Nuclear Power: Uranium Fission, Reactors and Thermonuclear Fusion
Splitting heavy nuclei and fusing light ones both release enormous energy from a tiny loss of mass
Big idea: The nucleons in a nucleus are bound together, and re-arranging them toward the most tightly bound nuclei (near iron on the binding-energy curve) releases energy. A heavy 235U nucleus can be split (fission), and two light nuclei such as deuterium and tritium can be fused. In both cases a small mass defect Δm reappears as energy through E = Δm c2. A single uranium fission releases about 200 MeV — roughly ten million times the energy of burning one carbon atom.
By the end of this topic you will be able to:
- explain why both fission of heavy nuclei and fusion of light nuclei release energy, using the binding-energy-per-nucleon curve;
- write and read the fission reaction of 235U and describe the role of the emitted neutrons;
- define a chain reaction, critical mass and the multiplication factor k;
- describe the parts of a nuclear reactor — fuel, moderator, control rods, coolant — and what each does;
- state the conditions needed for controlled thermonuclear fusion and describe a tokamak;
- compute the energy released in fission and fusion reactions from the mass defect.