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

WIPP RH PSAR DOE/WIPP-03-3174 CHAPTER 4
Under ordinary operating conditions, the pressure in W30 is higher (less negative) than that in the waste
shaft station (S400). On very hot days (exceeding 100E F [37.8E C]) the reduction of this differential
pressure caused by the negative NVP can result in the pressure in S400 being higher than in W30.
Without corrective actions, this would allow airflow from the CA area into a non-CA area.
4.4.3.3.3 Cold Weather NVP
During cold weather, the air going down to the underground is colder and denser (heavier) than the air
returning from the underground. This denser air has a natural tendency to sink down the AIS and SH
shaft (cold air sinks). In cold weather there is a positive NVP which augments the fan pressure. This
increases the airflow down the intake shafts, reduces the fan suction pressure (constant flow control) and
increases the differential pressure between the waste shaft station, waste disposal area, and the other
areas.
The WIPP mine ventilation system is designed for intake air to downcast in the AIS, SH shaft, and waste
shaft. The system pressure required to induce those down drafts is supplied by the surface fans. On
extreme cold weather days, a portion of the air entering the repository through the AIS and SH shaft may
be the result of a positive NVP. This air is entering the repository without the aid of the mechanical fans.
The fans in turn reduce their operating pressure because they are receiving a sufficient and constant
volume of air. Upcasting of the air in the waste shaft can occur if the situation is not corrected.
The air feeding the waste shaft comes primarily from the auxiliary air intake tunnel, partly from leakage
into the waste hoist tower, and partly from the WHB. The result is that the air feeding the waste shaft
tends to be warmer than the surface air feeding the AIS. The reduction in fan pressure, coupled with the
warmer air in the waste shaft is only under alternate, reduced, and minimum ventilation modes.
Administrative action is required to adjust the underground ventilation configuration to avoid reverse
flow in the waste shaft. There are several alternatives which can be performed concurrently to prevent or
correct this problem should it occur. They include:
Ä
Ä
Ä
Ä
Start second main exhaust fan (normal ventilation).
Open the regulator to the waste shaft station.
Cover the AIS and/or the SH shaft on the surface.
Close the regulators to the mining, waste disposal and experimental areas.
A pressure chamber has been constructed on the west side of the waste shaft station to ensure that leakage
from the CA side into the non-CA area does not occur. The pressure chamber is manually activated
whenever waste handling is occurring in the waste shaft and/or waste shaft station, and differential
pressure between S400 and W30 is low. The chamber is pressurized by six high pressure fans. The fans
are operated in various combinations to provide the airflow necessary to maintain the pressure buffer. As
a secondary backup system, pressure will be supplied by an actuated valve on a plant air pressurized line.
The valve will be controlled by a Foxboro controller to regulate the flow of air into the chamber and
maintain pressure differentials. The pressure inside the chamber is monitored to ensure that it is
sufficient to prevent airflow reversal even if the differential pressure from S400 to W30 (which is also
monitored) is in the wrong direction or positive NVP is sufficient to cause waste shaft reversal.
4.4-12 January 28, 2003