PWR Reactor Coolant Flow

Brian Chaffin
March 27, 2017

Submitted as coursework for PH241, Stanford University, Winter 2017

Coolant Flow in Pressurized Water Reactors

Fig. 1: The layout of Pressurized Water Reactor. (Source: Wikimedia Commons)

A critical component of the Pressurized Water Reactor (PWR), seen in Fig. 1, is the PWR Reactor Coolant System. The system has three major functions: Transferring the heat from the reactor for the steam generator, maintaining the pressure within acceptable limits, and maintaining the pressure boundary. This process is made possible by three main components of the machine: the steam generator, the pressurizer, and the reactant coolant pump. [1] Although, the three parts are somewhat different they are all greatly important to a well-functioning reactor.

In a vertical steam generator, reactor coolant from the hot leg comes in the bottom, and quickly passes through the inside of the tubes. The heat passes through the tubes to the "secondary side" where water supplied from the feed water system is heated up. This water is then converted to steam. In the upper part of the steam generator are moisture-separators which remove the water in the steam and divert it back into the lower part of the steam generator. [1] The "Pressurizer" in a Pressurized Water Reactor design maintains the pressure through heaters mounted in the bottom and a spray nozzle mounted in the upper part of the vessel. This pressure is normally maintained just above the critical pressure of water, so it enables the water work over the entire temperature range without boiling.

The Reactor Coolant Pump, which contains three major components the motor, the hydraulic section, and the seal package, is used to cool the machine. The motor is a large, air cooled, electric motor. [2] The horsepower rating of the motor must be high enough to provide the necessary flow of coolant for heat removal. The hydraulic section of the pump is the impeller and the discharge volute. The impeller of the pump is attached to the motor by a long shaft. The seal package is located between the motor and the hydraulic section and prevents any water from leaking up the shaft into the containment atmosphere. Any water that does leak up the shaft is collected and routed to the seal leak off system for collection in various systems. [2] As seen from the process above, the reactor operates as one big machine, but the other small machines inside of it are crucial for its functionality.

© Brian Chaffin. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] J. Ailloud and M. Monteil, "Pressurized Water Reactor," US Patent 4278500A, 2 Feb 79.

[2] Z. Yoran, "A Review of Natural Circulation Loops in Pressurized Water Reactors and Other Systems," Nucl. Eng. Des. 67, 203 (1981).