Patent Number: 
Section: claims

1. 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, andsecuring 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. 2. The method of claim 1, wherein the reactor coolant pump further comprises a pump diffuser that is not a component of the unitary pump assembly formed by the pre-assembling, and the installing further comprises:disposing the pump diffuser inside the pressure vessel assembly in an operation other than the inserting and the securing operations. 3. The method of claim 2, wherein the installing includes disposing the pump diffuser inside the pressure vessel assembly before performing the inserting, and the inserting includes inserting the impeller and the driveshaft through the opening of the vessel head so as to position the impeller inside the pump diffuser. 4. The method of claim 2, wherein the opening of the vessel head through which the impeller and drive shaft are inserted is too small for the pump diffuser to pass through, and the disposing comprises:inserting the pump diffuser into the pressure vessel assembly through a manway of the vessel body that is separate from the opening of the vessel head through which the impeller and drive shaft are inserted. 5. The method of claim 2, wherein the disposing of the pump diffuser inside the pressure vessel assembly is performed before the inserting of the impeller and the driveshaft of the pump assembly through the opening of the vessel head. 6. The method of claim 2, further comprising:subsequent to installing the reactor coolant pump on the PWR, removing the pump assembly from the PWR while leaving the pump diffuser disposed inside the pressure vessel assembly. 7. The method of claim 1, wherein the inserting and securing mounts the pump assembly on the pressure vessel assembly with the drive shaft of the pump assembly oriented vertically and the pump motor disposed above the impeller. 8. The method of claim 1, wherein the vessel head includes a first mating flange and the vessel body includes a second mating flange, and the vessel head is secured to the vessel body by a step of securing the first mating flange to the second mating flange. 9. The method of claim 1, wherein the PWR further comprises a separator plate that separates the pressure vessel assembly into a pressurizer volume disposed above the separator plate and a reactor volume disposed below the separator plate, and at least a portion of the pump motor of the reactor coolant pump is disposed above the separator plate.