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

WIPP RH PSAR DOE/WIPP-03-3174 CHAPTER 4
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The design and construction shall follow conventional mining practices.
Structural analysis shall use data acquired from the WIPP underground.
Materials shall be compatible with their emplacement environment and function.
Treatment of surfaces in the closure areas shall be considered in the design.
Thermal cracking of concrete shall be addressed.
During construction, a QA/QC program shall be established to verify material properties and
construction practices.
Construction of the panel closure system shall consider shaft and underground access and services
for materials handling.
The final panel closure design 3 was prepared with the assumption that there would be no backfill in the
disposal rooms. With the inclusion of backfill, the design has been re-examined, and it has been
determined that the changes are insignificant for several reasons. First, the backfill has no effect on the
gas generation rate so that the values used in the design for gas generation and methane buildup remain
the same. Second, the quantity of backfill is sufficient to fill one-tenth of the void volume in the room.
This results in more rapid pressurization of the room; however, the effect is small and will only be
important after the facility is sealed. Third, the reduced volume will result in a faster concentration
buildup of methane. This would not result in a revision of the design. Instead, it would change the
criteria for installing explosion walls.
The design for the panel closure system calls for a composite panel barrier system consisting of a rigid
concrete plug with or without removal of the DRZ, and either an explosion-isolation wall or a
construction-isolation wall. The design basis for this closure is such that the migration of hazardous
waste constituents from closed panels during the operational and closure period would result in
concentrations at the WIPP facility well below health-based standards. The source term used as the
design basis included the average concentrations of VOCs from CH waste containers, as measured in
headspace gases through January 1995. The VOCs are assumed to have been released by diffusion
through the container vents, and are assumed to be in equilibrium with the air in the panel. Emissions
from the closed panel occur at a rate determined by gas generation within the waste and creep closure of
the panel. Due to the relatively small amount of RH waste (approximately five percent of the total waste
volume), VOC emissions from RH waste are assumed to contribute insignificantly to total VOC
emissions. This design meets the environmental performance standard.
Figures 4.2-34 and 4.2.35 show diagrams of the panel closure design and installation envelopes.
DOE/WIPP-96-2150 3 provides the detailed design, and the design analysis for the panel closure system.
The panel closure design is such that components can be added or removed, or their shapes adjusted
depending on the particular ground conditions at the time of installation. For example, in
DOE/WIPP-96-2150 3 , Option A represents the likely closure of panels less than 20 years old at the time
of final facility closure, and whose entries are sufficiently intact such that DRZ removal is not needed.
These would likely include Panels 6 through 8.
4.2-28 January 28, 2003