Emergency Ventilation Systems


Function

The typical nuclear plant has a number of Emergency or Safeguards Ventilation Systems. The following are the types of systems used with their main functions.

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.

The figure below for the Kewaunee plant containment ventilation systems illustrates the flow paths and components used.

Courtesy US Nuclear Regulatory Commission

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.

The Maine Yankee plant diagram below illustrates this type of system.

Courtesy US Nuclear Regulatory Commission

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 1996-2004.  Joseph Gonyeau, P.E.. The Virtual Nuclear Tourist. All rights reserved. Revised: March 15, 2001.