What is the reactor vessel?

It is the main component of a nuclear power plant and contains the reactor core with its pressurised coolant/moderator, as well as the neutron reflector, thermal shielding, control rods and other internal structures.

In most reactor designs it consists of a vertical cylinder of low alloy carbon steel, weighing approximately 400 tonnes, 13 metres high, 5.50 metres in diameter and 20 to 30 centimetres thick, lined inside with a minimum thickness of 3 mm stainless steel and hermetically sealed by a steel lid of the same characteristics, which can be removed for refuelling.

It is considered a containment barrier to prevent radiation from fission reactions from being emitted to the outside.