How to Size a Pump for the I2S LWR

Conclusion

Step 3 - Choose motor

Step 4 - Other considerations

• Flywheel
• Seals
• Cooling
• Damping

Step 1 - Desired conditions:

• Pump Head
• Flow Rate
• Estimated RPM range

Step 2 - Size Impeller

• Specific speed
• Power
• Water
• Brake
• Torque
• Impeller diameter

Step 4: Other Considerations

Seals

An important side consideration for choosing a pump is deciding how it should be sealed. One option is to bathe the entire pump in the fluid, including the motor, and only seal the electrical leads out of the casing. Another option is to place a seal between the rotor and the stator of the motor. This option is called a canned motor pump and it drops the overall efficiency of the pump. Another option is to use multiple mechanical seals between the impeller and the motor. This adds many bearings to the seals and also drops the efficiency of the pump.

Flywheel

A flywheel needs to be considered if pump coastdown is required. For a reactor coolant pump, in the case of loss of electricity, coastdown is required to prevent departure from nucleate boiling. The coastdown coefficient for our RCP is 5 seconds, which enables the reactor to safely shut off.

Damping

The damping comes mainly from the fluid in the system and the bearings that are needed for the rotating parts. The damping in a pump can be an important consideration because it affects many of the other factors in a pump. The efficiency of the pump can decrease depending on the damping. The sizing of the flywheel is dependent on the damping. This means that while sizing a pump deciding whether to use bushings or bearings, or whether to try rotating the motor in the fluid or seal it with the motor in air can affect other pieces in your system.

Cooling

Cooling for pumps can be handled in several different ways. Depending on the size of the motor it can either be air cooled, cooled by the fluid it is pumping, or it can have a separate cooling system.

The I2S reactor coolant pumps have a separate cooling system that pumps coolant through the motor and sends it to a heat exchanger.

What is the I2S Light Water Reactor?

Step 2: Sizing Impeller

I2S LWR stands for Integral, Inherently Safe Light Water Reactor.

It is a safe nuclear reactor with all of the irradiated water

contained within the pressure vessel. It outputs

1000 MW of electric power and has multiple

passively initiated backup systems. This means that

even without an operator present it can still shut down

and remain cool to prevent an accident.

To get the diameter of the impeller you need to calculate the specific speed and the required power.

Specific Speed

The specific speed is a non-dimensional number used in pump design to specify whether a centrifugal or axial pump should be used or what the efficiency of the pump will be. This graph shows which type of pump is best suited to which specific speed.

Power - Horsepower

Water horsepower is the minimum required power to move the water.

Impeller Size

Brake horsepower is the required power in the shaft due to impeller efficiency.

Since the specific speed is based on the angular velocity, we ended up with a large range of specific speeds which led us to decide that a centrifugal pump was best.

One of the most important parts of the pump is the impeller. The impeller forces the fluid to accelerate radially outwards increasing the pressure and the flow rate at the outer radius. That is why the impeller diameter is based on the pump head and flow rate that you need for your pump. The following equations show how diameter is based on the pump head and angular velocity.

This brake horse power is used to find the required shaft torque.

Step 3: Choose Motor

Where,

Results

Step 1: Starting Information

For the reactor coolant pump we found that the diameter of the impeller would be 21 inches due to the efficiency given from the specific speed on the previous graph.

MATLAB was used extensively to set up the equations given in the previous slides and compute the actual dimensions for the pump.

Other Dimensions needed to size an Impeller

The actual results for the I2S are:

An impeller diameter of 21 inches

Specific speed of 1.48

An angular velocity of 1400 rpm

A shaft horsepower of 1665 hp

An efficiency of about 87%

• Shaft Diameter
• Suction Line Velocity and Diameter
• Wheel Inlet Dimensions
• Number of Vanes
• Inlet and Outlet Vane Angle
• Impeller Width
• Outlet Velocity
• Leakage Loss
• Clearance Area

Specified conditions:

• Pump Head
• Flow Rate
• Estimated RPM range

Motor selection is the next phase in pump design. Online searches for information regarding the correct sizing of motors can be quite difficult. We recommend searching motor manufacturers websites for their online catalogs or calling them for more specific information. For sizing the casing of the motor check NEMA or other standard frame sizes such as WP-I.

I2S Motor Choice - Baldor WPI E7111

For the I2S LWR we were given a total pressure loss in the system and the flow rate required for cooling the fuel rods. For the RPM we started with normal range used in motors.

For the I2S LWR these Values are:

• Flow Rate: 2.0038 m^3/s
• Total Head: 74.3 m
• RPM Range: 0-2400 rpm

How to Size a Pump for the I2S LWR