The reactor vessel, which houses the core, is the central component of the reactor coolant system (RCS).
The vessel has a cylindrical shell with a spherical bottom head and a ring flange at the top. A closure head is bolted to this flange.
Typically, the vessel is constructed of low alloy steel with an internal stainless steel cladding to protect the vessel from corrosion. The vessel with closure head is almost 41 ft. (12.5 m) tall and has an inside diameter of 171 in. (4343 mm). The minimum thicknesses of the shell wall and inside cladding are 8.4 and 0.125 in. (213 and 3.18 mm), respectively. Reflective metal (mirror)
insulation is installed on the exterior surfaces of the reactor vessel.