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7.3.2Nuclear Physics

Fuels in Nuclear Reactors

5 min read 5 parts Lesson 15 of 19 Unit quiz

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Section 1 of 5Reactor Fuels

7.3.2 Fuels in Nuclear Reactors
Uranium-235
  • The isotope used as fuel in most reactors; it undergoes fission when it absorbs a slow-moving neutron.
Plutonium-239
  • A second fissile isotope that undergoes fission and is used as a fuel in reactors.
Fuel rods
  • Rods containing the fuel are arranged in the reactor core, where fission releases energy as heat.
Coolant
  • Water flowing around the fuel rods carries the heat away from the core to the heat exchanger.

Section 2 of 5From Fission to Electricity

1
Fission in the fuel rods releases energy, which heats the water coolant surrounding the rods.
2
The hot coolant is pumped to a heat exchanger, where it transfers its energy to a separate supply of water.
3
The water in the separate supply boils to steam, and the steam turns a turbine connected to a generator.
4
The cooled coolant is then returned to the reactor core to be heated again.

Section 3 of 5Main Reactor Components

Main Reactor Components
Core
  • The region of the reactor containing the fuel rods, where fission takes place.
Heat exchanger
  • Transfers thermal energy from the hot coolant to the water that becomes steam.
Turbine
  • Driven by the steam so that it rotates a generator, which produces electricity.
Control rods
  • Absorb neutrons to control the rate of fission, as explained in the next lesson.

Section 4 of 5Worked Example

Question Complete the fission equation: ²³⁵₉₂U + ¹₀n → ¹⁴¹₅₆Ba + ⁹²₃₆Kr + ? ¹₀n.

  1. Mass numbers
    • 235 + 1 = 236;
      • 141 + 92 = 233, so 236 − 233 = 3 neutrons are needed on the right.
  2. Atomic numbers
    • 92 + 0 = 92;
      • 56 + 36 = 92, so they balance.

Answer 3 neutrons (³ ¹₀n)

Section 5 of 5Exam Checklist & Tips

7.3.2 – Key Points for the Exam

  • Fuel rod A rod containing fissile fuel placed in the reactor core.
  • Fissile Describes an isotope that can undergo fission when it absorbs a neutron.
  • Coolant The fluid that carries heat away from the reactor core.
  • Heat exchanger A device that transfers thermal energy from one water supply to another without mixing them.
  • Turbine A machine turned by steam to drive a generator.

Common Mistakes

  • Saying that a reactor burns uranium; the energy comes from fission, not from combustion.
  • Thinking the coolant water in the core turns into the steam that drives the turbine;
    • the steam is made in the separate water supply.
  • Stating that most reactors use plutonium-239 as fuel; uranium-235 is the most commonly used fuel.
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