1. 1
   A nuclear power station uses uranium-235 fuel rods inside a reactor core. When a slow-moving neutron is absorbed by a U-235 nucleus, the nucleus splits apart into two smaller daughter nuclei, releasing two or three fast neutrons and a large amount of energy. Engineers surround the fuel rods with a graphite moderator and insert boron control rods between the fuel rods to keep the reaction steady rather than letting it accelerate uncontrollably.

   (a)

   Which process describes what happens inside the fuel rods when a U-235 nucleus absorbs a neutron?

   [1 mark]

   • ANuclear fission
   • BNuclear fusion
   • CRadioactive alpha decay
   • DElectromagnetic induction

   (b)

   What is the purpose of the boron control rods described in the scenario?

   [1 mark]

   • ATo speed the neutrons up so that more fission occurs
   • BTo absorb some of the neutrons produced, so the rate of fission stays steady
   • CTo convert the kinetic energy of the neutrons directly into electricity
   • DTo fuse hydrogen nuclei together inside the reactor core

   (c)

   Explain what must happen to the neutrons released during each fission event for a controlled chain reaction to continue, and explain why the graphite moderator is needed for this to happen effectively.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Inside the core of the Sun, hydrogen nuclei collide with each other at extremely high temperatures and pressures. When two small nuclei join together, a larger nucleus is formed and energy is released because the resulting nucleus has slightly less mass than the two nuclei that combined. This process, rather than the burning of a fuel, is what has kept the Sun radiating energy for billions of years.

   (a)

   What name is given to the nuclear process described in the scenario, in which two small nuclei join to form a larger nucleus?

   [1 mark]

   • ABeta decay
   • BNuclear fission
   • CNuclear fusion
   • DGamma emission

   (b)

   Which quantity decreases overall as a result of the process described in the scenario?

   [1 mark]

   • AThe size of the resulting nucleus compared with each starting nucleus
   • BThe total electric charge of the particles involved
   • CThe total number of protons involved
   • DThe total mass of the particles involved

   (c)

   Explain why the process described in the scenario cannot take place at the low temperatures and pressures found in a laboratory on Earth.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A physics student is asked to compare two nuclear reactions being researched for generating electricity. In the first, a large uranium-235 nucleus is struck by a neutron and splits apart. In the second, which scientists are trying to reproduce on Earth inside experimental reactors, two small hydrogen nuclei are forced together to form a larger helium nucleus.

   (a)

   Describe what happens during the first reaction referred to in the scenario, including what is produced and released.

   [3 marks]

   (b)

   Explain two differences between the first and second reactions referred to in the scenario, and state why the second reaction is much harder to maintain as a practical, economic power station on Earth.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A government is deciding whether to replace an ageing coal-fired power station with a new nuclear fission power station. The proposal includes building the reactor close to a coastal town, with spent fuel stored on site for several decades before being moved to a long-term underground storage facility.

   (a)

   Evaluate the advantages and disadvantages of building the nuclear fission power station described, compared with continuing to use the coal-fired power station.

   [6 marks]

   (b)

   The government is also advised that nuclear fusion could one day replace nuclear fission as a cleaner way of generating electricity. Explain why fusion power stations are not yet a practical alternative to the fission power station described in the scenario.

   [6 marks]

   Total for question 4: 12 marks

End of questions