Fuel Rods: Contain the fissile material (e.g., Uranium-235). They are arranged in a grid to allow coolant and moderators to flow between them.
Moderator: A material like water or graphite that surrounds the fuel. Its purpose is to slow down fast-moving neutrons through collisions, increasing the probability of further fission.
Control Rods: Made of neutron-absorbing materials like boron or cadmium. They are inserted or withdrawn from the core to regulate the reaction rate by removing excess neutrons.
Coolant: A fluid (water, CO2, or liquid metal) that circulates through the core to absorb the heat generated by fission and transport it to a heat exchanger or turbine.
Shielding: Thick layers of concrete and steel (often 2+ meters) that surround the reactor to absorb hazardous gamma radiation and stray neutrons, protecting personnel and the environment.
Subcritical: If fewer than one neutron per fission causes a new fission, the reaction will eventually die out.
Critical: The reaction is self-sustaining at a constant rate. This is the normal operating state for power generation.
Supercritical: If more than one neutron per fission causes a new fission, the reaction rate increases exponentially. This state is used briefly during startup to increase power levels.
SCRAM: An emergency shutdown procedure where all control rods are fully inserted into the core instantly to stop the chain reaction.
| Component | Primary Material | Function | Effect on Reaction |
|---|---|---|---|
| Moderator | Water, Graphite | Slows down neutrons | Increases fission probability |
| Control Rods | Boron, Cadmium | Absorbs neutrons | Decreases reaction rate |
| Coolant | Water, CO2 | Transfers heat | Prevents core meltdown |
Energy Conversions: Always be ready to trace the energy path: Nuclear Potential Energy Kinetic Energy of fragments Thermal Energy of coolant Kinetic Energy of turbine Electrical Energy.
Safety Features: When asked about safety, mention both the shielding (containment) and the control rods (regulation).
Neutron Speed: Remember that 'fast' neutrons are the products of fission, but 'slow' (thermal) neutrons are the initiators of fission in U-235 reactors.
Waste Management: Fission products are often highly radioactive with long half-lives; exams frequently ask about the environmental and storage challenges associated with 'spent' fuel.
