Control Rods: These are made from materials like boron that absorb neutrons without becoming unstable. They are lowered into the core to decrease the rate of fission or raised to increase it, ensuring exactly one neutron from each fission causes another reaction.
Moderator: This material, typically water or graphite, surrounds the fuel rods to slow down high-speed neutrons. Slower neutrons, known as thermal neutrons, are much more efficiently absorbed by the Uranium fuel, allowing the reactor to maintain a steady chain reaction.
Shielding: To protect workers and the surrounding environment, reactors are encased in a steel and concrete wall that can be nearly 2 metres thick. This barrier is designed to absorb harmful radiation, including gamma rays and neutrons produced by radioactive decay products.
Nuclear fusion is the process where two light atomic nuclei join to produce a larger nucleus. This reaction occurs naturally in stars, where hydrogen isotopes like deuterium and tritium fuse to form helium, releasing a massive amount of energy derived from mass conversion.
On Earth, fusion is extremely difficult to achieve because atomic nuclei are positively charged and repel each other via electrostatic repulsion. To overcome this force, the nuclei must be moving at extremely high speeds, which requires temperatures of millions of degrees and very high pressures.
While both processes release immense energy, they operate on opposite ends of the periodic table and have distinct environmental profiles. Fission utilizes heavy elements and produces long-lived radioactive waste, whereas fusion uses light elements and produces stable helium.
| Feature | Nuclear Fission | Nuclear Fusion |
|---|---|---|
| Process | Nuclei splitting apart | Nuclei joining together |
| Nuclei Size | Large (e.g., Uranium) | Small (e.g., Hydrogen) |
| Environment | Nuclear reactors on Earth | Stars and experimental reactors |
| Requirements | Thermal neutrons to induce | Extreme temperature and pressure |
Neutron Management: When writing about reactors, clearly distinguish between the moderator (changes neutron speed) and control rods (changes neutron quantity). Examiners often look for these specific keywords and their respective functions in multiple-choice and long-form answers.
Balancing Equations: Ensure the total mass number and atomic number are identical on both sides of a nuclear equation. For example, in fission equations, check that the sum of the daughter nuclei and the neutrons equals the initial fuel nucleus plus the absorbed neutron.
Energy Logic: Remember that energy is released because the product nuclei are more stable than the reactants. This stability comes from a small loss of mass, which is converted into kinetic energy and gamma radiation during the reaction.
