Normal and Emergency Ventilation Systems


The typical nuclear plant has numerous ventilation systems that have traditional and/or emergency functions. Examples of such systems and their safety significance are noted. Hyperlinks lead to system flow diagrams.

BWR PWR Safety-Related
Primary Containment Ventilation Containment Fan Coil Units & Dome Fans x
Drywell Cooling Containment Cooling  
Reactor Building Ventilation Auxiliary Building  
Standby Gas Treatment Auxiliary Building Special Ventilation (Zone SV) x
  Shield Building Ventilation x
Control Room Air Conditioning Control Room Air Conditioning  
Emergency Filtration Control Room Post Accident Recirculation x
  Safeguards Ventilation x
Diesel Generator Ventilation Diesel Generator Ventilation x
Diesel Generator Building or Room Ventilation Diesel Generator Building or Room Ventilation  
Turbine Building Ventilation Turbine Building Ventilation  
Screenhouse Ventilation Screenhouse Ventilation x
Radwaste Building Ventilation    

Ventilation systems consist of ducts and dampers. Chillers, air conditioning units, or fan coil units may be used to cool the air passing through the ducts. Fans may be used to circulate the air. Filters may be used to remove impurities from the air. In general terms, the functions of these systems are:

Containment Emergency Cooling Systems

Filtration Systems

Pressure Differential Systems

Cooling Systems

Components and Flow Paths

Containment Emergency Cooling Systems

These systems usually have Fan Cooler Units which have a internal fan which can draw the hot moist air (that may be present during postulated accidents) across radiator type coils that are cooled by some external source, e.g. the Essential Service Water System. The cooled exhaust from these units is usually routed through a Duct to the top of containment where the air would be hotter. Separate Fans in the exhaust duct, sometimes called Dome Recirculation Fans, direct the flow to the containment dome.

Ventilation duct and Airlock in Containment


Control Rod Drive Cooling Ventilation above Reactor

Fan Coil Unit (closeup)>>>

Fans (e.g. Standby Gas Treatment)

Filtration Systems

These systems usually consist of Fans that draw the air from the potentially contaminated areas through PAC Filter Units. The PAC unit consists of 3 filter units -

After passing through the PAC unit, the exhaust may be routed to an exhaust stack.

Such systems will normally be actuated by radiation monitoring sensors mounted in the exhaust ducts. In addition, they will automatically start any time the emergency core cooling systems start or containment isolation is required.

In conjunction with these "special" or recirculation fans starting, the normal ventilation system equipment will shutdown with appropriate fans tripping and duct dampers closing or opening so that the filtration system is the only one operating.

Shield Building Vent Filter and Fan Control Room Filter Unit

Pressure Differential Systems 

Pressure differential systems depend on the flow rates of the various buildings' supply and exhaust fans. Such systems also take into account certain sizes of openings in the buildings. Because of this operators may be required to keep a log of all building openings and their size. The supply and exhaust fans are sized to create pressure differentials between the various buildings.

Turbine Building > Auxiliary or Reactor Building

Cooling Systems

Cooling systems usually consist of one of the following:

Copyright 1996-2005.  Joseph Gonyeau, P.E.. The Virtual Nuclear Tourist. All rights reserved. Revised: June 30, 2005.