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dominant Fucili[v Fire Scenario I - I MW TRU Waste Ilrram Faciiitv Fire covers the necessarv
controls to define an acceptable facility configuration.
When the fiZfered exhaust ventiludon svstem is credited for fire scenario mitigation.
there is a possibilitv that the fire mav impact the HEPA filters due to hidl air temperatures or
hot embers and fipina brands. Either of these impacts can result in the ignition of the filter
stae. release of radioactive materials that were captured on the filter stage. and subsequent Ioss
of filtration cauabilitv. However. the six drum fire scenario is not expected to challenge the
filters due to elevated temperatures. It is also not expected that the sixdrum fire will have
sufficient veneration of hot embers and flving brands to challenge the filters due to hot
particulates. For l%es larger than the six drum Ere, the auformtic plenum d'uge systems can
provide Drotection for the HEPA filters against high temperatures and. to a lesser extent. against
hot embers and fl>7ing brands. The systems consist of an automatic delupe feature that sprays
into the plenum before the demister screen. a manually actuated deluge feature that bypasses the
automatic deluge portion of the ssstem and sprays before the demister screen. and a manualiv
acfuated deluge feature that spravs directly onto the frlter staye. This fatter feature directly wets
the fiiters and mav lead to stage failure due to water damage. Actuation of the direct filter spray
manual deluge system has the ~otential to save the filters from burnin- at the expense of failing
the filters due to wetting. Due to the IOW likelihood of the actuation or use of this svstem (large
fires challen@ng the filters are not considered to be credible) and the potential for filter stage
failure followinn use of the system. the aufomatic plenum deZuge sc;stems are not credited but
serve as a defense-in-depth mitigative feature for Drotection against verv large facilig fires.
In summary, creditinp the 3uiZdin.k 991 fiftered erkaust ventii&n Vsfem and fa&&
confimration controls would yield Risk Class IV results for the MOI and the CW.
Facilitv Fire Scenario 3 - Medium to Larpe Wooden LLW Crate Facilitv Fire
A facility fire is postulated to impact up to four wooden LLW crates. The facility fue is
postulated to occur as a result of combustibles being ignited during the conduct of hot work,
during the receipt or shipment of crates, or by exposure to electrical system components. The
facility fire occurs in the West Dock Canopy Area. The facility fire is assumed to initially
involve combustible materials located in close proximity to stored waste crates. The wooden
crates become involved in the frre and combust along with their contents that are assumed to be
combustible. The fire is limited to four wooden crates due to fire suppression by the automatic
sprinkler system once the fire is sufficiently large to actuate the system.
The postulated facility fire involving four wooden LLW crates in the West Dock Canopy
Area of the Building 991 Complex is considered to be an unlike& event with low consequences
for the MOI, moderate consequences for the CW, and low consequences for the IW. The CW
risk class is Risk Class II. The risk class for the MOI and the IW is Risk Class 111, which is
considered to be acceptable.
'
Acceptability of the risk class results for the CW is based on the conservatism of the
analysis @e., modeling input assumptions, defense-in-depth protective features not specifically
credited). If a median x/Q value and non-lofied plume is used in the analysis, the CW
Revision 1
4-32 Building 991 Complex FSAR
September I999 I