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Each plenum has two systems, an automatic deluge system at the particle impingement
separation screens (demister screen) and a manually activated deluge system upstream of the
first stage of HEPA filters. The Building 991 roof plenum only has one stage of HEPA filters
while the Building 985 plenum has two stages of HEPAs.
The demister chambers for the Building 991 roof plenum and Building 985 are shown in
Figures 2-13 and 2-14. These chambers have nozzles located approximately six inches upstream
of the demister screen. The spray pattern is designed so that a water curtain is discharged to cool
the incoming air. The spray may also facilitate particulate removal. The capabilitv to observe
spray oatterns of the automatic portion of the deluge svstem in the Building 991 roof plenum is
significantly impaired due tu the close prorcimih7 of the filter stage to the plenum wall. That is,
the inlet plenum wall is verv close to the filter stage blocking view of some of the spray nozzles
due to limitations of .line of sight. Also. nozzle smass near observation ports degrade the
visibilitv of the spray for nozzles further awav from the observation port. The automatic plenum
deluge systems are defense-in-deDth systems and are nut credited controls in the safe@ analysis.
The adecluacv of this confirnation for a credited safetv system would be questionable since
nozzle sprav patterns for some portions ofthe plenum may not mitigate high air temperature or
hot ember and flvinp brand impacts on iilters (i.e.. certain areas of the filter stage may not be
cooled or protected against hot particulates). Heat detectors located in the inlet ducts to the filter
plenum actuate the automatic deluge valves. When high temperature air passes over the heat
detector, the contacts within the detector .change state at 190°F, which sends a signal to the
associated deluge control panel. The deluge control panel for the Building 991 roof plenum is
located in Room 130 and the panel for the Building 985 plenum deluge system is located in
Building 985. The deluge control panel simultaneously sends an alarm to the CAS and FDC (via
the Signal Input / Output (SIO) panel), sends an alarm to the deluge control panel, and sends a
signal to the solenoid that opens the automatic deluge valve. The deluge control panels have
batteries that provide backup power to the panel if alternating current (AC) power is lost. The
circuitry is supervised. A supervisory alarm is received at the FDC when AC or direct current
(DC) power is lost. The demister screens remove much of the water from the air stream before
it reaches the HEPA filters to protect the filtration capability of the filters.
The manually activated deluge system is located immediately upstream of the frrst stage
of HEPA filters. Deluge nozzles spray water directly onto the first stage of KEPA filters. The
manual deluge system provides an important emergency capability if the frrst stage of HEPA
filters is in danger of being consumed by fire. Activation of the system under such conditions,
however, will likely result in the loss of the first stage, either due to plugging by soaked
particulates (which will effectively stop ventilation), by partial plugging causing media failure,
or by direct damage. Failure of the first stage other than by plugging will subject remaining
downstream stages to the possibility of fire, heat, or physical damage.
The hazard and accident analysis credits the filtered exhaust ventilation svsterns in
Building 991 and 3uildina 985. The automztic pieiium deluge swteems are identified as
defense-in-depth systems for the filtered exhaust vendlation svsterns but are not credited in the
safetv analys&. The systems are to be maintained in their current configuration (i.e., not allowed
to dewade an17 fhrther than is currently realized) as added assurance for motection of the HEPA
Revision I Building 991 Complex FSAR
September 1999
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