Question

In a nuclear reactor

• A. the chain reaction is kept under control by rods of cadmium, which reduces the rate
• B. the thick concrete shield is used to slow down the speed of fast neutrons
• C. heavy water (or graphite) moderate the activity of the reactor
• D. out of $U^{238}$ and $U^{235}$ natural uranium has less that 1% of $U^{235}$

Answer 1

Answer: (A), (C), (D)

The correct options are
A the chain reaction is kept under control by rods of cadmium, which reduces the rate
C out of $U^{238}$ and $U^{235}$ natural uranium has less that 1% of $U^{235}$
D heavy water (or graphite) moderate the activity of the reactor

Heavy water or Graphite are used as coolants and thick concrete shields are used to prevent radiation.