Table 1 shows readings taken during training at a nuclear power station. An operator inserted the neutron-absorbing rods by different distances and recorded...
Question 1 Report
Table 1 shows readings taken during training at a nuclear power station. An operator inserted the neutron-absorbing rods by different distances and recorded the neutron detector count and electrical power output.
| Control-rod insertion / cm | Neutron count / s-1 | Electrical power / MW |
|---|---|---|
| 10 | 860 | 920 |
| 30 | 640 | 690 |
| 50 | 420 | 460 |
| 70 | 210 | 230 |
(a) State the relationship between control-rod insertion and neutron count shown in Table 1. [2]
(b) Calculate the percentage decrease in electrical power when the rods are moved from 10 cm to 70 cm insertion. [3]
(c) Explain why a smaller neutron count reduces the energy released each second by nuclear fission. [2]
(d) Describe three precautions the operator should use to reduce exposure to nuclear radiation while checking a detector near the reactor. [3]
Answer Details
(a) As control-rod insertion increases, the neutron count decreases. For example, it falls from \(860\text{ s}^{-1}\) at 10 cm to \(210\text{ s}^{-1}\) at 70 cm. [2]
(b)
\[\text{decrease}=920-230=690\text{ MW}\]
\[\text{percentage decrease}=\frac{690}{920}\times100=75\%\]
The electrical power decreases by 75%. [3]
(c) A lower neutron count means fewer neutrons are available to strike uranium nuclei. Therefore fewer fissions occur each second, so less energy is released each second. [2]
(d) Any three valid radiation-protection precautions are: minimise time near the source; maximise distance from it; use shielding such as lead or concrete; use remote handling equipment; and wear a radiation monitor or dosimeter. These reduce dose by reducing exposure time, increasing distance, blocking radiation, or monitoring accumulated dose. [3]
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