In a nuclear reactor, the moderator is used to
- A. absorb excess neutrons and shut the reactor down
- B. slow fast neutrons so that they are more likely to cause further fission
- C. cool the reactor core
- D. shield the operators from radiation
Explanation
Graphite or heavy water slows the neutrons through repeated collisions, because slow neutrons are far more readily captured by uranium 235 and sustain the chain reaction. Absorbing surplus neutrons to control the rate is the job of the control rods, usually boron or cadmium. Confusing the moderator with the control rods is the standard error here.