Patent Number: 
Section: claims

1. An apparatus comprising:a pressurized water reactor (PWR) including a cylindrical pressure vessel with its cylinder axis oriented vertically, a cylindrical central riser disposed within the pressure vessel, so that a downcomer annulus is formed therebetween, a nuclear reactor core disposed in the cylindrical pressure vessel, and a separator plate disposed in the cylindrical pressure vessel that separates the pressure vessel to define an integral pressurizer volume disposed above the separator plate and a reactor vessel portion containing the nuclear reactor core disposed below the separator plate; anda reactor coolant pump including:a pump assembly including a pump motor, an impeller, and a vertical driveshaft that operatively connects the pump motor and the impeller as a pump assembly, anda pump diffuser configured to receive the impeller, the pump diffuser not being secured with the pump assembly,wherein the reactor coolant pump is mounted on the cylindrical pressure vessel of the PWR with the impeller disposed in the pump diffuser above the nuclear reactor core and adjacent both the separator plate and the top end of the central riser so that the impeller is disposed at a turnaround point of a primary coolant flow, with at least a portion of the pump motor being disposed above the separator plate and with no portion of the reactor coolant pump passing through the integral pressurizer volume,wherein at the turnaround point of the primary coolant flow reverses direction from an upward flow through the central riser to a downward flow through the downcomer annulus. 2. The apparatus of claim 1, wherein the pump motor is disposed above the impeller. 3. The apparatus of claim 1, wherein the reactor coolant pump is mounted on the cylindrical pressure vessel of the PWR with the impeller and pump diffuser disposed in the reactor vessel portion below the separator plate. 4. The apparatus of claim 1, wherein the pump diffuser is mounted on and supported by a support plate disposed below the separator plate, and wherein the impeller is not supported by the pump diffuser and is not supported by the support plate. 5. The apparatus of claim 4, wherein the support plate separates the suction and discharge sides of the pump diffuser. 6. The apparatus of claim 1, wherein the reactor coolant pump is mounted on the cylindrical pressure vessel of the PWR with the drive shaft passing through a vessel penetration of the cylindrical pressure vessel that is large enough for the impeller to pass through. 7. The apparatus of claim 6, wherein the vessel penetration of the cylindrical pressure vessel on which the reactor coolant pump is mounted with the drive shaft passing through is too small for the pump diffuser to pass through.