Nuclear safety aspectsAQA A-Level Physics: Subtopic test

1. 1
   A nuclear power station uses fuel rods containing enriched uranium-235. The rods are replaced every 18 months. The spent fuel removed from the reactor is hot and highly radioactive.

   (a)

   Why is spent fuel moved using remotely controlled machines?

   [1 mark]

   • AContact with a person would start a chain reaction in the fuel.
   • BSpent fuel reacts explosively with air.
   • CThe fuel becomes radioactive only when people handle it.
   • DIt emits intense ionising radiation, so workers must be kept at a distance.

   (b)

   Which shielding is most suitable for absorbing the gamma radiation and neutrons from the reactor core?

   [1 mark]

   • AA sheet of paper
   • BA thin sheet of aluminium
   • CSeveral metres of concrete and a thick steel vessel
   • DA one metre gap of air

   (c)

   Explain why spent fuel rods are stored under water in cooling ponds for several years.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A thermal nuclear reactor is operating at a steady rate when sensors detect an earthquake and an emergency shutdown is started.

   (a)

   What action is taken immediately in an emergency shutdown?

   [1 mark]

   • AThe fuel rods are removed and placed in storage immediately.
   • BThe control rods are fully inserted into the core.
   • CThe flow of coolant is switched off.
   • DMore moderator is added to slow the neutrons further.

   (b)

   The core still needs cooling for some time after the shutdown. Why?

   [1 mark]

   • ARadioactive decay of the fission products continues to release thermal energy.
   • BFission continues at the same rate until the rods have cooled.
   • CThe moderator keeps causing fission after the control rods are inserted.
   • DThe coolant has become fissile.

   (c)

   Explain how inserting the control rods stops the chain reaction.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A nuclear power station produces three types of waste: low-level waste (such as contaminated clothing and tools), intermediate-level waste (such as reactor components and fuel cladding) and high-level waste (spent fuel containing fission products). Caesium-137, a fission product, has a half-life of 30 years. The high-level waste also contains plutonium-239, which has a half-life of 24 000 years.

   (a)

   Explain why high-level waste must be stored for much longer and more securely than low-level waste.

   [3 marks]

   (b)

   Calculate the time taken for the activity of a sample of caesium-137 to fall to 0.10% of its initial value.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A country plans to build a new nuclear power station on its coast. The plan includes burying its high-level waste in a deep underground repository. Burning 1.0 kg of coal releases about 3.0 × 10⁷ J of energy, whereas the complete fission of 1.0 kg of uranium-235 releases about 8 × 10¹³ J.

   (a)

   Describe and explain the measures that protect workers and the public from radiation when the power station is operating and when fuel and waste are handled.

   [6 marks]

   (b)

   Evaluate the balance of risks and benefits of nuclear power compared with burning coal.

   [6 marks]

   Total for question 4: 12 marks

End of questions