Control Rod Action

Question:

How does boron-steel rods in the control rods regulate the nuclear reaction? Do the rods absorb the neutrons presence?

Answer:

You are correct. The boron nuclei in the control rods have a very high probability of absorbing a thermal (slow) neutron due to a good match between the energy delivered by the neutron that required to cause an alpha particle to be emitted by the boron nucleus.