What do you think is the purpose of the thick, concrete chamber surrounding the reactor of a nuclear power plant?

The purpose of the thick, concrete chamber surrounding the reactor of a nuclear power plant is to absorb the dangerous nuclear radiation so that the outside world can be protected.

Explanation

The concrete chamber surrounding the reactor of a nuclear power plant is commonly known as the "containment vessel". It is a thick concrete shield that absorbs neutrons and ionising radiation, which can be 5.5m thick in general practice.