A technician prepares a container for used fuel from a research reactor. Fig. 1 shows the transport cask with a steel shell, thick concrete and a water-fill...
Question 1 Report
A technician prepares a container for used fuel from a research reactor. Fig. 1 shows the transport cask with a steel shell, thick concrete and a water-filled inner space. The fuel continues to emit ionising radiation after it has been removed from the reactor. A warning meter beside the cask reads 6.0 mSv h-1 without its outer concrete lid and 0.15 mSv h-1 when the lid is fitted.
(a) Which type of radiation is most likely to need thick concrete shielding: alpha, beta or gamma? [2]
(b) Describe two ways in which the cask design reduces the risk to workers. [3]
(c) Calculate by what factor the dose rate is reduced when the lid is fitted. [2]
(d) Use the information in Fig. 1 to give one reason why water is kept around the used fuel. [3]
Answer Details
- Gamma radiation needs thick concrete shielding because it is the most penetrating of the three types listed and needs dense, thick material to reduce it effectively. [2]
- The thick concrete absorbs or reduces gamma radiation; the steel provides additional shielding and containment; the water absorbs radiation; and the sealed cask prevents radioactive material being released. Any three correctly linked design features are credited. [3]
- \[\text{reduction factor}=\frac{6.0\text{ mSv h}^{-1}}{0.15\text{ mSv h}^{-1}}=40\]The dose rate is reduced by a factor of 40. [2]
- Water around the fuel absorbs radiation, reducing the radiation dose outside the cask. It can also remove heat from fuel that remains radioactive. [3]
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