Nuclear fission and fusionAQA A-Level Physics: Mind map

Exam questions on Nuclear fission and fusion

1. Uranium-235 nuclei can be split by slow-moving neutrons. One fission reaction is ¹n + ²³⁵U → ¹⁴¹Ba + ⁹²Kr + 3 ¹n, and about 200 MeV of energy is released in each fission.
   Explain how a chain reaction can occur in a block of uranium-235.2 marks
2. A thermal nuclear reactor has fuel rods of uranium-235, a graphite moderator, boron control rods and a carbon dioxide coolant.
   Explain why a moderator is needed in a thermal reactor.2 marks
3. A thermal reactor operates in a steady state at a thermal power of 3.0 GW. Each fission of uranium-235 releases on average 200 MeV of energy and 2.4 neutrons. A uranium-235 atom has a mass of 235 u, where 1 u = 1.661 × 10⁻²⁷ kg; 1 MeV = 1.60 × 10⁻¹³ J.
   Explain how the control rods keep the reactor operating in a steady state.3 marks