Thick-walled cylindrical steel vessel enclosing the reactor core in a nuclear power plant. The vessel is made of a special fine-grained steel well suited for welding and with a high toughness while showing low porosity under neutron irradiation. The inside is lined with austenitic cladding to protect against corrosion. For a 1,300 MWe pressurized water reactor, the pressure vessel is about 12 m high, the inner diameter is 5 m, and the wall of the cylindrical shell is about 250 mm thick. The overall weight amounts to approx. 530 t without internals. The vessel is designed for a pressure of 17.5 MPa (175 bar) and a temperature of 350 ยฐC.