium-235
- The cladding holds in the radioactive fission products
- Part of the fuel is replaced every few years
- It surrounds the fuel and control rods
Part 1 of 7Overview of a power station
1A nuclear power station is a heat source
- A nuclear power station is a heat source fission heats the coolant in the reactor core.
2The coolant gives its heat to water in a heat exchanger
- The coolant gives its heat to water in a heat exchanger producing steam.
3Steam drives a turbine
- Steam drives a turbine and the turbine drives a generator.
4
Two factors must be controlled when the reactor produces power at the required rate.
- The number of free neutrons.
- The energy of the free neutrons.
Part 2 of 7Fuel rods
1Fuel is uranium dioxide pellets enriched to 3–5% uranium-235
- Fuel is uranium dioxide pellets enriched to 3–5% uranium-235 packed in zirconium alloy tubes.
2The cladding holds in the radioactive fission products
- The cladding holds in the radioactive fission products and withstands high temperature and radiation.
3
A core holds about 100 tonnes of fuel in tens of thousands of rods.
4Part of the fuel is replaced every few years
- Part of the fuel is replaced every few years because fission products build up and uranium-235 falls, reducing k.
Part 3 of 7Moderator
1Purpose
- Purpose to slow fast neutrons to thermal energies (about 0.025 eV).
2It surrounds the fuel and control rods
- It surrounds the fuel and control rods neutrons lose momentum in collisions with its nuclei.
3
A good moderator has light nuclei, absorbs few neutrons and is a liquid or solid.
- Water is cheap but absorbs some neutrons, so enriched fuel is needed.
- Heavy water absorbs very little, so natural uranium can be used; graphite is also used.
4
Thermal neutrons react efficiently with uranium-235 fuel.
Part 4 of 7Control rods
1Purpose
- Purpose to absorb neutrons; they are made of boron or cadmium.
2Lowering the rods absorbs more neutrons
- Lowering the rods absorbs more neutrons k falls below 1 and the fission rate decreases.
3Raising the rods absorbs fewer neutrons
- Raising the rods absorbs fewer neutrons and the fission rate increases.
4
Adjusted automatically so that exactly one neutron from each fission causes another
- k = 1.
5In an emergency all rods drop fully into the core
- In an emergency all rods drop fully into the core absorbing all free neutrons and shutting the reactor down.
6Moderator makes fission more likely by slowing neutrons
- Moderator makes fission more likely by slowing neutrons control rods make it less likely by removing neutrons.
Part 5 of 7Coolant and heat exchanger
1
The coolant (water, heavy water, carbon dioxide or liquid sodium) is pumped cold into the core — it carries heat from the fuel.
- In many reactors pressurised water is moderator and coolant; pressure stops it boiling.
2
The heat exchanger passes thermal energy from the primary coolant to a separate water system — producing steam.
- Radioactive material stays in the sealed primary loop.
3
Steam drives turbines, then a condenser cools it and returns the water.
4Efficiency is about one third
- Efficiency is about one third the rest is rejected as waste heat to a river, sea or cooling tower.
Part 6 of 7Shielding and safety
1
The reactor sits in a steel pressure vessel and a steel and concrete wall nearly 2 m thick or more — absorbing neutrons and gamma rays.
2
A containment building is the final barrier in an accident.
3Fission products keep decaying after shutdown
- Fission products keep decaying after shutdown this decay heat means cooling must continue for a long time.
4Fuel rods are handled remotely by machines
- Fuel rods are handled remotely by machines and workers' exposure is limited by shielding.
5Energy flow
- Energy flow nuclear store, kinetic energy of fragments, thermal energy of coolant and steam, kinetic energy of turbine, then electrical energy.
Part 7 of 7More from the specification
Chain reaction
- Neutrons from one fission trigger further fissions.
High-level waste
- Highly radioactive, heat-generating waste such as spent fuel.
Unstable nucleus
- A nucleus with an imbalance of protons and neutrons that may decay.
Reaction
- The partner force acting on the other object.
Spontaneous
- A process which cannot be influenced by environmental factors such as temperature or pressure.
Density
- Mass per unit volume.
Specific energy
- Energy released per unit mass of a fuel, in J kg−1
Binding energy
- The minimum energy required to separate the nucleons of a nucleus to infinity.
Induced fission
- Fission caused by absorption of a neutron.
Daughter nuclei
- The smaller nuclei produced in fission.
Energy density
- The energy available per unit mass or area of a resource.
Key terms
| Term | Meaning |
|---|---|
| Moderator | Material that slows fast neutrons to thermal energies. |
| Control rods | Neutron-absorbing rods used to regulate the chain reaction. |
| Coolant | Fluid that removes heat from the core. |
| Heat exchanger | Device transferring heat from primary coolant to water making steam. |
| Enrichment | Raising the proportion of uranium-235 in fuel. |
| Decay heat | Heat from decay of fission products after shutdown. |
| Shielding | Thick steel and concrete absorbing radiation from the core. |
Avoid these mistakes
1
Saying control rods slow neutrons — they absorb them.
2
Thinking the moderator and coolant are always the same substance — they may differ.
3
Believing a reactor can explode like a bomb — the fuel is too weakly enriched.
4
Forgetting that fission products keep generating heat after shutdown.
5
Giving 100% efficiency — real plants convert about a third of the heat to electricity.
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