Nuclear Power

Nuclear power relies on the fission of Uranium nuclei and a controlled chain reaction where more nuclei are split.

Uranium

• Most Uranium atoms have 146 neutrons and 92 protons
• About 1/140 Uranium atoms lack 3 neutrons (143 neutrons and 92 protons)
• This type of Uranium atom has a total of 235 neutrons and protons → thus named U-235
• U-235’s nucleus is easily split by a strike of energy, leaving fission products, 2-3 neutrons, gamma rays, and a few neutrinos

Problem: Neutrons emitted from fission has too much kinetic energy to be captured by Uranium nuclei, leading to failure of chain reaction

• The fission rate is a too low → chain reaction fizzles out
• Solution 1: use a moderator to slow down neutrons
  • Graphite walls, water cells, etc
• Solution 2: put more U-235s increasing density and thus hit rate
  • Abundance is enriched to 4-7x its natural amount
  • To enrich: pass a gaseous Uranium compound through centrifuges separating lighter U-235s from heavier U-238s
  • This process is carefully regulated to control supply for bomb-grade fuel
• A combination of water (solution 1) and enrichment (solution 2) is used

Energy Generation

• As fission occurs energy is released as kinetic energy
• This kinetic energy is captured as heat by water in the reactor
• As the water heats up, steam drives a turbine that generates energy

Nuclear Meltdown & Waste

• Water flow to the reactor stops (due to leak for example) → fission product kinetic energy turn existing water in the reactor into steam → reactor dries up → Uranium melts creating radioactive gas → the gas escapes to the facility → if not contained, gas escapes to the atmosphere
• Nuclear wastes include spent fuel from the reactors, Uranium that never fissions, fission products, and plutonium → they must be isolated from the environment until they have decayed → most nuclear powerplants sit on their nuclear waste

Mechanics of Nuclear Powerplant

• Reactor
  • Uranium Oxide is compressed into fuel pellets and packed into sealed fuel rods
  • Fuel rods are bunched together to form fuel elements
  • Fuel elements are put in the water in the reactor vessel with 20cm thick steel seals
  • Bombarding the Uranium with neutrons leads to the chain reaction
    • After each fission, only 1 released neutron should cause a new fission
  • To control the chain reaction: boric acid in the water and lowered control rods absorb the oversupply of neutrons
• Primary Water Circuit
  • Energy from fission heats up water to 320 degrees celsius
  • The pressure regulator keeps everything under high pressure so the water does not boil or steam
  • The hot water passes through the circuit to a steam generator
• Secondary Water Circuit
  • The heat from hot water from the primary circuit boils the water in the steam generator → steam is created
  • The steam generated drives steam turbines
  • The steam turbine spins and drives a generator, producing electricity
  • Transformers increase the voltage of the electricity allowing transfer into the grid
  • The steam cools down in a condenser and returns to the steam generator
• Tertiary Water Circuit
  • Cooled water passes through a pipe that runs through the condenser
  • Warmed cooling water is brought to the cooling tower
  • At the cooling tower, the cooling water cools through contact with the ascending airflow
  • The majority of the cooling water is collected in a basin at the base of the cooling tower and returned to the condenser

Small Modular Reactors

• Can be manufactured in factories instead of built on construction sites
• Smaller, safer, cheaper (dollars per megawatt) → allows more locations and people to access nuclear power
• Learn more here