Fig. 1 shows the layered shielding around a compact research reactor at a university. Fuel rods undergo fission in the central core. A graphite moderator sl...
Question 1 Report
Fig. 1 shows the layered shielding around a compact research reactor at a university. Fuel rods undergo fission in the central core. A graphite moderator slows neutrons, and control rods absorb some neutrons. Water carries thermal energy away from the core. Thick concrete surrounds the vessel. The reactor does not produce electrical current directly in this diagram, but heat can later be used to make steam and drive a generator. During maintenance, staff use remote tools and radiation monitors because several types of radiation may be present near the reactor.
(a) Name the radiation that is most difficult to stop with shielding. [1]
(b) Describe the purpose of the graphite moderator and the control rods. [2]
(c) Explain three ways in which the shielding and remote handling reduce risks to workers. [3]
Answer Details
(a) Gamma radiation is the most difficult of the common nuclear radiations to stop with shielding because it is highly penetrating. [1]
(b) The graphite moderator slows neutrons. The control rods absorb neutrons, controlling the number available to cause further fission and therefore controlling the chain reaction. [2]
(c) Three valid risk reductions are:
- Thick concrete absorbs radiation, reducing the radiation that reaches workers.
- Water provides shielding and also removes thermal energy from the core.
- Remote tools increase the distance between workers and the source, reducing exposure.
- Remote handling also reduces the time spent close to the source.
- Radiation monitors warn staff if radiation levels become high.
Any three of these explained points gain credit. [3]
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