BWR Reactor Recirculation Systems

Function

The Recirculation System is used in the Boiling Water Reactor design. This system provides the following functions:

• Control of reactor power level through the variable speed recirculation pumps
• Cooling of the reactor during off-normal modes
• Paths for emergency makeup and chemical purification

Major Components

The Recirculation System consists of two (2) recirculation loops. Each loop consists of piping from the reactor to a recirculation pump, then piping to return the fluid back to the reactor. The recirculation pumps are driven by variable speed motors. As the speed increases, more voids are swept from the core, resulting in more thermal neutrons being produced. This, in turn, results in increasing power.

Jet pumps are considered as part of the reactor cooling system. The pumps are installed in the annular region between the core barrel and the outside reactor vessel. The driving head for these jet pumps is provided by the pressure head provided by the discharge of the recirculation pumps.

Penetrations

Several penetrations come off the recirculation loop, including:

• the reactor water cleanup system used to purify the reactor coolant,
• the shutdown cooling system, used to cool the reactor below 350F

Penetrations providing water to the recirculation system include:

• low pressure coolant injection to provide emergency makeup to cool the reactor at low pressure and high flowrate (~2000-3000 gpm),
• shutdown cooling system to return cooled water back to the reactor,
• isolation condenser, if used, to return cooled water back to the reactor. The isolation condenser is used to cool steam from the reactor if the main steam isolation valves close. The water is returned to the reactor by natural circulation. Pumped flow is not required.

Motor valves

Motor operated valves are typically provided for isolating the recirculation pumps for maintenance.

Instruments

The key instrument typically provided for this system is the flow rate.

Flow diagrams

The NRC provides a very informative manual showing the various BWR systems, including the recirc system.

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