DOE 2000. - Waste Isolation Pilot Plant - U.S. Department of Energy

WIPP RH PSAR DOE/WIPP-03-3174 CHAPTER 4
Major Components and Operating Characteristics - The ventilation system consists of six centrifugal
exhaust fans (three in the normal flow path and three in the filtration flow path), two identical HEPA
filter assemblies arranged in parallel, isolation and back draft dampers, filter bypass arrangement, and
associated duct work. Operation of the underground ventilation system is detailed in the WIPP procedure
WP 04-VU1608. 11
The six fans are divided into two groups. One group consists of three fans, which are used during normal
operation to provide an underground flow of 425,000 scfm (224 m 3 /s), and are located near the exhaust
shaft. One main fan can be operated to provide 260,000 scfm (123 m 3 /s). The remaining three fans,
rated at 60,000 scfm (28.3 m 3 /s) each, are located at the EFB and are capable of being used during the
filtered mode of operation. This mode of operation requires the use of only one of the three fans at any
given time with all other fans stopped and isolated. Two of the three filter mode fans can also be
operated (with the HEPA system bypassed) to provide other underground ventilation requirements, when
needed.
Each filter assembly consists of two banks of prefilters and two banks of HEPA filters arranged in series;
and, each assembly will handle 50 percent of the filtered mode airflow (30,000 cfm each [849.5 m 3 /m] ).
Any one of the three EFB fans is capable of delivering 100 percent of the design 60,000 scfm flow rate
with all filters at their maximum pressure drop. Fan failure is monitored by a flow sensing device on the
fan’s discharge side, and alarms in the CMR.
Safety Considerations and Controls - The operating status of the exhaust fans and the airborne
contamination level of the effluent discharged are displayed in the CMR. Provides a means to switch to
filtration.
An alarm for excessive pressure drop across the filters is actuated at a predetermined level. Filter
differential pressure is displayed locally and in the CMR.
Instruments and system components are accessible for periodic testing and inspection during normal
plant operation. Under normal operating conditions, the ventilation system functions continuously.
4.4.3.3.1 Natural Ventilation Pressure
The air flow in the underground is normally driven by the negative pressure induced by the exhaust fans.
There can be a second pressure resulting from the difference in density between the air entering and
leaving the repository which can influence airflow. This phenomenon is called the natural ventilation
pressure (NVP). It is experienced on days when outside temperatures are either very hot or very cold.
4.4.3.3.2 Hot Weather NVP
During hot weather, the air going down to the underground is warmer and less dense (lighter) than the air
returning from the underground. This lighter air has a natural tendency to resist being drawn down into
the repository (hot air rises). Hence in hot weather there is a (negative) NVP which opposes the fan
pressure. This reduces the flow down the AIS and SH shaft. It also reduces the differential pressures
between the waste shaft station, waste disposal area, and the other areas. The air in the waste shaft will
be cooler than that in the AIS and SH shaft, which further reduces the waste shaft station to W30
differential pressure. (See Figure 4.1-3 for U/G locations).
4.4-11 January 28, 2003