Pressurized water reactor with upper vessel section providing both pressure and flow control

A method comprising:

• installing a reactor coolant pump comprising a pump motor, a driveshaft, an impeller, and a mounting flange on a pressurized water reactor (PWR) comprising a pressure vessel assembly comprising a vessel body and a vessel head defining an integrated pressurizer volume secured thereto, and a nuclear reactor core disposed in the pressure vessel assembly, the installing including:
• pre-assembling the pump motor, the driveshaft, the impeller, and the mounting flange outside of the pressure vessel assembly to form a pump assembly as a unit disposed outside of the pressure vessel assembly in which the pump motor is connected with the impeller by the driveshaft,
• inserting the impeller and the driveshaft of the pump assembly through an opening of the vessel head while the pump motor remains outside of the pressure vessel assembly, and
• securing the flange of the pump assembly to an outside of the vessel head to mount the pump assembly on the pressure vessel assembly,
• wherein the inserting and securing mounts the pump assembly on the pressure vessel assembly with the drive shaft of the pump assembly oriented vertically so that no portion of the pump assembly is disposed in the pressurizer volume.