Reactor Cooling Pump (RCP)


This is a 3D model of a Reactor Cooling Pump (RCP).

3D Model Annotations

Mixed Flow Centrifugal Pump

This 3D model represents a mixed flow, single stage, single suction, centrifugal pump. This type of pump is used in reactor cooling water systems for circulating primary reactor coolant.

Discharge Nozzle

Primary coolant is discharged from the pump through this nozzle.

Suction Nozzle

Primary coolant is drawn into the pump through this nozzle.


This impeller is a mixed flow centrifugal impeller. The term ‘mixed flow’ refers to the axial flow into the base of the impeller and radial flow outwards from the impeller. This type of impeller is used for medium to high flow rates, and medium to high pressures; the design is similar to that of a Francis turbine.


The shaft transfers the rotary motion created by the electric motor to the impeller; it is held in alignment using bearings. Due to the shaft’s length, it is split into several parts, the pump half coupling, motor half coupling, and spacer coupling; these parts together are colloquially referred to as ‘the pump shaft’, although this is technically incorrect as the shaft is made-up of more than a single piece.

Guide Bearing

Radial loads exerted by the pump during operation are transferred to guide bearings. Self-aligning hydrostatic bearings are used to keep the shaft vertically aligned. Discharge pressure from the centrifugal pump impeller acts upon a bearing journal balance plate, which ensures the bearing -and shaft- alignment is correct whenever the pump is in operation.

Sealing Assembly

The sealing assembly of the pump is usually the area of the pump requiring the most maintenance interventions. 

Shaft sealing is accomplished in the upper part of the pump housing using a removable seal cartridge which contains three mechanical seals in series. Mechanical seals springs press the titanium carbide and stationary graphite faces together and ensure the faces remain aligned. The torturous flow path from the lower seal to the upper seal ensures little leakage through the shaft sealing assembly. To ensure parts of the mechanical seal do not fail due to high temperatures seal cooling is provided. Underneath the sealing assembly, an auxiliary impeller is keyed to the main impeller. Seal water flow through the seal cooler is provided by the auxiliary impeller. The mechanical seals are highlighted in light blue, and are numbered 1, 2 and 3, from top to bottom.


After liquid is discharged from the impeller, it flows through a diffuser. The shape of the diffuser causes the liquid’s velocity to decrease and its pressure to increase (Bernoulli’s principle); a volute casing performs the same function.

Electric Motor Rotor

An electric motor is used to rotate the impeller. RCP motors are alternating current squirrel cage induction type motors with a typical operating voltage of 13.8 kV (depending upon the design). This part of the motor is the rotor.

Electric Motor Stator

An electric motor is used to rotate the impeller. RCP motors are alternating current squirrel cage induction type motors with a typical operating voltage of 13.8 kV (depending upon the design). This part of the motor is the stator.

Space Coupling

The space coupling is installed between the pump half coupling and the motor half coupling; it can be removed to give personnel easier access to the shaft seal and thermal barrier.

Component Cooling Water (CCW)

The component cooling water (CCW) circuit is fed to an integral heat exchanger and the pump thermal barrier. CCW removes heat from the pump internals to prevent overheating. Both the integral heat exchanger (cooled primary loop water / CCW), and the CCW cooler (CCW / external cooling water circuit), use shell and tube heat exchangers.

Metallic O-Rings

O-rings and mechanical seals are installed at various places within the pump to seal/close unintended flow paths. At this highlighted location, two O-rings are installed between the pump casing and casing cover. If the inner O-ring fails, hot cooling water will flow via a drain path to a containment sump. Temperature sensors installed in the drain path alert personnel of any coolant flow.


A flywheel is a heavy, disc shaped, piece of metal, that smooths vibration. It does this by storing rotational energy and then using this energy to resist changes to the machine's rotational speed. The amount of energy stored in the flywheel is the square root of its rotational speed.

External Heat Exchanger

An external shell and tube heat exchanger transfers heat from the component cooling water (CCW) circuit to a heat sink e.g. cooling tower.

Motor Half Coupling

The bottom of the motor half coupling connects to the space coupling. Rotational motion from the motor half coupling is transferred to the space coupling.

Pump Half Coupling

The top of the pump half coupling connects to the spacer coupling. Rotational motion from the spacer coupling is transferred to the pump half coupling.

Upper Radial Bearing and Thrust Bearing

The upper radial bearing and thrust bearing are located within this area. Radial bearings handle radial loads (loads acting perpendicular to the pump shaft), whilst thrust bearings handle axial loads (loads acting parallel to the pump shaft).

Air Cooler

Air is cooled in an air cooler prior to being delivered to the space between the pump cover and motor housing; cooling air removes waste heat.

Air Duct

Cooling air is transferred via air ducts.

Lower Radial Bearing

The lower radial bearing caters for loads perpendicular to the motor shaft.

Auxiliary Impeller

The auxiliary impeller serves two main purposes. It provides pressure to the self-aligning journal bearing and provides a small amount of flow to the pump seals; flow to the pump seals is drawn through the thermal barrier.


To provide a means to determine seal leakage, a seal collection system is utilised. Leakage past the third mechanical seal is collected in a standpipe that surrounds the pump shaft. Leakage into the standpipe is constantly monitored.

Restriction Bushing

The restriction bushing provides a restriction between the fluid being pumped by the impeller, and the mechanical seal area, so that the flow is reduced or controlled.

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